[v4,1/7] interconnect: Add generic on-chip interconnect API

Commit Message

Georgi Djakov March 9, 2018, 9:09 p.m. UTC

This patch introduce a new API to get requirements and configure the
interconnect buses across the entire chipset to fit with the current
demand.

The API is using a consumer/provider-based model, where the providers are
the interconnect buses and the consumers could be various drivers.
The consumers request interconnect resources (path) between endpoints and
set the desired constraints on this data flow path. The providers receive
requests from consumers and aggregate these requests for all master-slave
pairs on that path. Then the providers configure each participating in the
topology node according to the requested data flow path, physical links and
constraints. The topology could be complicated and multi-tiered and is SoC
specific.

Signed-off-by: Georgi Djakov <[e-mail]>
---
 Documentation/interconnect/interconnect.rst |  96 ++++++
 drivers/Kconfig                             |   2 +
 drivers/Makefile                            |   1 +
 drivers/interconnect/Kconfig                |  10 +
 drivers/interconnect/Makefile               |   1 +
 drivers/interconnect/core.c                 | 489 ++++++++++++++++++++++++++++
 include/linux/interconnect-provider.h       | 109 +++++++
 include/linux/interconnect.h                |  40 +++
 8 files changed, 748 insertions(+)
 create mode 100644 Documentation/interconnect/interconnect.rst
 create mode 100644 drivers/interconnect/Kconfig
 create mode 100644 drivers/interconnect/Makefile
 create mode 100644 drivers/interconnect/core.c
 create mode 100644 include/linux/interconnect-provider.h
 create mode 100644 include/linux/interconnect.h

Comments

Matthias Kaehlcke April 6, 2018, 5:38 p.m. UTC | #1

On Fri, Mar 09, 2018 at 11:09:52PM +0200, Georgi Djakov wrote:
> This patch introduce a new API to get requirements and configure the
> interconnect buses across the entire chipset to fit with the current
> demand.
> 
> The API is using a consumer/provider-based model, where the providers are
> the interconnect buses and the consumers could be various drivers.
> The consumers request interconnect resources (path) between endpoints and
> set the desired constraints on this data flow path. The providers receive
> requests from consumers and aggregate these requests for all master-slave
> pairs on that path. Then the providers configure each participating in the
> topology node according to the requested data flow path, physical links and
> constraints. The topology could be complicated and multi-tiered and is SoC
> specific.
> 
> Signed-off-by: Georgi Djakov <[e-mail]>
> ---
>  Documentation/interconnect/interconnect.rst |  96 ++++++
>  drivers/Kconfig                             |   2 +
>  drivers/Makefile                            |   1 +
>  drivers/interconnect/Kconfig                |  10 +
>  drivers/interconnect/Makefile               |   1 +
>  drivers/interconnect/core.c                 | 489 ++++++++++++++++++++++++++++
>  include/linux/interconnect-provider.h       | 109 +++++++
>  include/linux/interconnect.h                |  40 +++
>  8 files changed, 748 insertions(+)
>  create mode 100644 Documentation/interconnect/interconnect.rst
>  create mode 100644 drivers/interconnect/Kconfig
>  create mode 100644 drivers/interconnect/Makefile
>  create mode 100644 drivers/interconnect/core.c
>  create mode 100644 include/linux/interconnect-provider.h
>  create mode 100644 include/linux/interconnect.h
> 
> diff --git a/Documentation/interconnect/interconnect.rst b/Documentation/interconnect/interconnect.rst
> new file mode 100644
> index 000000000000..23eba68e8424
> --- /dev/null
> +++ b/Documentation/interconnect/interconnect.rst
> @@ -0,0 +1,96 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=====================================
> +GENERIC SYSTEM INTERCONNECT SUBSYSTEM
> +=====================================
> +
> +Introduction
> +------------
> +
> +This framework is designed to provide a standard kernel interface to control
> +the settings of the interconnects on a SoC. These settings can be throughput,
> +latency and priority between multiple interconnected devices or functional
> +blocks. This can be controlled dynamically in order to save power or provide
> +maximum performance.
> +
> +The interconnect bus is a hardware with configurable parameters, which can be
> +set on a data path according to the requests received from various drivers.
> +An example of interconnect buses are the interconnects between various
> +components or functional blocks in chipsets. There can be multiple interconnects
> +on a SoC that can be multi-tiered.
> +
> +Below is a simplified diagram of a real-world SoC interconnect bus topology.
> +
> +::
> +
> + +----------------+    +----------------+
> + | HW Accelerator |--->|      M NoC     |<---------------+
> + +----------------+    +----------------+                |
> +                         |      |                    +------------+
> +  +-----+  +-------------+      V       +------+     |            |
> +  | DDR |  |                +--------+  | PCIe |     |            |
> +  +-----+  |                | Slaves |  +------+     |            |
> +    ^ ^    |                +--------+     |         |   C NoC    |
> +    | |    V                               V         |            |
> + +------------------+   +------------------------+   |            |   +-----+
> + |                  |-->|                        |-->|            |-->| CPU |
> + |                  |-->|                        |<--|            |   +-----+
> + |     Mem NoC      |   |         S NoC          |   +------------+
> + |                  |<--|                        |---------+    |
> + |                  |<--|                        |<------+ |    |   +--------+
> + +------------------+   +------------------------+       | |    +-->| Slaves |
> +   ^  ^    ^    ^          ^                             | |        +--------+
> +   |  |    |    |          |                             | V
> + +------+  |  +-----+   +-----+  +---------+   +----------------+   +--------+
> + | CPUs |  |  | GPU |   | DSP |  | Masters |-->|       P NoC    |-->| Slaves |
> + +------+  |  +-----+   +-----+  +---------+   +----------------+   +--------+
> +           |
> +       +-------+
> +       | Modem |
> +       +-------+
> +
> +Terminology
> +-----------
> +
> +Interconnect provider is the software definition of the interconnect hardware.
> +The interconnect providers on the above diagram are M NoC, S NoC, C NoC and Mem
> +NoC.

Should P NoC be part of that list?

> +
> +Interconnect node is the software definition of the interconnect hardware
> +port. Each interconnect provider consists of multiple interconnect nodes,
> +which are connected to other SoC components including other interconnect
> +providers. The point on the diagram where the CPUs connects to the memory is
> +called an interconnect node, which belongs to the Mem NoC interconnect provider.
> +
> +Interconnect endpoints are the first or the last element of the path. Every
> +endpoint is a node, but not every node is an endpoint.
> +
> +Interconnect path is everything between two endpoints including all the nodes
> +that have to be traversed to reach from a source to destination node. It may
> +include multiple master-slave pairs across several interconnect providers.
> +
> +Interconnect consumers are the entities which make use of the data paths exposed
> +by the providers. The consumers send requests to providers requesting various
> +throughput, latency and priority. Usually the consumers are device drivers, that
> +send request based on their needs. An example for a consumer is a video decoder
> +that supports various formats and image sizes.
> +
> +Interconnect providers
> +----------------------
> +
> +Interconnect provider is an entity that implements methods to initialize and
> +configure a interconnect bus hardware. The interconnect provider drivers should
> +be registered with the interconnect provider core.
> +
> +The interconnect framework provider API functions are documented in
> +.. kernel-doc:: include/linux/interconnect-provider.h
> +
> +Interconnect consumers
> +----------------------
> +
> +Interconnect consumers are the clients which use the interconnect APIs to
> +get paths between endpoints and set their bandwidth/latency/QoS requirements
> +for these interconnect paths.
> +
> +The interconnect framework consumer API functions are documented in
> +.. kernel-doc:: include/linux/interconnect.h
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index 879dc0604cba..96a1db022cee 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -219,4 +219,6 @@ source "drivers/siox/Kconfig"
>  
>  source "drivers/slimbus/Kconfig"
>  
> +source "drivers/interconnect/Kconfig"
> +
>  endmenu
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 24cd47014657..0cca95740d9b 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -185,3 +185,4 @@ obj-$(CONFIG_TEE)		+= tee/
>  obj-$(CONFIG_MULTIPLEXER)	+= mux/
>  obj-$(CONFIG_UNISYS_VISORBUS)	+= visorbus/
>  obj-$(CONFIG_SIOX)		+= siox/
> +obj-$(CONFIG_INTERCONNECT)	+= interconnect/
> diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig
> new file mode 100644
> index 000000000000..a261c7d41deb
> --- /dev/null
> +++ b/drivers/interconnect/Kconfig
> @@ -0,0 +1,10 @@
> +menuconfig INTERCONNECT
> +	tristate "On-Chip Interconnect management support"
> +	help
> +	  Support for management of the on-chip interconnects.
> +
> +	  This framework is designed to provide a generic interface for
> +	  managing the interconnects in a SoC.
> +
> +	  If unsure, say no.
> +
> diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
> new file mode 100644
> index 000000000000..5edf0ae80818
> --- /dev/null
> +++ b/drivers/interconnect/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_INTERCONNECT)		+= core.o
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> new file mode 100644
> index 000000000000..6306e258b9b9
> --- /dev/null
> +++ b/drivers/interconnect/core.c
> @@ -0,0 +1,489 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Interconnect framework core driver
> + *
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/idr.h>
> +#include <linux/init.h>
> +#include <linux/interconnect.h>
> +#include <linux/interconnect-provider.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +static DEFINE_IDR(icc_idr);
> +static LIST_HEAD(icc_provider_list);
> +static DEFINE_MUTEX(icc_provider_list_mutex);
> +static DEFINE_MUTEX(icc_path_mutex);
> +
> +/**
> + * struct icc_req - constraints that are attached to each node
> + *
> + * @req_node: entry in list of requests for the particular @node
> + * @node: the interconnect node to which this constraint applies
> + * @avg_bw: an integer describing the average bandwidth in kbps
> + * @peak_bw: an integer describing the peak bandwidth in kbps
> + */
> +struct icc_req {
> +	struct hlist_node req_node;
> +	struct icc_node *node;
> +	u32 avg_bw;
> +	u32 peak_bw;
> +};
> +
> +/**
> + * struct icc_path - interconnect path structure
> + * @num_nodes: number of hops (nodes)
> + * @reqs: array of the requests applicable to this path of nodes
> + */
> +struct icc_path {
> +	size_t num_nodes;
> +	struct icc_req reqs[0];
> +};
> +
> +static struct icc_node *node_find(const int id)
> +{
> +	struct icc_node *node;
> +
> +	node = idr_find(&icc_idr, id);
> +
> +	return node;
> +}
> +
> +static struct icc_path *path_allocate(struct icc_node *node, ssize_t num_nodes)
> +{
> +	struct icc_path *path;
> +	size_t i;
> +
> +	path = kzalloc(sizeof(*path) + num_nodes * sizeof(*path->reqs),
> +		       GFP_KERNEL);
> +	if (!path)
> +		return ERR_PTR(-ENOMEM);
> +
> +	path->num_nodes = num_nodes;
> +
> +	for (i = 0; i < num_nodes; i++) {
> +		hlist_add_head(&path->reqs[i].req_node, &node->req_list);
> +
> +		path->reqs[i].node = node;
> +		/* reference to previous node was saved during path traversal */
> +		node = node->reverse;
> +	}
> +
> +	return path;
> +}
> +
> +static struct icc_path *path_find(struct icc_node *src, struct icc_node *dst)
> +{
> +	struct icc_node *node = NULL;
> +	struct list_head traverse_list;
> +	struct list_head edge_list;
> +	struct list_head tmp_list;
> +	size_t i, number = 0;
> +	bool found = false;
> +
> +	INIT_LIST_HEAD(&traverse_list);
> +	INIT_LIST_HEAD(&edge_list);
> +	INIT_LIST_HEAD(&tmp_list);
> +
> +	list_add_tail(&src->search_list, &traverse_list);
> +
> +	do {
> +		list_for_each_entry(node, &traverse_list, search_list) {
> +			if (node == dst) {
> +				found = true;
> +				list_add(&node->search_list, &tmp_list);
> +				break;
> +			}
> +			for (i = 0; i < node->num_links; i++) {
> +				struct icc_node *tmp = node->links[i];
> +
> +				if (!tmp)
> +					return ERR_PTR(-ENOENT);
> +
> +				if (tmp->is_traversed)
> +					continue;
> +
> +				tmp->is_traversed = true;
> +				tmp->reverse = node;
> +				list_add_tail(&tmp->search_list, &edge_list);
> +			}
> +		}
> +		if (found)
> +			break;
> +
> +		list_splice_init(&traverse_list, &tmp_list);
> +		list_splice_init(&edge_list, &traverse_list);
> +
> +		/* count the number of nodes */
> +		number++;
> +
> +	} while (!list_empty(&traverse_list));
> +
> +	/* reset the traversed state */
> +	list_for_each_entry(node, &tmp_list, search_list)
> +		node->is_traversed = false;
> +
> +	if (found)
> +		return path_allocate(dst, number);
> +
> +	return ERR_PTR(-EPROBE_DEFER);
> +}
> +
> +static int path_init(struct icc_path *path)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +
> +		mutex_lock(&node->provider->lock);
> +		node->provider->users++;
> +		mutex_unlock(&node->provider->lock);
> +	}
> +
> +	return 0;
> +}
> +
> +static void node_aggregate(struct icc_node *node)
> +{
> +	struct icc_req *r;
> +	u32 agg_avg = 0;

Should this be u64 to avoid overflow in case of a large number of
constraints and high bandwidths?

> +	u32 agg_peak = 0;
> +
> +	hlist_for_each_entry(r, &node->req_list, req_node) {
> +		/* sum(averages) and max(peaks) */
> +		agg_avg += r->avg_bw;
> +		agg_peak = max(agg_peak, r->peak_bw);
> +	}
> +
> +	node->avg_bw = agg_avg;

Is it really intended to store the sum of averages here rather than
the overall average?

> +	node->peak_bw = agg_peak;
> +}
> +
> +static void provider_aggregate(struct icc_provider *provider, u32 *avg_bw,
> +			       u32 *peak_bw)
> +{
> +	struct icc_node *n;
> +	u32 agg_avg = 0;

See above.

> +	u32 agg_peak = 0;
> +
> +	/* aggregate for the interconnect provider */
> +	list_for_each_entry(n, &provider->nodes, node_list) {
> +		/* sum the average and max the peak */
> +		agg_avg += n->avg_bw;
> +		agg_peak = max(agg_peak, n->peak_bw);
> +	}
> +
> +	*avg_bw = agg_avg;

See above.

> +	*peak_bw = agg_peak;
> +}
> +
> +static int constraints_apply(struct icc_path *path)
> +{
> +	struct icc_node *next, *prev = NULL;
> +	int i;
> +
> +	for (i = 0; i < path->num_nodes; i++, prev = next) {
> +		struct icc_provider *provider;
> +		u32 avg_bw = 0;
> +		u32 peak_bw = 0;
> +		int ret;
> +
> +		next = path->reqs[i].node;
> +		/*
> +		 * Both endpoints should be valid master-slave pairs of the
> +		 * same interconnect provider that will be configured.
> +		 */
> +		if (!next || !prev)
> +			continue;
> +
> +		if (next->provider != prev->provider)
> +			continue;
> +
> +		provider = next->provider;
> +		mutex_lock(&provider->lock);
> +
> +		/* aggregate requests for the provider */
> +		provider_aggregate(provider, &avg_bw, &peak_bw);
> +
> +		if (provider->set) {
> +			/* set the constraints */
> +			ret = provider->set(prev, next, avg_bw, peak_bw);
> +		}
> +
> +		mutex_unlock(&provider->lock);
> +
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * icc_set() - set constraints on an interconnect path between two endpoints
> + * @path: reference to the path returned by icc_get()
> + * @avg_bw: average bandwidth in kbps
> + * @peak_bw: peak bandwidth in kbps
> + *
> + * This function is used by an interconnect consumer to express its own needs
> + * in term of bandwidth and QoS for a previously requested path between two
> + * endpoints. The requests are aggregated and each node is updated accordingly.
> + *
> + * Returns 0 on success, or an approproate error code otherwise.
> + */
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +	int ret;
> +
> +	if (!path)
> +		return 0;
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +
> +		mutex_lock(&icc_path_mutex);
> +
> +		/* update the consumer request for this path */
> +		path->reqs[i].avg_bw = avg_bw;
> +		path->reqs[i].peak_bw = peak_bw;
> +
> +		/* aggregate requests for this node */
> +		node_aggregate(node);
> +
> +		mutex_unlock(&icc_path_mutex);
> +	}
> +
> +	ret = constraints_apply(path);
> +	if (ret)
> +		pr_err("interconnect: error applying constraints (%d)", ret);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(icc_set);
> +
> +/**
> + * icc_get() - return a handle for path between two endpoints
> + * @src_id: source device port id
> + * @dst_id: destination device port id
> + *
> + * This function will search for a path between two endpoints and return an
> + * icc_path handle on success. Use icc_put() to release
> + * constraints when the they are not needed anymore.
> + *
> + * Return: icc_path pointer on success, or ERR_PTR() on error
> + */
> +struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +	struct icc_node *src, *dst;
> +	struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
> +
> +	src = node_find(src_id);
> +	if (!src)
> +		goto out;
> +
> +	dst = node_find(dst_id);
> +	if (!dst)
> +		goto out;
> +
> +	mutex_lock(&icc_path_mutex);
> +	path = path_find(src, dst);
> +	mutex_unlock(&icc_path_mutex);
> +	if (IS_ERR(path))
> +		goto out;
> +
> +	path_init(path);
> +
> +out:
> +	return path;
> +}
> +EXPORT_SYMBOL_GPL(icc_get);
> +
> +/**
> + * icc_put() - release the reference to the icc_path
> + * @path: interconnect path
> + *
> + * Use this function to release the constraints on a path when the path is
> + * no longer needed. The constraints will be re-aggregated.
> + */
> +void icc_put(struct icc_path *path)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +	int ret;
> +
> +	if (!path || WARN_ON_ONCE(IS_ERR(path)))
> +		return;
> +
> +	ret = icc_set(path, 0, 0);
> +	if (ret)
> +		pr_err("%s: error (%d)\n", __func__, ret);
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +		hlist_del(&path->reqs[i].req_node);
> +
> +		mutex_lock(&node->provider->lock);
> +		node->provider->users--;
> +		mutex_unlock(&node->provider->lock);
> +	}
> +
> +	kfree(path);
> +}
> +EXPORT_SYMBOL_GPL(icc_put);
> +
> +/**
> + * icc_node_create() - create a node
> + * @id: node id
> + *
> + * Return: icc_node pointer on success, or ERR_PTR() on error
> + */
> +struct icc_node *icc_node_create(int id)
> +{
> +	struct icc_node *node;
> +
> +	/* check if node already exists */
> +	node = node_find(id);
> +	if (node)
> +		return node;
> +
> +	node = kzalloc(sizeof(*node), GFP_KERNEL);
> +	if (!node)
> +		return ERR_PTR(-ENOMEM);
> +
> +	id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
> +	if (WARN(id < 0, "couldn't get idr"))
> +		return ERR_PTR(id);
> +
> +	node->id = id;
> +
> +	return node;
> +}
> +EXPORT_SYMBOL_GPL(icc_node_create);
> +
> +/**
> + * icc_link_create() - create a link between two nodes
> + * @src_id: source node id
> + * @dst_id: destination node id
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +	struct icc_node *dst;
> +	struct icc_node **new;
> +	int ret = 0;
> +
> +	if (IS_ERR_OR_NULL(node))
> +		return PTR_ERR(node);
> +
> +	mutex_lock(&node->provider->lock);
> +
> +	dst = node_find(dst_id);
> +	if (!dst)
> +		dst = icc_node_create(dst_id);
> +
> +	new = krealloc(node->links,
> +		       (node->num_links + 1) * sizeof(*node->links),
> +		       GFP_KERNEL);
> +	if (!new) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	node->links = new;
> +	node->links[node->num_links++] = dst;
> +
> +out:
> +	mutex_unlock(&node->provider->lock);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_link_create);
> +
> +/**
> + * icc_add_node() - add an interconnect node to interconnect provider
> + * @node: pointer to the interconnect node
> + * @provider: pointer to the interconnect provider
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +	if (WARN_ON(!node))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!provider))
> +		return -EINVAL;
> +
> +	node->provider = provider;
> +
> +	mutex_lock(&provider->lock);
> +	list_add_tail(&node->node_list, &provider->nodes);
> +	mutex_unlock(&provider->lock);
> +
> +	return 0;
> +}
> +
> +/**
> + * icc_add_provider() - add a new interconnect provider
> + * @icc_provider: the interconnect provider that will be added into topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_add_provider(struct icc_provider *provider)
> +{
> +	if (WARN_ON(!provider))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!provider->set))
> +		return -EINVAL;
> +
> +	mutex_init(&provider->lock);
> +	INIT_LIST_HEAD(&provider->nodes);
> +
> +	mutex_lock(&icc_provider_list_mutex);
> +	list_add(&provider->provider_list, &icc_provider_list);
> +	mutex_unlock(&icc_provider_list_mutex);
> +
> +	dev_dbg(provider->dev, "interconnect provider added to topology\n");
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_add_provider);
> +
> +/**
> + * icc_del_provider() - delete previously added interconnect provider
> + * @icc_provider: the interconnect provider that will be removed from topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_del_provider(struct icc_provider *provider)
> +{
> +	mutex_lock(&provider->lock);
> +	if (provider->users) {
> +		pr_warn("interconnect provider still has %d users\n",
> +			provider->users);
> +	}
> +	mutex_unlock(&provider->lock);
> +
> +	mutex_lock(&icc_provider_list_mutex);
> +	list_del(&provider->provider_list);
> +	mutex_unlock(&icc_provider_list_mutex);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_del_provider);
> +
> +MODULE_AUTHOR("Georgi Djakov <[e-mail]");
> +MODULE_DESCRIPTION("Interconnect Driver Core");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/interconnect-provider.h b/include/linux/interconnect-provider.h
> new file mode 100644
> index 000000000000..779b5b5b1306
> --- /dev/null
> +++ b/include/linux/interconnect-provider.h
> @@ -0,0 +1,109 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_PROVIDER_H
> +#define _LINUX_INTERCONNECT_PROVIDER_H
> +
> +#include <linux/interconnect.h>
> +
> +struct icc_node;
> +
> +/**
> + * struct icc_provider - interconnect provider (controller) entity that might
> + * provide multiple interconnect controls
> + *
> + * @provider_list: list of the registered interconnect providers
> + * @nodes: internal list of the interconnect provider nodes
> + * @set: pointer to device specific set operation function
> + * @dev: the device this interconnect provider belongs to
> + * @lock: lock to provide consistency during aggregation/update of constraints
> + * @users: count of active users
> + * @data: pointer to private data
> + */
> +struct icc_provider {
> +	struct list_head	provider_list;
> +	struct list_head	nodes;
> +	int (*set)(struct icc_node *src, struct icc_node *dst,
> +		   u32 avg_bw, u32 peak_bw);
> +	struct device		*dev;
> +	struct mutex		lock;
> +	int			users;
> +	void			*data;
> +};
> +
> +/**
> + * struct icc_node - entity that is part of the interconnect topology
> + *
> + * @id: platform specific node id
> + * @name: node name used in debugfs
> + * @links: a list of targets where we can go next when traversing
> + * @num_links: number of links to other interconnect nodes
> + * @provider: points to the interconnect provider of this node
> + * @node_list: list of interconnect nodes associated with @provider
> + * @search_list: list used when walking the nodes graph
> + * @reverse: pointer to previous node when walking the nodes graph
> + * @is_traversed: flag that is used when walking the nodes graph
> + * @req_list: a list of QoS constraint requests associated with this node
> + * @avg_bw: aggregated value of average bandwidth
> + * @peak_bw: aggregated value of peak bandwidth
> + * @data: pointer to private data
> + */
> +struct icc_node {
> +	int			id;
> +	const char              *name;
> +	struct icc_node		**links;
> +	size_t			num_links;
> +
> +	struct icc_provider	*provider;
> +	struct list_head	node_list;
> +	struct list_head	orphan_list;

orphan_list is not used (nor documented)

> +	struct list_head	search_list;
> +	struct icc_node		*reverse;
> +	bool			is_traversed;
> +	struct hlist_head	req_list;
> +	u32			avg_bw;
> +	u32			peak_bw;
> +	void			*data;
> +};
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_node *icc_node_create(int id);
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider);
> +int icc_link_create(struct icc_node *node, const int dst_id);
> +int icc_add_provider(struct icc_provider *provider);
> +int icc_del_provider(struct icc_provider *provider);
> +
> +#else
> +
> +static inline struct icc_node *icc_node_create(int id)
> +{
> +	return ERR_PTR(-ENOTSUPP);
> +}
> +
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_add_provider(struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_del_provider(struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* _LINUX_INTERCONNECT_PROVIDER_H */
> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
> new file mode 100644
> index 000000000000..5a7cf72b76a5
> --- /dev/null
> +++ b/include/linux/interconnect.h
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_H
> +#define _LINUX_INTERCONNECT_H
> +
> +#include <linux/types.h>
> +#include <linux/mutex.h>
> +
> +struct icc_path;
> +struct device;
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_path *icc_get(const int src_id, const int dst_id);
> +void icc_put(struct icc_path *path);
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw);
> +
> +#else
> +
> +static inline struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +	return NULL;
> +}
> +
> +static inline void icc_put(struct icc_path *path)
> +{
> +}
> +
> +static inline int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +	return 0;
> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* _LINUX_INTERCONNECT_H */

Georgi Djakov April 12, 2018, 1:06 p.m. UTC | #2

Hi Matthias,

On 04/06/2018 08:38 PM, Matthias Kaehlcke wrote:
> On Fri, Mar 09, 2018 at 11:09:52PM +0200, Georgi Djakov wrote:
>> This patch introduce a new API to get requirements and configure the
>> interconnect buses across the entire chipset to fit with the current
>> demand.
>>
>> The API is using a consumer/provider-based model, where the providers are
>> the interconnect buses and the consumers could be various drivers.
>> The consumers request interconnect resources (path) between endpoints and
>> set the desired constraints on this data flow path. The providers receive
>> requests from consumers and aggregate these requests for all master-slave
>> pairs on that path. Then the providers configure each participating in the
>> topology node according to the requested data flow path, physical links and
>> constraints. The topology could be complicated and multi-tiered and is SoC
>> specific.
>>
>> Signed-off-by: Georgi Djakov <[e-mail]>
>> ---
>>  Documentation/interconnect/interconnect.rst |  96 ++++++
>>  drivers/Kconfig                             |   2 +
>>  drivers/Makefile                            |   1 +
>>  drivers/interconnect/Kconfig                |  10 +
>>  drivers/interconnect/Makefile               |   1 +
>>  drivers/interconnect/core.c                 | 489 ++++++++++++++++++++++++++++
>>  include/linux/interconnect-provider.h       | 109 +++++++
>>  include/linux/interconnect.h                |  40 +++
>>  8 files changed, 748 insertions(+)
>>  create mode 100644 Documentation/interconnect/interconnect.rst
>>  create mode 100644 drivers/interconnect/Kconfig
>>  create mode 100644 drivers/interconnect/Makefile
>>  create mode 100644 drivers/interconnect/core.c
>>  create mode 100644 include/linux/interconnect-provider.h
>>  create mode 100644 include/linux/interconnect.h
>>
>> diff --git a/Documentation/interconnect/interconnect.rst b/Documentation/interconnect/interconnect.rst
>> new file mode 100644
>> index 000000000000..23eba68e8424
>> --- /dev/null
>> +++ b/Documentation/interconnect/interconnect.rst

[..]

>> +Terminology
>> +-----------
>> +
>> +Interconnect provider is the software definition of the interconnect hardware.
>> +The interconnect providers on the above diagram are M NoC, S NoC, C NoC and Mem
>> +NoC.
> 
> Should P NoC be part of that list?
> 

Yes, it should be!

>> +
>> +Interconnect node is the software definition of the interconnect hardware
>> +port. Each interconnect provider consists of multiple interconnect nodes,
>> +which are connected to other SoC components including other interconnect
>> +providers. The point on the diagram where the CPUs connects to the memory is
>> +called an interconnect node, which belongs to the Mem NoC interconnect provider.
>> +
>> +Interconnect endpoints are the first or the last element of the path. Every
>> +endpoint is a node, but not every node is an endpoint.
>> +
>> +Interconnect path is everything between two endpoints including all the nodes
>> +that have to be traversed to reach from a source to destination node. It may
>> +include multiple master-slave pairs across several interconnect providers.
>> +
>> +Interconnect consumers are the entities which make use of the data paths exposed
>> +by the providers. The consumers send requests to providers requesting various
>> +throughput, latency and priority. Usually the consumers are device drivers, that
>> +send request based on their needs. An example for a consumer is a video decoder
>> +that supports various formats and image sizes.
>> +
>> +Interconnect providers
>> +----------------------

[..]

>> +static void node_aggregate(struct icc_node *node)
>> +{
>> +	struct icc_req *r;
>> +	u32 agg_avg = 0;
> 
> Should this be u64 to avoid overflow in case of a large number of
> constraints and high bandwidths?

These values are proposed to be in kbps and u32 seems to be enough for
now, but in the future we can switch to u64 if needed.

> 
>> +	u32 agg_peak = 0;
>> +
>> +	hlist_for_each_entry(r, &node->req_list, req_node) {
>> +		/* sum(averages) and max(peaks) */
>> +		agg_avg += r->avg_bw;
>> +		agg_peak = max(agg_peak, r->peak_bw);
>> +	}
>> +
>> +	node->avg_bw = agg_avg;
> 
> Is it really intended to store the sum of averages here rather than
> the overall average?

Yes, the intention is to sum all the averages in total, so that the
hardware is set in a state that would be able to handle the total
bandwidth passing through a node.

Also in the next version of this patch i have changed this part a bit,
so that the aggregation could be customized and made platform specific,
as different platforms could use their own aggregation algorithms other
than the default sum/max.

> 
>> +	node->peak_bw = agg_peak;
>> +}
>> +
>> +static void provider_aggregate(struct icc_provider *provider, u32 *avg_bw,
>> +			       u32 *peak_bw)
>> +{
>> +	struct icc_node *n;
>> +	u32 agg_avg = 0;
> 
> See above.
> 
>> +	u32 agg_peak = 0;
>> +
>> +	/* aggregate for the interconnect provider */
>> +	list_for_each_entry(n, &provider->nodes, node_list) {
>> +		/* sum the average and max the peak */
>> +		agg_avg += n->avg_bw;
>> +		agg_peak = max(agg_peak, n->peak_bw);
>> +	}
>> +
>> +	*avg_bw = agg_avg;
> 
> See above.
> 
>> +	*peak_bw = agg_peak;
>> +}
>> +

[..]

>> +/**
>> + * struct icc_node - entity that is part of the interconnect topology
>> + *
>> + * @id: platform specific node id
>> + * @name: node name used in debugfs
>> + * @links: a list of targets where we can go next when traversing
>> + * @num_links: number of links to other interconnect nodes
>> + * @provider: points to the interconnect provider of this node
>> + * @node_list: list of interconnect nodes associated with @provider
>> + * @search_list: list used when walking the nodes graph
>> + * @reverse: pointer to previous node when walking the nodes graph
>> + * @is_traversed: flag that is used when walking the nodes graph
>> + * @req_list: a list of QoS constraint requests associated with this node
>> + * @avg_bw: aggregated value of average bandwidth
>> + * @peak_bw: aggregated value of peak bandwidth
>> + * @data: pointer to private data
>> + */
>> +struct icc_node {
>> +	int			id;
>> +	const char              *name;
>> +	struct icc_node		**links;
>> +	size_t			num_links;
>> +
>> +	struct icc_provider	*provider;
>> +	struct list_head	node_list;
>> +	struct list_head	orphan_list;
> 
> orphan_list is not used (nor documented)

It's not used anymore. Will remove!

Thanks,
Georgi

Evan Green May 11, 2018, 9:30 p.m. UTC | #3

Hi Georgi,

On Fri, Mar 9, 2018 at 1:12 PM Georgi Djakov <[e-mail]>
wrote:

> This patch introduce a new API to get requirements and configure the
> interconnect buses across the entire chipset to fit with the current
> demand.

> The API is using a consumer/provider-based model, where the providers are
> the interconnect buses and the consumers could be various drivers.
> The consumers request interconnect resources (path) between endpoints and
> set the desired constraints on this data flow path. The providers receive
> requests from consumers and aggregate these requests for all master-slave
> pairs on that path. Then the providers configure each participating in the
> topology node according to the requested data flow path, physical links
and
> constraints. The topology could be complicated and multi-tiered and is SoC
> specific.

> Signed-off-by: Georgi Djakov <[e-mail]>
> ---
>   Documentation/interconnect/interconnect.rst |  96 ++++++
>   drivers/Kconfig                             |   2 +
>   drivers/Makefile                            |   1 +
>   drivers/interconnect/Kconfig                |  10 +
>   drivers/interconnect/Makefile               |   1 +
>   drivers/interconnect/core.c                 | 489
++++++++++++++++++++++++++++
>   include/linux/interconnect-provider.h       | 109 +++++++
>   include/linux/interconnect.h                |  40 +++
>   8 files changed, 748 insertions(+)
>   create mode 100644 Documentation/interconnect/interconnect.rst
>   create mode 100644 drivers/interconnect/Kconfig
>   create mode 100644 drivers/interconnect/Makefile
>   create mode 100644 drivers/interconnect/core.c
>   create mode 100644 include/linux/interconnect-provider.h
>   create mode 100644 include/linux/interconnect.h

...
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> new file mode 100644
> index 000000000000..6306e258b9b9
> --- /dev/null
> +++ b/drivers/interconnect/core.c
> @@ -0,0 +1,489 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Interconnect framework core driver
> + *
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/idr.h>
> +#include <linux/init.h>
> +#include <linux/interconnect.h>
> +#include <linux/interconnect-provider.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +static DEFINE_IDR(icc_idr);
> +static LIST_HEAD(icc_provider_list);
> +static DEFINE_MUTEX(icc_provider_list_mutex);
> +static DEFINE_MUTEX(icc_path_mutex);
> +
> +/**
> + * struct icc_req - constraints that are attached to each node
> + *
> + * @req_node: entry in list of requests for the particular @node
> + * @node: the interconnect node to which this constraint applies
> + * @avg_bw: an integer describing the average bandwidth in kbps
> + * @peak_bw: an integer describing the peak bandwidth in kbps
> + */
> +struct icc_req {
> +       struct hlist_node req_node;
> +       struct icc_node *node;
> +       u32 avg_bw;
> +       u32 peak_bw;
> +};
> +
> +/**
> + * struct icc_path - interconnect path structure
> + * @num_nodes: number of hops (nodes)
> + * @reqs: array of the requests applicable to this path of nodes
> + */
> +struct icc_path {
> +       size_t num_nodes;
> +       struct icc_req reqs[0];
> +};
> +
> +static struct icc_node *node_find(const int id)
> +{
> +       struct icc_node *node;
> +
> +       node = idr_find(&icc_idr, id);
> +
> +       return node;
> +}
> +
> +static struct icc_path *path_allocate(struct icc_node *node, ssize_t
num_nodes)
> +{

So node is really the destination, correct? Then we use ->reverse to walk
backwards num_nodes steps towards the source. It might increase readability
to call the parameter dest, then assign that to a local called node for
traversal.

> +       struct icc_path *path;
> +       size_t i;
> +
> +       path = kzalloc(sizeof(*path) + num_nodes * sizeof(*path->reqs),
> +                      GFP_KERNEL);
> +       if (!path)
> +               return ERR_PTR(-ENOMEM);
> +
> +       path->num_nodes = num_nodes;
> +
> +       for (i = 0; i < num_nodes; i++) {
> +               hlist_add_head(&path->reqs[i].req_node, &node->req_list);
> +
> +               path->reqs[i].node = node;
> +               /* reference to previous node was saved during path
traversal */
> +               node = node->reverse;
> +       }
> +
> +       return path;
> +}
> +
> +static struct icc_path *path_find(struct icc_node *src, struct icc_node
*dst)
> +{
> +       struct icc_node *node = NULL;
> +       struct list_head traverse_list;
> +       struct list_head edge_list;
> +       struct list_head tmp_list;
> +       size_t i, number = 0;
> +       bool found = false;
> +
> +       INIT_LIST_HEAD(&traverse_list);
> +       INIT_LIST_HEAD(&edge_list);
> +       INIT_LIST_HEAD(&tmp_list);

tmp_list is really the list of nodes you've already visited and need to
remember to reset is_traversed for. Maybe calling this done_list or
visited_list would be more descriptive.

> +
> +       list_add_tail(&src->search_list, &traverse_list);

For added paranoia, you could set src->reverse to NULL so that somebody
elsewhere who had a bug in their back-traversal would fall off the end,
rather than into some previous scrapped path.

> +
> +       do {
> +               list_for_each_entry(node, &traverse_list, search_list) {
> +                       if (node == dst) {
> +                               found = true;
> +                               list_add(&node->search_list, &tmp_list);
> +                               break;
> +                       }
> +                       for (i = 0; i < node->num_links; i++) {
> +                               struct icc_node *tmp = node->links[i];
> +
> +                               if (!tmp)
> +                                       return ERR_PTR(-ENOENT);

You just bail out here, but never clean up the nodes is_traversed, which
will ruin later searches. Maybe a goto towards the common cleanup path?

> +
> +                               if (tmp->is_traversed)
> +                                       continue;
> +
> +                               tmp->is_traversed = true;
> +                               tmp->reverse = node;
> +                               list_add_tail(&tmp->search_list,
&edge_list);
> +                       }
> +               }
> +               if (found)
> +                       break;
> +
> +               list_splice_init(&traverse_list, &tmp_list);
> +               list_splice_init(&edge_list, &traverse_list);
> +
> +               /* count the number of nodes */
> +               number++;

Depth might be a better name for this, since this really counts the hops
away from the source, rather than the number of nodes you've processed.

> +
> +       } while (!list_empty(&traverse_list));
> +
> +       /* reset the traversed state */
> +       list_for_each_entry(node, &tmp_list, search_list)
> +               node->is_traversed = false;
> +
> +       if (found)
> +               return path_allocate(dst, number);
> +
> +       return ERR_PTR(-EPROBE_DEFER);
> +}
> +
> +static int path_init(struct icc_path *path)
> +{
> +       struct icc_node *node;
> +       size_t i;
> +
> +       for (i = 0; i < path->num_nodes; i++) {
> +               node = path->reqs[i].node;
> +
> +               mutex_lock(&node->provider->lock);
> +               node->provider->users++;
> +               mutex_unlock(&node->provider->lock);
> +       }
> +
> +       return 0;
> +}

This function cannot fail, nor do you check its return value, so you should
change the return type to void.

I'm wondering if the locking here is a little sketchy. I was in the process
of typing a suggestion that you call path_init from within path_find, since
it seemed weird to have this gray zone of a path without its reference
counts, when I noticed the locks.

I can't evaluate fully, since the implementation seems to be missing
icc_node_remove, a critical function in terms of evaluating the locks. You
have an icc_del_provider, but its warning of if (provider->users) is pretty
weak, since without node removal provider->users could easily be
incremented after the provider lock is released. It also leaks all of its
nodes, since there's no way to remove them.

Here's my suggestion as far as the locking goes:
* To add or remove links/nodes from the graph, you're going to need to hold
a global lock to avoid colliding with traversals. You've already got an
icc_path_mutex, so that would work.
* icc_link_create needs to hold the global icc_path_mutex, since it's
messing with arrays and connections used in path traversal, and doesn't
need to hold the provider lock, since it's not changing anything there.
* The presumably upcoming icc_link_destroy, or its parent icc_node_destroy,
also needs to hold the global lock. node_destroy may also need the provider
lock in symmetry with icc_node_add.
* Provider->users will be protected under the global icc_path_mutex, rather
than the provider lock. Then move path_init into path_find, or inline it
into path_allocate.
* Once you do that, provider->lock is now only protecting its node list.
For now, it's probably more efficient to roll the protection of
provider->nodes under the global lock as well, and remove the lock from the
provider altogether. If you anticipate other functions in the future that
will require a lock in the provider, then it might make sense to keep the
lock, or maybe just add it later with that new functionality.

> +
> +static void node_aggregate(struct icc_node *node)
> +{
> +       struct icc_req *r;
> +       u32 agg_avg = 0;
> +       u32 agg_peak = 0;
> +
> +       hlist_for_each_entry(r, &node->req_list, req_node) {
> +               /* sum(averages) and max(peaks) */
> +               agg_avg += r->avg_bw;
> +               agg_peak = max(agg_peak, r->peak_bw);
> +       }
> +
> +       node->avg_bw = agg_avg;
> +       node->peak_bw = agg_peak;
> +}
> +
> +static void provider_aggregate(struct icc_provider *provider, u32
*avg_bw,
> +                              u32 *peak_bw)
> +{
> +       struct icc_node *n;
> +       u32 agg_avg = 0;
> +       u32 agg_peak = 0;
> +
> +       /* aggregate for the interconnect provider */
> +       list_for_each_entry(n, &provider->nodes, node_list) {
> +               /* sum the average and max the peak */
> +               agg_avg += n->avg_bw;
> +               agg_peak = max(agg_peak, n->peak_bw);
> +       }
> +
> +       *avg_bw = agg_avg;
> +       *peak_bw = agg_peak;
> +}
> +
> +static int constraints_apply(struct icc_path *path)
> +{

Nit: maybe name it apply_constraints, since constraints_apply sounds like a
query (do the constraints apply?).

> +       struct icc_node *next, *prev = NULL;
> +       int i;
> +
> +       for (i = 0; i < path->num_nodes; i++, prev = next) {
> +               struct icc_provider *provider;
> +               u32 avg_bw = 0;
> +               u32 peak_bw = 0;
> +               int ret;
> +
> +               next = path->reqs[i].node;
> +               /*
> +                * Both endpoints should be valid master-slave pairs of
the
> +                * same interconnect provider that will be configured.
> +                */
> +               if (!next || !prev)
> +                       continue;
> +
> +               if (next->provider != prev->provider)
> +                       continue;

next should never be null, right? So you could shorten this to if (!prev ||
(next->provider != prev->provider))

> +
> +               provider = next->provider;
> +               mutex_lock(&provider->lock);
> +
> +               /* aggregate requests for the provider */
> +               provider_aggregate(provider, &avg_bw, &peak_bw);
> +
> +               if (provider->set) {
> +                       /* set the constraints */
> +                       ret = provider->set(prev, next, avg_bw, peak_bw);
> +               }
> +
> +               mutex_unlock(&provider->lock);
> +
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return 0;
> +}
> +
> +/**
> + * icc_set() - set constraints on an interconnect path between two
endpoints
> + * @path: reference to the path returned by icc_get()
> + * @avg_bw: average bandwidth in kbps
> + * @peak_bw: peak bandwidth in kbps
> + *
> + * This function is used by an interconnect consumer to express its own
needs
> + * in term of bandwidth and QoS for a previously requested path between
two

"in terms of" rather than "in term of", and not really QoS yet, right?

> + * endpoints. The requests are aggregated and each node is updated
accordingly.
> + *
> + * Returns 0 on success, or an approproate error code otherwise.

appropriate

> + */
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +       struct icc_node *node;
> +       size_t i;
> +       int ret;
> +
> +       if (!path)
> +               return 0;

Can we ditch this null check? My understanding is it's generally preferred
to skip this if it's only there to avoid developer errors.

> +
> +       for (i = 0; i < path->num_nodes; i++) {
> +               node = path->reqs[i].node;
> +
> +               mutex_lock(&icc_path_mutex);
> +
> +               /* update the consumer request for this path */
> +               path->reqs[i].avg_bw = avg_bw;
> +               path->reqs[i].peak_bw = peak_bw;
> +
> +               /* aggregate requests for this node */
> +               node_aggregate(node);
> +
> +               mutex_unlock(&icc_path_mutex);
> +       }
> +
> +       ret = constraints_apply(path);
> +       if (ret)
> +               pr_err("interconnect: error applying constraints (%d)",
ret);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(icc_set);
> +
> +/**
> + * icc_get() - return a handle for path between two endpoints
> + * @src_id: source device port id
> + * @dst_id: destination device port id
> + *
> + * This function will search for a path between two endpoints and return
an
> + * icc_path handle on success. Use icc_put() to release
> + * constraints when the they are not needed anymore.
> + *
> + * Return: icc_path pointer on success, or ERR_PTR() on error
> + */
> +struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +       struct icc_node *src, *dst;
> +       struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
> +
> +       src = node_find(src_id);
> +       if (!src)
> +               goto out;
> +
> +       dst = node_find(dst_id);
> +       if (!dst)
> +               goto out;
> +
> +       mutex_lock(&icc_path_mutex);
> +       path = path_find(src, dst);
> +       mutex_unlock(&icc_path_mutex);
> +       if (IS_ERR(path))
> +               goto out;
> +
> +       path_init(path);
> +
> +out:
> +       return path;
> +}
> +EXPORT_SYMBOL_GPL(icc_get);
> +
> +/**
> + * icc_put() - release the reference to the icc_path
> + * @path: interconnect path
> + *
> + * Use this function to release the constraints on a path when the path
is
> + * no longer needed. The constraints will be re-aggregated.
> + */
> +void icc_put(struct icc_path *path)
> +{
> +       struct icc_node *node;
> +       size_t i;
> +       int ret;
> +
> +       if (!path || WARN_ON_ONCE(IS_ERR(path)))
> +               return;
> +
> +       ret = icc_set(path, 0, 0);
> +       if (ret)
> +               pr_err("%s: error (%d)\n", __func__, ret);
> +
> +       for (i = 0; i < path->num_nodes; i++) {
> +               node = path->reqs[i].node;
> +               hlist_del(&path->reqs[i].req_node);
> +
> +               mutex_lock(&node->provider->lock);
> +               node->provider->users--;
> +               mutex_unlock(&node->provider->lock);
> +       }
> +
> +       kfree(path);
> +}
> +EXPORT_SYMBOL_GPL(icc_put);
> +
> +/**
> + * icc_node_create() - create a node
> + * @id: node id
> + *
> + * Return: icc_node pointer on success, or ERR_PTR() on error
> + */
> +struct icc_node *icc_node_create(int id)
> +{
> +       struct icc_node *node;
> +
> +       /* check if node already exists */
> +       node = node_find(id);
> +       if (node)
> +               return node;

This is probably going to do more harm than good once icc_node_delete comes
in, since it almost certainly indicates a programmer error or ID collision,
and will likely result in a double free. We should probably fail with
EEXIST instead.

> +
> +       node = kzalloc(sizeof(*node), GFP_KERNEL);
> +       if (!node)
> +               return ERR_PTR(-ENOMEM);
> +
> +       id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
> +       if (WARN(id < 0, "couldn't get idr"))
> +               return ERR_PTR(id);
> +
> +       node->id = id;
> +
> +       return node;
> +}
> +EXPORT_SYMBOL_GPL(icc_node_create);
> +
> +/**
> + * icc_link_create() - create a link between two nodes
> + * @src_id: source node id
> + * @dst_id: destination node id
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +       struct icc_node *dst;
> +       struct icc_node **new;
> +       int ret = 0;
> +
> +       if (IS_ERR_OR_NULL(node))
> +               return PTR_ERR(node);

Remove this.

> +
> +       mutex_lock(&node->provider->lock);
> +
> +       dst = node_find(dst_id);
> +       if (!dst)
> +               dst = icc_node_create(dst_id);

icc_node_create can fail, you should fail here if it does.

> +
> +       new = krealloc(node->links,
> +                      (node->num_links + 1) * sizeof(*node->links),
> +                      GFP_KERNEL);
> +       if (!new) {
> +               ret = -ENOMEM;
> +               goto out;
> +       }
> +
> +       node->links = new;
> +       node->links[node->num_links++] = dst;
> +
> +out:
> +       mutex_unlock(&node->provider->lock);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_link_create);
> +
> +/**
> + * icc_add_node() - add an interconnect node to interconnect provider
> + * @node: pointer to the interconnect node
> + * @provider: pointer to the interconnect provider
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +       if (WARN_ON(!node))
> +               return -EINVAL;
> +
> +       if (WARN_ON(!provider))
> +               return -EINVAL;

Remove these.

> +
> +       node->provider = provider;
> +
> +       mutex_lock(&provider->lock);
> +       list_add_tail(&node->node_list, &provider->nodes);
> +       mutex_unlock(&provider->lock);
> +
> +       return 0;
> +}

icc_node_add should be exported, right? I see it being used in msm8916.c.
You should make sure that "make allmodconfig" still builds with your
changes.

I think you should add a safety check in icc_link_create to ensure that the
node has a provider before adding any links. If some consumer made a
mistake and added links before adding the node to the provider, path
traversal would use the uninitialized or NULL provider pointer. I was
thinking about this while noticing that you assign node->provider before
acquiring the lock.

> +
> +/**
> + * icc_add_provider() - add a new interconnect provider
> + * @icc_provider: the interconnect provider that will be added into
topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_add_provider(struct icc_provider *provider)
> +{
> +       if (WARN_ON(!provider))
> +               return -EINVAL;
> +

Remove this one. The one below is okay.

> +       if (WARN_ON(!provider->set))
> +               return -EINVAL;
> +
> +       mutex_init(&provider->lock);
> +       INIT_LIST_HEAD(&provider->nodes);
> +
> +       mutex_lock(&icc_provider_list_mutex);
> +       list_add(&provider->provider_list, &icc_provider_list);
> +       mutex_unlock(&icc_provider_list_mutex);
> +
> +       dev_dbg(provider->dev, "interconnect provider added to
topology\n");
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_add_provider);
> +
> +/**
> + * icc_del_provider() - delete previously added interconnect provider
> + * @icc_provider: the interconnect provider that will be removed from
topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_del_provider(struct icc_provider *provider)
> +{
> +       mutex_lock(&provider->lock);
> +       if (provider->users) {
> +               pr_warn("interconnect provider still has %d users\n",
> +                       provider->users);
> +       }
> +       mutex_unlock(&provider->lock);
> +
> +       mutex_lock(&icc_provider_list_mutex);
> +       list_del(&provider->provider_list);
> +       mutex_unlock(&icc_provider_list_mutex);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_del_provider);
> +
> +MODULE_AUTHOR("Georgi Djakov <[e-mail]");
> +MODULE_DESCRIPTION("Interconnect Driver Core");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/interconnect-provider.h
b/include/linux/interconnect-provider.h
> new file mode 100644
> index 000000000000..779b5b5b1306
> --- /dev/null
> +++ b/include/linux/interconnect-provider.h
> @@ -0,0 +1,109 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_PROVIDER_H
> +#define _LINUX_INTERCONNECT_PROVIDER_H
> +
> +#include <linux/interconnect.h>
> +
> +struct icc_node;
> +
> +/**
> + * struct icc_provider - interconnect provider (controller) entity that
might
> + * provide multiple interconnect controls
> + *
> + * @provider_list: list of the registered interconnect providers
> + * @nodes: internal list of the interconnect provider nodes
> + * @set: pointer to device specific set operation function
> + * @dev: the device this interconnect provider belongs to
> + * @lock: lock to provide consistency during aggregation/update of
constraints
> + * @users: count of active users
> + * @data: pointer to private data
> + */
> +struct icc_provider {
> +       struct list_head        provider_list;
> +       struct list_head        nodes;
> +       int (*set)(struct icc_node *src, struct icc_node *dst,
> +                  u32 avg_bw, u32 peak_bw);
> +       struct device           *dev;
> +       struct mutex            lock;
> +       int                     users;
> +       void                    *data;
> +};
> +
> +/**
> + * struct icc_node - entity that is part of the interconnect topology
> + *
> + * @id: platform specific node id
> + * @name: node name used in debugfs
> + * @links: a list of targets where we can go next when traversing
> + * @num_links: number of links to other interconnect nodes
> + * @provider: points to the interconnect provider of this node
> + * @node_list: list of interconnect nodes associated with @provider
> + * @search_list: list used when walking the nodes graph
> + * @reverse: pointer to previous node when walking the nodes graph
> + * @is_traversed: flag that is used when walking the nodes graph
> + * @req_list: a list of QoS constraint requests associated with this node
> + * @avg_bw: aggregated value of average bandwidth
> + * @peak_bw: aggregated value of peak bandwidth
> + * @data: pointer to private data
> + */
> +struct icc_node {
> +       int                     id;

Why int here? Are you expecting negative numbers? Maybe u32 instead? Or
even better, maybe a typedef u32 icc_id? Ooh yeah, that way we know when
parameters and such are passed around that they refer to this.

> +       const char              *name;
> +       struct icc_node         **links;
> +       size_t                  num_links;
> +
> +       struct icc_provider     *provider;
> +       struct list_head        node_list;

So the difference between node_list and links is that node_list nodes live
inside this node, whereas links point at other peers?

Oh no, I get it now after reading the .c file: node_list is the list entry
in the parent provider's "nodes" list. The comment description could be
clearer about that.

-Evan

Amit Kucheria May 25, 2018, 8:26 a.m. UTC | #4

On Fri, Mar 9, 2018 at 11:09 PM, Georgi Djakov <[e-mail]> wrote:
> This patch introduce a new API to get requirements and configure the
> interconnect buses across the entire chipset to fit with the current
> demand.
>
> The API is using a consumer/provider-based model, where the providers are
> the interconnect buses and the consumers could be various drivers.
> The consumers request interconnect resources (path) between endpoints and
> set the desired constraints on this data flow path. The providers receive
> requests from consumers and aggregate these requests for all master-slave
> pairs on that path. Then the providers configure each participating in the
> topology node according to the requested data flow path, physical links and
> constraints. The topology could be complicated and multi-tiered and is SoC
> specific.
>
> Signed-off-by: Georgi Djakov <[e-mail]>
> ---
>  Documentation/interconnect/interconnect.rst |  96 ++++++
>  drivers/Kconfig                             |   2 +
>  drivers/Makefile                            |   1 +
>  drivers/interconnect/Kconfig                |  10 +
>  drivers/interconnect/Makefile               |   1 +
>  drivers/interconnect/core.c                 | 489 ++++++++++++++++++++++++++++
>  include/linux/interconnect-provider.h       | 109 +++++++
>  include/linux/interconnect.h                |  40 +++
>  8 files changed, 748 insertions(+)
>  create mode 100644 Documentation/interconnect/interconnect.rst
>  create mode 100644 drivers/interconnect/Kconfig
>  create mode 100644 drivers/interconnect/Makefile
>  create mode 100644 drivers/interconnect/core.c
>  create mode 100644 include/linux/interconnect-provider.h
>  create mode 100644 include/linux/interconnect.h
>
> diff --git a/Documentation/interconnect/interconnect.rst b/Documentation/interconnect/interconnect.rst
> new file mode 100644
> index 000000000000..23eba68e8424
> --- /dev/null
> +++ b/Documentation/interconnect/interconnect.rst
> @@ -0,0 +1,96 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=====================================
> +GENERIC SYSTEM INTERCONNECT SUBSYSTEM
> +=====================================
> +
> +Introduction
> +------------
> +
> +This framework is designed to provide a standard kernel interface to control
> +the settings of the interconnects on a SoC. These settings can be throughput,
> +latency and priority between multiple interconnected devices or functional
> +blocks. This can be controlled dynamically in order to save power or provide
> +maximum performance.
> +
> +The interconnect bus is a hardware with configurable parameters, which can be
> +set on a data path according to the requests received from various drivers.
> +An example of interconnect buses are the interconnects between various
> +components or functional blocks in chipsets. There can be multiple interconnects
> +on a SoC that can be multi-tiered.
> +
> +Below is a simplified diagram of a real-world SoC interconnect bus topology.
> +
> +::
> +
> + +----------------+    +----------------+
> + | HW Accelerator |--->|      M NoC     |<---------------+
> + +----------------+    +----------------+                |
> +                         |      |                    +------------+
> +  +-----+  +-------------+      V       +------+     |            |
> +  | DDR |  |                +--------+  | PCIe |     |            |
> +  +-----+  |                | Slaves |  +------+     |            |
> +    ^ ^    |                +--------+     |         |   C NoC    |
> +    | |    V                               V         |            |
> + +------------------+   +------------------------+   |            |   +-----+
> + |                  |-->|                        |-->|            |-->| CPU |
> + |                  |-->|                        |<--|            |   +-----+
> + |     Mem NoC      |   |         S NoC          |   +------------+
> + |                  |<--|                        |---------+    |
> + |                  |<--|                        |<------+ |    |   +--------+
> + +------------------+   +------------------------+       | |    +-->| Slaves |
> +   ^  ^    ^    ^          ^                             | |        +--------+
> +   |  |    |    |          |                             | V
> + +------+  |  +-----+   +-----+  +---------+   +----------------+   +--------+
> + | CPUs |  |  | GPU |   | DSP |  | Masters |-->|       P NoC    |-->| Slaves |
> + +------+  |  +-----+   +-----+  +---------+   +----------------+   +--------+
> +           |
> +       +-------+
> +       | Modem |
> +       +-------+
> +
> +Terminology
> +-----------
> +
> +Interconnect provider is the software definition of the interconnect hardware.
> +The interconnect providers on the above diagram are M NoC, S NoC, C NoC and Mem
> +NoC.
> +
> +Interconnect node is the software definition of the interconnect hardware
> +port. Each interconnect provider consists of multiple interconnect nodes,
> +which are connected to other SoC components including other interconnect
> +providers. The point on the diagram where the CPUs connects to the memory is
> +called an interconnect node, which belongs to the Mem NoC interconnect provider.
> +
> +Interconnect endpoints are the first or the last element of the path. Every
> +endpoint is a node, but not every node is an endpoint.
> +
> +Interconnect path is everything between two endpoints including all the nodes
> +that have to be traversed to reach from a source to destination node. It may
> +include multiple master-slave pairs across several interconnect providers.
> +
> +Interconnect consumers are the entities which make use of the data paths exposed
> +by the providers. The consumers send requests to providers requesting various
> +throughput, latency and priority. Usually the consumers are device drivers, that
> +send request based on their needs. An example for a consumer is a video decoder
> +that supports various formats and image sizes.
> +
> +Interconnect providers
> +----------------------
> +
> +Interconnect provider is an entity that implements methods to initialize and
> +configure a interconnect bus hardware. The interconnect provider drivers should
> +be registered with the interconnect provider core.
> +
> +The interconnect framework provider API functions are documented in
> +.. kernel-doc:: include/linux/interconnect-provider.h
> +
> +Interconnect consumers
> +----------------------
> +
> +Interconnect consumers are the clients which use the interconnect APIs to
> +get paths between endpoints and set their bandwidth/latency/QoS requirements
> +for these interconnect paths.
> +

This document is missing a section on the locking semantics of the
framework. Does the core ensure that the entire path is locked for
set() to propagate?

> +The interconnect framework consumer API functions are documented in
> +.. kernel-doc:: include/linux/interconnect.h
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index 879dc0604cba..96a1db022cee 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -219,4 +219,6 @@ source "drivers/siox/Kconfig"
>
>  source "drivers/slimbus/Kconfig"
>
> +source "drivers/interconnect/Kconfig"
> +
>  endmenu
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 24cd47014657..0cca95740d9b 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -185,3 +185,4 @@ obj-$(CONFIG_TEE)           += tee/
>  obj-$(CONFIG_MULTIPLEXER)      += mux/
>  obj-$(CONFIG_UNISYS_VISORBUS)  += visorbus/
>  obj-$(CONFIG_SIOX)             += siox/
> +obj-$(CONFIG_INTERCONNECT)     += interconnect/
> diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig
> new file mode 100644
> index 000000000000..a261c7d41deb
> --- /dev/null
> +++ b/drivers/interconnect/Kconfig
> @@ -0,0 +1,10 @@
> +menuconfig INTERCONNECT
> +       tristate "On-Chip Interconnect management support"
> +       help
> +         Support for management of the on-chip interconnects.
> +
> +         This framework is designed to provide a generic interface for
> +         managing the interconnects in a SoC.
> +
> +         If unsure, say no.
> +
> diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
> new file mode 100644
> index 000000000000..5edf0ae80818
> --- /dev/null
> +++ b/drivers/interconnect/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_INTERCONNECT)             += core.o
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> new file mode 100644
> index 000000000000..6306e258b9b9
> --- /dev/null
> +++ b/drivers/interconnect/core.c
> @@ -0,0 +1,489 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Interconnect framework core driver
> + *
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/idr.h>
> +#include <linux/init.h>
> +#include <linux/interconnect.h>
> +#include <linux/interconnect-provider.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +static DEFINE_IDR(icc_idr);
> +static LIST_HEAD(icc_provider_list);
> +static DEFINE_MUTEX(icc_provider_list_mutex);
> +static DEFINE_MUTEX(icc_path_mutex);
> +
> +/**
> + * struct icc_req - constraints that are attached to each node
> + *
> + * @req_node: entry in list of requests for the particular @node
> + * @node: the interconnect node to which this constraint applies
> + * @avg_bw: an integer describing the average bandwidth in kbps
> + * @peak_bw: an integer describing the peak bandwidth in kbps
> + */
> +struct icc_req {
> +       struct hlist_node req_node;
> +       struct icc_node *node;
> +       u32 avg_bw;
> +       u32 peak_bw;
> +};
> +
> +/**
> + * struct icc_path - interconnect path structure
> + * @num_nodes: number of hops (nodes)
> + * @reqs: array of the requests applicable to this path of nodes
> + */
> +struct icc_path {
> +       size_t num_nodes;
> +       struct icc_req reqs[0];
> +};
> +
> +static struct icc_node *node_find(const int id)
> +{
> +       struct icc_node *node;
> +
> +       node = idr_find(&icc_idr, id);
> +
> +       return node;
> +}
> +
> +static struct icc_path *path_allocate(struct icc_node *node, ssize_t num_nodes)
> +{
> +       struct icc_path *path;
> +       size_t i;
> +
> +       path = kzalloc(sizeof(*path) + num_nodes * sizeof(*path->reqs),
> +                      GFP_KERNEL);
> +       if (!path)
> +               return ERR_PTR(-ENOMEM);
> +
> +       path->num_nodes = num_nodes;
> +
> +       for (i = 0; i < num_nodes; i++) {
> +               hlist_add_head(&path->reqs[i].req_node, &node->req_list);
> +
> +               path->reqs[i].node = node;
> +               /* reference to previous node was saved during path traversal */
> +               node = node->reverse;
> +       }
> +
> +       return path;
> +}
> +
> +static struct icc_path *path_find(struct icc_node *src, struct icc_node *dst)
> +{
> +       struct icc_node *node = NULL;
> +       struct list_head traverse_list;
> +       struct list_head edge_list;
> +       struct list_head tmp_list;
> +       size_t i, number = 0;
> +       bool found = false;
> +
> +       INIT_LIST_HEAD(&traverse_list);
> +       INIT_LIST_HEAD(&edge_list);
> +       INIT_LIST_HEAD(&tmp_list);
> +
> +       list_add_tail(&src->search_list, &traverse_list);
> +
> +       do {
> +               list_for_each_entry(node, &traverse_list, search_list) {
> +                       if (node == dst) {
> +                               found = true;
> +                               list_add(&node->search_list, &tmp_list);
> +                               break;
> +                       }
> +                       for (i = 0; i < node->num_links; i++) {
> +                               struct icc_node *tmp = node->links[i];
> +
> +                               if (!tmp)
> +                                       return ERR_PTR(-ENOENT);
> +
> +                               if (tmp->is_traversed)
> +                                       continue;
> +
> +                               tmp->is_traversed = true;
> +                               tmp->reverse = node;
> +                               list_add_tail(&tmp->search_list, &edge_list);
> +                       }
> +               }
> +               if (found)
> +                       break;
> +
> +               list_splice_init(&traverse_list, &tmp_list);
> +               list_splice_init(&edge_list, &traverse_list);
> +
> +               /* count the number of nodes */
> +               number++;
> +
> +       } while (!list_empty(&traverse_list));
> +
> +       /* reset the traversed state */
> +       list_for_each_entry(node, &tmp_list, search_list)
> +               node->is_traversed = false;
> +
> +       if (found)
> +               return path_allocate(dst, number);
> +
> +       return ERR_PTR(-EPROBE_DEFER);
> +}
> +
> +static int path_init(struct icc_path *path)
> +{
> +       struct icc_node *node;
> +       size_t i;
> +
> +       for (i = 0; i < path->num_nodes; i++) {
> +               node = path->reqs[i].node;
> +
> +               mutex_lock(&node->provider->lock);
> +               node->provider->users++;
> +               mutex_unlock(&node->provider->lock);
> +       }
> +
> +       return 0;
> +}
> +

Consider adding some comments for node_aggregate and
provider_aggregate's aggregation algorithm

"We want the path to honor all bandwidth requests, so the average
bandwidth requirements from each consumer are aggregated at each node
and provider level. The peak bandwidth requirements will then be the
highest of all the peak bw requests"

or something to the effect that.

> +static void node_aggregate(struct icc_node *node)
> +{
> +       struct icc_req *r;
> +       u32 agg_avg = 0;
> +       u32 agg_peak = 0;
> +
> +       hlist_for_each_entry(r, &node->req_list, req_node) {
> +               /* sum(averages) and max(peaks) */
> +               agg_avg += r->avg_bw;
> +               agg_peak = max(agg_peak, r->peak_bw);
> +       }
> +
> +       node->avg_bw = agg_avg;
> +       node->peak_bw = agg_peak;
> +}
> +
> +static void provider_aggregate(struct icc_provider *provider, u32 *avg_bw,
> +                              u32 *peak_bw)
> +{
> +       struct icc_node *n;
> +       u32 agg_avg = 0;
> +       u32 agg_peak = 0;
> +
> +       /* aggregate for the interconnect provider */

You could get rid of this, the function name says as much.

> +       list_for_each_entry(n, &provider->nodes, node_list) {
> +               /* sum the average and max the peak */
> +               agg_avg += n->avg_bw;
> +               agg_peak = max(agg_peak, n->peak_bw);
> +       }
> +
> +       *avg_bw = agg_avg;
> +       *peak_bw = agg_peak;
> +}
> +
> +static int constraints_apply(struct icc_path *path)
> +{
> +       struct icc_node *next, *prev = NULL;
> +       int i;
> +
> +       for (i = 0; i < path->num_nodes; i++, prev = next) {
> +               struct icc_provider *provider;
> +               u32 avg_bw = 0;
> +               u32 peak_bw = 0;
> +               int ret;
> +
> +               next = path->reqs[i].node;
> +               /*
> +                * Both endpoints should be valid master-slave pairs of the
> +                * same interconnect provider that will be configured.
> +                */
> +               if (!next || !prev)
> +                       continue;
> +
> +               if (next->provider != prev->provider)
> +                       continue;
> +
> +               provider = next->provider;
> +               mutex_lock(&provider->lock);
> +
> +               /* aggregate requests for the provider */

Get rid of comment.

> +               provider_aggregate(provider, &avg_bw, &peak_bw);
> +
> +               if (provider->set) {
> +                       /* set the constraints */
> +                       ret = provider->set(prev, next, avg_bw, peak_bw);
> +               }
> +
> +               mutex_unlock(&provider->lock);
> +
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return 0;
> +}
> +
> +/**
> + * icc_set() - set constraints on an interconnect path between two endpoints
> + * @path: reference to the path returned by icc_get()
> + * @avg_bw: average bandwidth in kbps
> + * @peak_bw: peak bandwidth in kbps
> + *
> + * This function is used by an interconnect consumer to express its own needs
> + * in term of bandwidth and QoS for a previously requested path between two
> + * endpoints. The requests are aggregated and each node is updated accordingly.
> + *
> + * Returns 0 on success, or an approproate error code otherwise.

*appropriate*

> + */
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +       struct icc_node *node;
> +       size_t i;
> +       int ret;
> +
> +       if (!path)
> +               return 0;
> +
> +       for (i = 0; i < path->num_nodes; i++) {
> +               node = path->reqs[i].node;
> +
> +               mutex_lock(&icc_path_mutex);
> +
> +               /* update the consumer request for this path */
> +               path->reqs[i].avg_bw = avg_bw;
> +               path->reqs[i].peak_bw = peak_bw;
> +
> +               /* aggregate requests for this node */
> +               node_aggregate(node);
> +
> +               mutex_unlock(&icc_path_mutex);
> +       }
> +
> +       ret = constraints_apply(path);
> +       if (ret)
> +               pr_err("interconnect: error applying constraints (%d)", ret);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(icc_set);
> +
> +/**
> + * icc_get() - return a handle for path between two endpoints
> + * @src_id: source device port id
> + * @dst_id: destination device port id
> + *
> + * This function will search for a path between two endpoints and return an
> + * icc_path handle on success. Use icc_put() to release
> + * constraints when the they are not needed anymore.
> + *
> + * Return: icc_path pointer on success, or ERR_PTR() on error
> + */
> +struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +       struct icc_node *src, *dst;
> +       struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
> +
> +       src = node_find(src_id);
> +       if (!src)
> +               goto out;
> +
> +       dst = node_find(dst_id);
> +       if (!dst)
> +               goto out;
> +
> +       mutex_lock(&icc_path_mutex);
> +       path = path_find(src, dst);
> +       mutex_unlock(&icc_path_mutex);
> +       if (IS_ERR(path))
> +               goto out;
> +
> +       path_init(path);
> +
> +out:
> +       return path;
> +}
> +EXPORT_SYMBOL_GPL(icc_get);
> +
> +/**
> + * icc_put() - release the reference to the icc_path
> + * @path: interconnect path
> + *
> + * Use this function to release the constraints on a path when the path is
> + * no longer needed. The constraints will be re-aggregated.
> + */
> +void icc_put(struct icc_path *path)
> +{
> +       struct icc_node *node;
> +       size_t i;
> +       int ret;
> +
> +       if (!path || WARN_ON_ONCE(IS_ERR(path)))
> +               return;
> +
> +       ret = icc_set(path, 0, 0);
> +       if (ret)
> +               pr_err("%s: error (%d)\n", __func__, ret);
> +
> +       for (i = 0; i < path->num_nodes; i++) {
> +               node = path->reqs[i].node;
> +               hlist_del(&path->reqs[i].req_node);
> +
> +               mutex_lock(&node->provider->lock);
> +               node->provider->users--;
> +               mutex_unlock(&node->provider->lock);
> +       }
> +
> +       kfree(path);
> +}
> +EXPORT_SYMBOL_GPL(icc_put);
> +
> +/**
> + * icc_node_create() - create a node
> + * @id: node id
> + *
> + * Return: icc_node pointer on success, or ERR_PTR() on error
> + */
> +struct icc_node *icc_node_create(int id)
> +{
> +       struct icc_node *node;
> +
> +       /* check if node already exists */
> +       node = node_find(id);
> +       if (node)
> +               return node;
> +
> +       node = kzalloc(sizeof(*node), GFP_KERNEL);
> +       if (!node)
> +               return ERR_PTR(-ENOMEM);
> +
> +       id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
> +       if (WARN(id < 0, "couldn't get idr"))
> +               return ERR_PTR(id);
> +
> +       node->id = id;
> +
> +       return node;
> +}
> +EXPORT_SYMBOL_GPL(icc_node_create);
> +
> +/**
> + * icc_link_create() - create a link between two nodes
> + * @src_id: source node id
> + * @dst_id: destination node id
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +       struct icc_node *dst;
> +       struct icc_node **new;
> +       int ret = 0;
> +
> +       if (IS_ERR_OR_NULL(node))
> +               return PTR_ERR(node);
> +
> +       mutex_lock(&node->provider->lock);
> +
> +       dst = node_find(dst_id);
> +       if (!dst)
> +               dst = icc_node_create(dst_id);
> +
> +       new = krealloc(node->links,
> +                      (node->num_links + 1) * sizeof(*node->links),
> +                      GFP_KERNEL);
> +       if (!new) {
> +               ret = -ENOMEM;
> +               goto out;
> +       }
> +
> +       node->links = new;
> +       node->links[node->num_links++] = dst;
> +
> +out:
> +       mutex_unlock(&node->provider->lock);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_link_create);
> +
> +/**
> + * icc_add_node() - add an interconnect node to interconnect provider
> + * @node: pointer to the interconnect node
> + * @provider: pointer to the interconnect provider
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +       if (WARN_ON(!node))
> +               return -EINVAL;
> +
> +       if (WARN_ON(!provider))
> +               return -EINVAL;
> +
> +       node->provider = provider;
> +
> +       mutex_lock(&provider->lock);
> +       list_add_tail(&node->node_list, &provider->nodes);
> +       mutex_unlock(&provider->lock);
> +
> +       return 0;
> +}
> +
> +/**
> + * icc_add_provider() - add a new interconnect provider
> + * @icc_provider: the interconnect provider that will be added into topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_add_provider(struct icc_provider *provider)
> +{
> +       if (WARN_ON(!provider))
> +               return -EINVAL;
> +
> +       if (WARN_ON(!provider->set))
> +               return -EINVAL;
> +
> +       mutex_init(&provider->lock);
> +       INIT_LIST_HEAD(&provider->nodes);
> +
> +       mutex_lock(&icc_provider_list_mutex);
> +       list_add(&provider->provider_list, &icc_provider_list);
> +       mutex_unlock(&icc_provider_list_mutex);
> +
> +       dev_dbg(provider->dev, "interconnect provider added to topology\n");
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_add_provider);
> +
> +/**
> + * icc_del_provider() - delete previously added interconnect provider
> + * @icc_provider: the interconnect provider that will be removed from topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_del_provider(struct icc_provider *provider)
> +{
> +       mutex_lock(&provider->lock);
> +       if (provider->users) {
> +               pr_warn("interconnect provider still has %d users\n",
> +                       provider->users);
> +       }
> +       mutex_unlock(&provider->lock);
> +
> +       mutex_lock(&icc_provider_list_mutex);
> +       list_del(&provider->provider_list);
> +       mutex_unlock(&icc_provider_list_mutex);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_del_provider);
> +
> +MODULE_AUTHOR("Georgi Djakov <[e-mail]");
> +MODULE_DESCRIPTION("Interconnect Driver Core");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/interconnect-provider.h b/include/linux/interconnect-provider.h
> new file mode 100644
> index 000000000000..779b5b5b1306
> --- /dev/null
> +++ b/include/linux/interconnect-provider.h
> @@ -0,0 +1,109 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_PROVIDER_H
> +#define _LINUX_INTERCONNECT_PROVIDER_H
> +
> +#include <linux/interconnect.h>
> +
> +struct icc_node;
> +
> +/**
> + * struct icc_provider - interconnect provider (controller) entity that might
> + * provide multiple interconnect controls
> + *
> + * @provider_list: list of the registered interconnect providers
> + * @nodes: internal list of the interconnect provider nodes
> + * @set: pointer to device specific set operation function
> + * @dev: the device this interconnect provider belongs to
> + * @lock: lock to provide consistency during aggregation/update of constraints
> + * @users: count of active users
> + * @data: pointer to private data
> + */
> +struct icc_provider {
> +       struct list_head        provider_list;
> +       struct list_head        nodes;
> +       int (*set)(struct icc_node *src, struct icc_node *dst,
> +                  u32 avg_bw, u32 peak_bw);
> +       struct device           *dev;
> +       struct mutex            lock;
> +       int                     users;
> +       void                    *data;
> +};
> +
> +/**
> + * struct icc_node - entity that is part of the interconnect topology
> + *
> + * @id: platform specific node id
> + * @name: node name used in debugfs
> + * @links: a list of targets where we can go next when traversing
> + * @num_links: number of links to other interconnect nodes
> + * @provider: points to the interconnect provider of this node
> + * @node_list: list of interconnect nodes associated with @provider
> + * @search_list: list used when walking the nodes graph
> + * @reverse: pointer to previous node when walking the nodes graph
> + * @is_traversed: flag that is used when walking the nodes graph
> + * @req_list: a list of QoS constraint requests associated with this node


> + * @avg_bw: aggregated value of average bandwidth
> + * @peak_bw: aggregated value of peak bandwidth

Consider changing to "aggregated value of {average|peak} bandwidth
requests from all consumers"

> + * @data: pointer to private data
> + */
> +struct icc_node {
> +       int                     id;
> +       const char              *name;
> +       struct icc_node         **links;
> +       size_t                  num_links;
> +
> +       struct icc_provider     *provider;
> +       struct list_head        node_list;
> +       struct list_head        orphan_list;
> +       struct list_head        search_list;
> +       struct icc_node         *reverse;
> +       bool                    is_traversed;
> +       struct hlist_head       req_list;
> +       u32                     avg_bw;
> +       u32                     peak_bw;
> +       void                    *data;
> +};
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_node *icc_node_create(int id);
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider);
> +int icc_link_create(struct icc_node *node, const int dst_id);
> +int icc_add_provider(struct icc_provider *provider);
> +int icc_del_provider(struct icc_provider *provider);
> +
> +#else
> +
> +static inline struct icc_node *icc_node_create(int id)
> +{
> +       return ERR_PTR(-ENOTSUPP);
> +}
> +
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +       return -ENOTSUPP;
> +}
> +
> +static inline int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +       return -ENOTSUPP;
> +}
> +
> +static inline int icc_add_provider(struct icc_provider *provider)
> +{
> +       return -ENOTSUPP;
> +}
> +
> +static inline int icc_del_provider(struct icc_provider *provider)
> +{
> +       return -ENOTSUPP;
> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* _LINUX_INTERCONNECT_PROVIDER_H */
> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
> new file mode 100644
> index 000000000000..5a7cf72b76a5
> --- /dev/null
> +++ b/include/linux/interconnect.h
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_H
> +#define _LINUX_INTERCONNECT_H
> +
> +#include <linux/types.h>
> +#include <linux/mutex.h>
> +
> +struct icc_path;
> +struct device;
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_path *icc_get(const int src_id, const int dst_id);
> +void icc_put(struct icc_path *path);
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw);
> +
> +#else
> +
> +static inline struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +       return NULL;
> +}
> +
> +static inline void icc_put(struct icc_path *path)
> +{
> +}
> +
> +static inline int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +       return 0;
> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* _LINUX_INTERCONNECT_H */
>
> _______________________________________________
> linux-arm-kernel mailing list
> [e-mail]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Georgi Djakov June 6, 2018, 2:59 p.m. UTC | #5

Hi Evan,

Thanks for the detailed review!

On 12.05.18 г. 0:30, Evan Green wrote:
> Hi Georgi,
> 
> On Fri, Mar 9, 2018 at 1:12 PM Georgi Djakov <[e-mail]>
> wrote:
> 
>> This patch introduce a new API to get requirements and configure the
>> interconnect buses across the entire chipset to fit with the current
>> demand.
> 
>> The API is using a consumer/provider-based model, where the providers are
>> the interconnect buses and the consumers could be various drivers.
>> The consumers request interconnect resources (path) between endpoints and
>> set the desired constraints on this data flow path. The providers receive
>> requests from consumers and aggregate these requests for all master-slave
>> pairs on that path. Then the providers configure each participating in the
>> topology node according to the requested data flow path, physical links
> and
>> constraints. The topology could be complicated and multi-tiered and is SoC
>> specific.
> 
>> Signed-off-by: Georgi Djakov <[e-mail]>
>> ---
>>   Documentation/interconnect/interconnect.rst |  96 ++++++
>>   drivers/Kconfig                             |   2 +
>>   drivers/Makefile                            |   1 +
>>   drivers/interconnect/Kconfig                |  10 +
>>   drivers/interconnect/Makefile               |   1 +
>>   drivers/interconnect/core.c                 | 489
> ++++++++++++++++++++++++++++
>>   include/linux/interconnect-provider.h       | 109 +++++++
>>   include/linux/interconnect.h                |  40 +++
>>   8 files changed, 748 insertions(+)
>>   create mode 100644 Documentation/interconnect/interconnect.rst
>>   create mode 100644 drivers/interconnect/Kconfig
>>   create mode 100644 drivers/interconnect/Makefile
>>   create mode 100644 drivers/interconnect/core.c
>>   create mode 100644 include/linux/interconnect-provider.h
>>   create mode 100644 include/linux/interconnect.h
> 
> ...
>> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c

[..]

>> +static struct icc_path *path_allocate(struct icc_node *node, ssize_t
> num_nodes)
>> +{
> 
> So node is really the destination, correct? Then we use ->reverse to walk
> backwards num_nodes steps towards the source. It might increase readability
> to call the parameter dest, then assign that to a local called node for
> traversal.

Yes, exactly. Will change the name of the parameter to dst.

>> +       struct icc_path *path;
>> +       size_t i;
>> +
>> +       path = kzalloc(sizeof(*path) + num_nodes * sizeof(*path->reqs),
>> +                      GFP_KERNEL);
>> +       if (!path)
>> +               return ERR_PTR(-ENOMEM);
>> +
>> +       path->num_nodes = num_nodes;
>> +
>> +       for (i = 0; i < num_nodes; i++) {
>> +               hlist_add_head(&path->reqs[i].req_node, &node->req_list);
>> +
>> +               path->reqs[i].node = node;
>> +               /* reference to previous node was saved during path
> traversal */
>> +               node = node->reverse;
>> +       }
>> +
>> +       return path;
>> +}
>> +
>> +static struct icc_path *path_find(struct icc_node *src, struct icc_node
> *dst)
>> +{
>> +       struct icc_node *node = NULL;
>> +       struct list_head traverse_list;
>> +       struct list_head edge_list;
>> +       struct list_head tmp_list;
>> +       size_t i, number = 0;
>> +       bool found = false;
>> +
>> +       INIT_LIST_HEAD(&traverse_list);
>> +       INIT_LIST_HEAD(&edge_list);
>> +       INIT_LIST_HEAD(&tmp_list);
> 
> tmp_list is really the list of nodes you've already visited and need to
> remember to reset is_traversed for. Maybe calling this done_list or
> visited_list would be more descriptive.

Yes, visited_list sounds better. Will change it.

>> +
>> +       list_add_tail(&src->search_list, &traverse_list);
> 
> For added paranoia, you could set src->reverse to NULL so that somebody
> elsewhere who had a bug in their back-traversal would fall off the end,
> rather than into some previous scrapped path.

Ok.

>> +
>> +       do {
>> +               list_for_each_entry(node, &traverse_list, search_list) {
>> +                       if (node == dst) {
>> +                               found = true;
>> +                               list_add(&node->search_list, &tmp_list);
>> +                               break;
>> +                       }
>> +                       for (i = 0; i < node->num_links; i++) {
>> +                               struct icc_node *tmp = node->links[i];
>> +
>> +                               if (!tmp)
>> +                                       return ERR_PTR(-ENOENT);
> 
> You just bail out here, but never clean up the nodes is_traversed, which
> will ruin later searches. Maybe a goto towards the common cleanup path?

Agree. Good catch.

>> +
>> +                               if (tmp->is_traversed)
>> +                                       continue;
>> +
>> +                               tmp->is_traversed = true;
>> +                               tmp->reverse = node;
>> +                               list_add_tail(&tmp->search_list,
> &edge_list);
>> +                       }
>> +               }
>> +               if (found)
>> +                       break;
>> +
>> +               list_splice_init(&traverse_list, &tmp_list);
>> +               list_splice_init(&edge_list, &traverse_list);
>> +
>> +               /* count the number of nodes */
>> +               number++;
> 
> Depth might be a better name for this, since this really counts the hops
> away from the source, rather than the number of nodes you've processed.

Ok, will change it to depth.

>> +
>> +       } while (!list_empty(&traverse_list));
>> +
>> +       /* reset the traversed state */
>> +       list_for_each_entry(node, &tmp_list, search_list)
>> +               node->is_traversed = false;
>> +
>> +       if (found)
>> +               return path_allocate(dst, number);
>> +
>> +       return ERR_PTR(-EPROBE_DEFER);
>> +}
>> +
>> +static int path_init(struct icc_path *path)
>> +{
>> +       struct icc_node *node;
>> +       size_t i;
>> +
>> +       for (i = 0; i < path->num_nodes; i++) {
>> +               node = path->reqs[i].node;
>> +
>> +               mutex_lock(&node->provider->lock);
>> +               node->provider->users++;
>> +               mutex_unlock(&node->provider->lock);
>> +       }
>> +
>> +       return 0;
>> +}
> 
> This function cannot fail, nor do you check its return value, so you should
> change the return type to void.

Ok.

> 
> I'm wondering if the locking here is a little sketchy. I was in the process
> of typing a suggestion that you call path_init from within path_find, since
> it seemed weird to have this gray zone of a path without its reference
> counts, when I noticed the locks.
> 
> I can't evaluate fully, since the implementation seems to be missing
> icc_node_remove, a critical function in terms of evaluating the locks. You
> have an icc_del_provider, but its warning of if (provider->users) is pretty
> weak, since without node removal provider->users could easily be
> incremented after the provider lock is released. It also leaks all of its
> nodes, since there's no way to remove them.
> 
> Here's my suggestion as far as the locking goes:
> * To add or remove links/nodes from the graph, you're going to need to hold
> a global lock to avoid colliding with traversals. You've already got an
> icc_path_mutex, so that would work.
> * icc_link_create needs to hold the global icc_path_mutex, since it's
> messing with arrays and connections used in path traversal, and doesn't
> need to hold the provider lock, since it's not changing anything there.
> * The presumably upcoming icc_link_destroy, or its parent icc_node_destroy,
> also needs to hold the global lock. node_destroy may also need the provider
> lock in symmetry with icc_node_add.
> * Provider->users will be protected under the global icc_path_mutex, rather
> than the provider lock. Then move path_init into path_find, or inline it
> into path_allocate.
> * Once you do that, provider->lock is now only protecting its node list.
> For now, it's probably more efficient to roll the protection of
> provider->nodes under the global lock as well, and remove the lock from the
> provider altogether. If you anticipate other functions in the future that
> will require a lock in the provider, then it might make sense to keep the
> lock, or maybe just add it later with that new functionality.

Ok, i will try to simplify this. Using one global lock would be ok for
now. Will implement the complete set for functions for remove links and
nodes from the topology.

>> +
>> +static void node_aggregate(struct icc_node *node)
>> +{
>> +       struct icc_req *r;
>> +       u32 agg_avg = 0;
>> +       u32 agg_peak = 0;
>> +
>> +       hlist_for_each_entry(r, &node->req_list, req_node) {
>> +               /* sum(averages) and max(peaks) */
>> +               agg_avg += r->avg_bw;
>> +               agg_peak = max(agg_peak, r->peak_bw);
>> +       }
>> +
>> +       node->avg_bw = agg_avg;
>> +       node->peak_bw = agg_peak;
>> +}
>> +
>> +static void provider_aggregate(struct icc_provider *provider, u32
> *avg_bw,
>> +                              u32 *peak_bw)
>> +{
>> +       struct icc_node *n;
>> +       u32 agg_avg = 0;
>> +       u32 agg_peak = 0;
>> +
>> +       /* aggregate for the interconnect provider */
>> +       list_for_each_entry(n, &provider->nodes, node_list) {
>> +               /* sum the average and max the peak */
>> +               agg_avg += n->avg_bw;
>> +               agg_peak = max(agg_peak, n->peak_bw);
>> +       }
>> +
>> +       *avg_bw = agg_avg;
>> +       *peak_bw = agg_peak;
>> +}
>> +
>> +static int constraints_apply(struct icc_path *path)
>> +{
> 
> Nit: maybe name it apply_constraints, since constraints_apply sounds like a
> query (do the constraints apply?).

Ok.

>> +       struct icc_node *next, *prev = NULL;
>> +       int i;
>> +
>> +       for (i = 0; i < path->num_nodes; i++, prev = next) {
>> +               struct icc_provider *provider;
>> +               u32 avg_bw = 0;
>> +               u32 peak_bw = 0;
>> +               int ret;
>> +
>> +               next = path->reqs[i].node;
>> +               /*
>> +                * Both endpoints should be valid master-slave pairs of
> the
>> +                * same interconnect provider that will be configured.
>> +                */
>> +               if (!next || !prev)
>> +                       continue;
>> +
>> +               if (next->provider != prev->provider)
>> +                       continue;
> 
> next should never be null, right? So you could shorten this to if (!prev ||
> (next->provider != prev->provider))

Yes, right. Will do so.

>> +
>> +               provider = next->provider;
>> +               mutex_lock(&provider->lock);
>> +
>> +               /* aggregate requests for the provider */
>> +               provider_aggregate(provider, &avg_bw, &peak_bw);
>> +
>> +               if (provider->set) {
>> +                       /* set the constraints */
>> +                       ret = provider->set(prev, next, avg_bw, peak_bw);
>> +               }
>> +
>> +               mutex_unlock(&provider->lock);
>> +
>> +               if (ret)
>> +                       return ret;
>> +       }
>> +
>> +       return 0;
>> +}
>> +
>> +/**
>> + * icc_set() - set constraints on an interconnect path between two
> endpoints
>> + * @path: reference to the path returned by icc_get()
>> + * @avg_bw: average bandwidth in kbps
>> + * @peak_bw: peak bandwidth in kbps
>> + *
>> + * This function is used by an interconnect consumer to express its own
> needs
>> + * in term of bandwidth and QoS for a previously requested path between
> two
> 
> "in terms of" rather than "in term of", and not really QoS yet, right?
> 
>> + * endpoints. The requests are aggregated and each node is updated
> accordingly.
>> + *
>> + * Returns 0 on success, or an approproate error code otherwise.
> 
> appropriate
> 

Ok, thanks!

>> + */
>> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
>> +{
>> +       struct icc_node *node;
>> +       size_t i;
>> +       int ret;
>> +
>> +       if (!path)
>> +               return 0;
> 
> Can we ditch this null check? My understanding is it's generally preferred
> to skip this if it's only there to avoid developer errors.

Ok.

>> +
>> +       for (i = 0; i < path->num_nodes; i++) {
>> +               node = path->reqs[i].node;
>> +
>> +               mutex_lock(&icc_path_mutex);
>> +
>> +               /* update the consumer request for this path */
>> +               path->reqs[i].avg_bw = avg_bw;
>> +               path->reqs[i].peak_bw = peak_bw;
>> +
>> +               /* aggregate requests for this node */
>> +               node_aggregate(node);
>> +
>> +               mutex_unlock(&icc_path_mutex);
>> +       }
>> +
>> +       ret = constraints_apply(path);
>> +       if (ret)
>> +               pr_err("interconnect: error applying constraints (%d)",
> ret);
>> +
>> +       return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(icc_set);
>> +
>> +/**
>> + * icc_get() - return a handle for path between two endpoints
>> + * @src_id: source device port id
>> + * @dst_id: destination device port id
>> + *
>> + * This function will search for a path between two endpoints and return
> an
>> + * icc_path handle on success. Use icc_put() to release
>> + * constraints when the they are not needed anymore.
>> + *
>> + * Return: icc_path pointer on success, or ERR_PTR() on error
>> + */
>> +struct icc_path *icc_get(const int src_id, const int dst_id)
>> +{
>> +       struct icc_node *src, *dst;
>> +       struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
>> +
>> +       src = node_find(src_id);
>> +       if (!src)
>> +               goto out;
>> +
>> +       dst = node_find(dst_id);
>> +       if (!dst)
>> +               goto out;
>> +
>> +       mutex_lock(&icc_path_mutex);
>> +       path = path_find(src, dst);
>> +       mutex_unlock(&icc_path_mutex);
>> +       if (IS_ERR(path))
>> +               goto out;
>> +
>> +       path_init(path);
>> +
>> +out:
>> +       return path;
>> +}
>> +EXPORT_SYMBOL_GPL(icc_get);
>> +
>> +/**
>> + * icc_put() - release the reference to the icc_path
>> + * @path: interconnect path
>> + *
>> + * Use this function to release the constraints on a path when the path
> is
>> + * no longer needed. The constraints will be re-aggregated.
>> + */
>> +void icc_put(struct icc_path *path)
>> +{
>> +       struct icc_node *node;
>> +       size_t i;
>> +       int ret;
>> +
>> +       if (!path || WARN_ON_ONCE(IS_ERR(path)))
>> +               return;
>> +
>> +       ret = icc_set(path, 0, 0);
>> +       if (ret)
>> +               pr_err("%s: error (%d)\n", __func__, ret);
>> +
>> +       for (i = 0; i < path->num_nodes; i++) {
>> +               node = path->reqs[i].node;
>> +               hlist_del(&path->reqs[i].req_node);
>> +
>> +               mutex_lock(&node->provider->lock);
>> +               node->provider->users--;
>> +               mutex_unlock(&node->provider->lock);
>> +       }
>> +
>> +       kfree(path);
>> +}
>> +EXPORT_SYMBOL_GPL(icc_put);
>> +
>> +/**
>> + * icc_node_create() - create a node
>> + * @id: node id
>> + *
>> + * Return: icc_node pointer on success, or ERR_PTR() on error
>> + */
>> +struct icc_node *icc_node_create(int id)
>> +{
>> +       struct icc_node *node;
>> +
>> +       /* check if node already exists */
>> +       node = node_find(id);
>> +       if (node)
>> +               return node;
> 
> This is probably going to do more harm than good once icc_node_delete comes
> in, since it almost certainly indicates a programmer error or ID collision,
> and will likely result in a double free. We should probably fail with
> EEXIST instead.

In the current approach we create the nodes one by one, and the linked
nodes are created when they are referenced. The other way around would
be to create first all the nodes and then populate the links to avoid
the "chicken and egg" problem.

>> +
>> +       node = kzalloc(sizeof(*node), GFP_KERNEL);
>> +       if (!node)
>> +               return ERR_PTR(-ENOMEM);
>> +
>> +       id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
>> +       if (WARN(id < 0, "couldn't get idr"))
>> +               return ERR_PTR(id);
>> +
>> +       node->id = id;
>> +
>> +       return node;
>> +}
>> +EXPORT_SYMBOL_GPL(icc_node_create);
>> +
>> +/**
>> + * icc_link_create() - create a link between two nodes
>> + * @src_id: source node id
>> + * @dst_id: destination node id
>> + *
>> + * Return: 0 on success, or an error code otherwise
>> + */
>> +int icc_link_create(struct icc_node *node, const int dst_id)
>> +{
>> +       struct icc_node *dst;
>> +       struct icc_node **new;
>> +       int ret = 0;
>> +
>> +       if (IS_ERR_OR_NULL(node))
>> +               return PTR_ERR(node);
> 
> Remove this.

Ok.

>> +
>> +       mutex_lock(&node->provider->lock);
>> +
>> +       dst = node_find(dst_id);
>> +       if (!dst)
>> +               dst = icc_node_create(dst_id);
> 
> icc_node_create can fail, you should fail here if it does.

Ok.

>> +
>> +       new = krealloc(node->links,
>> +                      (node->num_links + 1) * sizeof(*node->links),
>> +                      GFP_KERNEL);
>> +       if (!new) {
>> +               ret = -ENOMEM;
>> +               goto out;
>> +       }
>> +
>> +       node->links = new;
>> +       node->links[node->num_links++] = dst;
>> +
>> +out:
>> +       mutex_unlock(&node->provider->lock);
>> +
>> +       return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(icc_link_create);
>> +
>> +/**
>> + * icc_add_node() - add an interconnect node to interconnect provider
>> + * @node: pointer to the interconnect node
>> + * @provider: pointer to the interconnect provider
>> + *
>> + * Return: 0 on success, or an error code otherwise
>> + */
>> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
>> +{
>> +       if (WARN_ON(!node))
>> +               return -EINVAL;
>> +
>> +       if (WARN_ON(!provider))
>> +               return -EINVAL;
> 
> Remove these.

Ok.

>> +
>> +       node->provider = provider;
>> +
>> +       mutex_lock(&provider->lock);
>> +       list_add_tail(&node->node_list, &provider->nodes);
>> +       mutex_unlock(&provider->lock);
>> +
>> +       return 0;
>> +}
> 
> icc_node_add should be exported, right? I see it being used in msm8916.c.
> You should make sure that "make allmodconfig" still builds with your
> changes.

Yes. Agree.

> 
> I think you should add a safety check in icc_link_create to ensure that the
> node has a provider before adding any links. If some consumer made a
> mistake and added links before adding the node to the provider, path
> traversal would use the uninitialized or NULL provider pointer. I was
> thinking about this while noticing that you assign node->provider before
> acquiring the lock.

Ok.

>> +
>> +/**
>> + * icc_add_provider() - add a new interconnect provider
>> + * @icc_provider: the interconnect provider that will be added into
> topology
>> + *
>> + * Return: 0 on success, or an error code otherwise
>> + */
>> +int icc_add_provider(struct icc_provider *provider)
>> +{
>> +       if (WARN_ON(!provider))
>> +               return -EINVAL;
>> +
> 
> Remove this one. The one below is okay.

Ok.

>> +       if (WARN_ON(!provider->set))
>> +               return -EINVAL;
>> +
>> +       mutex_init(&provider->lock);
>> +       INIT_LIST_HEAD(&provider->nodes);
>> +
>> +       mutex_lock(&icc_provider_list_mutex);
>> +       list_add(&provider->provider_list, &icc_provider_list);
>> +       mutex_unlock(&icc_provider_list_mutex);
>> +
>> +       dev_dbg(provider->dev, "interconnect provider added to
> topology\n");
>> +
>> +       return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(icc_add_provider);
>> +
>> +/**
>> + * icc_del_provider() - delete previously added interconnect provider
>> + * @icc_provider: the interconnect provider that will be removed from
> topology
>> + *
>> + * Return: 0 on success, or an error code otherwise
>> + */
>> +int icc_del_provider(struct icc_provider *provider)
>> +{
>> +       mutex_lock(&provider->lock);
>> +       if (provider->users) {
>> +               pr_warn("interconnect provider still has %d users\n",
>> +                       provider->users);
>> +       }
>> +       mutex_unlock(&provider->lock);
>> +
>> +       mutex_lock(&icc_provider_list_mutex);
>> +       list_del(&provider->provider_list);
>> +       mutex_unlock(&icc_provider_list_mutex);
>> +
>> +       return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(icc_del_provider);
>> +
>> +MODULE_AUTHOR("Georgi Djakov <[e-mail]");
>> +MODULE_DESCRIPTION("Interconnect Driver Core");
>> +MODULE_LICENSE("GPL v2");
>> diff --git a/include/linux/interconnect-provider.h
> b/include/linux/interconnect-provider.h
>> new file mode 100644
>> index 000000000000..779b5b5b1306
>> --- /dev/null
>> +++ b/include/linux/interconnect-provider.h
>> @@ -0,0 +1,109 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Copyright (c) 2018, Linaro Ltd.
>> + * Author: Georgi Djakov <[e-mail]>
>> + */
>> +
>> +#ifndef _LINUX_INTERCONNECT_PROVIDER_H
>> +#define _LINUX_INTERCONNECT_PROVIDER_H
>> +
>> +#include <linux/interconnect.h>
>> +
>> +struct icc_node;
>> +
>> +/**
>> + * struct icc_provider - interconnect provider (controller) entity that
> might
>> + * provide multiple interconnect controls
>> + *
>> + * @provider_list: list of the registered interconnect providers
>> + * @nodes: internal list of the interconnect provider nodes
>> + * @set: pointer to device specific set operation function
>> + * @dev: the device this interconnect provider belongs to
>> + * @lock: lock to provide consistency during aggregation/update of
> constraints
>> + * @users: count of active users
>> + * @data: pointer to private data
>> + */
>> +struct icc_provider {
>> +       struct list_head        provider_list;
>> +       struct list_head        nodes;
>> +       int (*set)(struct icc_node *src, struct icc_node *dst,
>> +                  u32 avg_bw, u32 peak_bw);
>> +       struct device           *dev;
>> +       struct mutex            lock;
>> +       int                     users;
>> +       void                    *data;
>> +};
>> +
>> +/**
>> + * struct icc_node - entity that is part of the interconnect topology
>> + *
>> + * @id: platform specific node id
>> + * @name: node name used in debugfs
>> + * @links: a list of targets where we can go next when traversing
>> + * @num_links: number of links to other interconnect nodes
>> + * @provider: points to the interconnect provider of this node
>> + * @node_list: list of interconnect nodes associated with @provider
>> + * @search_list: list used when walking the nodes graph
>> + * @reverse: pointer to previous node when walking the nodes graph
>> + * @is_traversed: flag that is used when walking the nodes graph
>> + * @req_list: a list of QoS constraint requests associated with this node
>> + * @avg_bw: aggregated value of average bandwidth
>> + * @peak_bw: aggregated value of peak bandwidth
>> + * @data: pointer to private data
>> + */
>> +struct icc_node {
>> +       int                     id;
> 
> Why int here? Are you expecting negative numbers? Maybe u32 instead? Or
> even better, maybe a typedef u32 icc_id? Ooh yeah, that way we know when
> parameters and such are passed around that they refer to this.

It's an int, just to be aligned with the idr API. u32 would also work.

>> +       const char              *name;
>> +       struct icc_node         **links;
>> +       size_t                  num_links;
>> +
>> +       struct icc_provider     *provider;
>> +       struct list_head        node_list;
> 
> So the difference between node_list and links is that node_list nodes live
> inside this node, whereas links point at other peers?
> 
> Oh no, I get it now after reading the .c file: node_list is the list entry
> in the parent provider's "nodes" list. The comment description could be
> clearer about that.

Ok. Will improve the wording.

Thanks,
Georgi

Georgi Djakov June 6, 2018, 3:08 p.m. UTC | #6

Hi Amit,

On 25.05.18 г. 11:26, Amit Kucheria wrote:
> On Fri, Mar 9, 2018 at 11:09 PM, Georgi Djakov <[e-mail]> wrote:
>> This patch introduce a new API to get requirements and configure the
>> interconnect buses across the entire chipset to fit with the current
>> demand.
>>
>> The API is using a consumer/provider-based model, where the providers are
>> the interconnect buses and the consumers could be various drivers.
>> The consumers request interconnect resources (path) between endpoints and
>> set the desired constraints on this data flow path. The providers receive
>> requests from consumers and aggregate these requests for all master-slave
>> pairs on that path. Then the providers configure each participating in the
>> topology node according to the requested data flow path, physical links and
>> constraints. The topology could be complicated and multi-tiered and is SoC
>> specific.
>>
>> Signed-off-by: Georgi Djakov <[e-mail]>
>> ---
[..]

>> +Interconnect consumers
>> +----------------------
>> +
>> +Interconnect consumers are the clients which use the interconnect APIs to
>> +get paths between endpoints and set their bandwidth/latency/QoS requirements
>> +for these interconnect paths.
>> +
> 
> This document is missing a section on the locking semantics of the
> framework. Does the core ensure that the entire path is locked for
> set() to propagate?

Yes, the core will ensure that the path is locked. Will add this to the
function description.

[..]

>> +
>> +static int path_init(struct icc_path *path)
>> +{
>> +       struct icc_node *node;
>> +       size_t i;
>> +
>> +       for (i = 0; i < path->num_nodes; i++) {
>> +               node = path->reqs[i].node;
>> +
>> +               mutex_lock(&node->provider->lock);
>> +               node->provider->users++;
>> +               mutex_unlock(&node->provider->lock);
>> +       }
>> +
>> +       return 0;
>> +}
>> +
> 
> Consider adding some comments for node_aggregate and
> provider_aggregate's aggregation algorithm
> 
> "We want the path to honor all bandwidth requests, so the average
> bandwidth requirements from each consumer are aggregated at each node
> and provider level. The peak bandwidth requirements will then be the
> highest of all the peak bw requests"
> 
> or something to the effect that.

Ok, thanks.

>> +static void node_aggregate(struct icc_node *node)
>> +{
>> +       struct icc_req *r;
>> +       u32 agg_avg = 0;
>> +       u32 agg_peak = 0;
>> +
>> +       hlist_for_each_entry(r, &node->req_list, req_node) {
>> +               /* sum(averages) and max(peaks) */
>> +               agg_avg += r->avg_bw;
>> +               agg_peak = max(agg_peak, r->peak_bw);
>> +       }
>> +
>> +       node->avg_bw = agg_avg;
>> +       node->peak_bw = agg_peak;
>> +}
>> +
>> +static void provider_aggregate(struct icc_provider *provider, u32 *avg_bw,
>> +                              u32 *peak_bw)
>> +{
>> +       struct icc_node *n;
>> +       u32 agg_avg = 0;
>> +       u32 agg_peak = 0;
>> +
>> +       /* aggregate for the interconnect provider */
> 
> You could get rid of this, the function name says as much.

Ok.

>> +       list_for_each_entry(n, &provider->nodes, node_list) {
>> +               /* sum the average and max the peak */
>> +               agg_avg += n->avg_bw;
>> +               agg_peak = max(agg_peak, n->peak_bw);
>> +       }
>> +
>> +       *avg_bw = agg_avg;
>> +       *peak_bw = agg_peak;
>> +}
>> +
>> +static int constraints_apply(struct icc_path *path)
>> +{
>> +       struct icc_node *next, *prev = NULL;
>> +       int i;
>> +
>> +       for (i = 0; i < path->num_nodes; i++, prev = next) {
>> +               struct icc_provider *provider;
>> +               u32 avg_bw = 0;
>> +               u32 peak_bw = 0;
>> +               int ret;
>> +
>> +               next = path->reqs[i].node;
>> +               /*
>> +                * Both endpoints should be valid master-slave pairs of the
>> +                * same interconnect provider that will be configured.
>> +                */
>> +               if (!next || !prev)
>> +                       continue;
>> +
>> +               if (next->provider != prev->provider)
>> +                       continue;
>> +
>> +               provider = next->provider;
>> +               mutex_lock(&provider->lock);
>> +
>> +               /* aggregate requests for the provider */
> 
> Get rid of comment.

Ok.

>> +               provider_aggregate(provider, &avg_bw, &peak_bw);
>> +
>> +               if (provider->set) {
>> +                       /* set the constraints */
>> +                       ret = provider->set(prev, next, avg_bw, peak_bw);
>> +               }
>> +
>> +               mutex_unlock(&provider->lock);
>> +
>> +               if (ret)
>> +                       return ret;
>> +       }
>> +
>> +       return 0;
>> +}
>> +
>> +/**
>> + * icc_set() - set constraints on an interconnect path between two endpoints
>> + * @path: reference to the path returned by icc_get()
>> + * @avg_bw: average bandwidth in kbps
>> + * @peak_bw: peak bandwidth in kbps
>> + *
>> + * This function is used by an interconnect consumer to express its own needs
>> + * in term of bandwidth and QoS for a previously requested path between two
>> + * endpoints. The requests are aggregated and each node is updated accordingly.
>> + *
>> + * Returns 0 on success, or an approproate error code otherwise.
> 
> *appropriate*

Ok.

[..]
>> +/**
>> + * struct icc_node - entity that is part of the interconnect topology
>> + *
>> + * @id: platform specific node id
>> + * @name: node name used in debugfs
>> + * @links: a list of targets where we can go next when traversing
>> + * @num_links: number of links to other interconnect nodes
>> + * @provider: points to the interconnect provider of this node
>> + * @node_list: list of interconnect nodes associated with @provider
>> + * @search_list: list used when walking the nodes graph
>> + * @reverse: pointer to previous node when walking the nodes graph
>> + * @is_traversed: flag that is used when walking the nodes graph
>> + * @req_list: a list of QoS constraint requests associated with this node
> 
> 
>> + * @avg_bw: aggregated value of average bandwidth
>> + * @peak_bw: aggregated value of peak bandwidth
> 
> Consider changing to "aggregated value of {average|peak} bandwidth
> requests from all consumers"

Ok, will clarify.

Thanks,
Georgi

Georgi Djakov June 6, 2018, 6:09 p.m. UTC | #7

Hi Evan,

On 06/06/2018 05:59 PM, Georgi Djakov wrote:
>>> +
>>> +/**
>>> + * icc_node_create() - create a node
>>> + * @id: node id
>>> + *
>>> + * Return: icc_node pointer on success, or ERR_PTR() on error
>>> + */
>>> +struct icc_node *icc_node_create(int id)
>>> +{
>>> +       struct icc_node *node;
>>> +
>>> +       /* check if node already exists */
>>> +       node = node_find(id);
>>> +       if (node)
>>> +               return node;
>>
>> This is probably going to do more harm than good once icc_node_delete comes
>> in, since it almost certainly indicates a programmer error or ID collision,
>> and will likely result in a double free. We should probably fail with
>> EEXIST instead.
> 
> In the current approach we create the nodes one by one, and the linked
> nodes are created when they are referenced. The other way around would
> be to create first all the nodes and then populate the links to avoid
> the "chicken and egg" problem.
> 

Just to elaborate a bit more on that: We can't actually register all the
nodes in advance, as we might have multiple interconnect providers
probing in different order. Each provider may have nodes linking to
nodes belonging to other providers (not probed yet). That's why we
create the nodes on the first reference and then, when the actual
provider driver is probed, the rest of the node data is filled.

Thanks,
Georgi

Evan Green June 7, 2018, 1:06 a.m. UTC | #8

On Wed, Jun 6, 2018 at 11:09 AM Georgi Djakov <[e-mail]> wrote:
>
> Hi Evan,
>
> On 06/06/2018 05:59 PM, Georgi Djakov wrote:
> >>> +
> >>> +/**
> >>> + * icc_node_create() - create a node
> >>> + * @id: node id
> >>> + *
> >>> + * Return: icc_node pointer on success, or ERR_PTR() on error
> >>> + */
> >>> +struct icc_node *icc_node_create(int id)
> >>> +{
> >>> +       struct icc_node *node;
> >>> +
> >>> +       /* check if node already exists */
> >>> +       node = node_find(id);
> >>> +       if (node)
> >>> +               return node;
> >>
> >> This is probably going to do more harm than good once icc_node_delete comes
> >> in, since it almost certainly indicates a programmer error or ID collision,
> >> and will likely result in a double free. We should probably fail with
> >> EEXIST instead.
> >
> > In the current approach we create the nodes one by one, and the linked
> > nodes are created when they are referenced. The other way around would
> > be to create first all the nodes and then populate the links to avoid
> > the "chicken and egg" problem.
> >
>
> Just to elaborate a bit more on that: We can't actually register all the
> nodes in advance, as we might have multiple interconnect providers
> probing in different order. Each provider may have nodes linking to
> nodes belonging to other providers (not probed yet). That's why we
> create the nodes on the first reference and then, when the actual
> provider driver is probed, the rest of the node data is filled.
>

Ah ok, the extra explanation helped a lot. This makes sense to me. Thanks.
-Evan

Alexandre Bailon June 8, 2018, 3:57 p.m. UTC | #9

On 03/09/2018 10:09 PM, Georgi Djakov wrote:
> This patch introduce a new API to get requirements and configure the
> interconnect buses across the entire chipset to fit with the current
> demand.
> 
> The API is using a consumer/provider-based model, where the providers are
> the interconnect buses and the consumers could be various drivers.
> The consumers request interconnect resources (path) between endpoints and
> set the desired constraints on this data flow path. The providers receive
> requests from consumers and aggregate these requests for all master-slave
> pairs on that path. Then the providers configure each participating in the
> topology node according to the requested data flow path, physical links and
> constraints. The topology could be complicated and multi-tiered and is SoC
> specific.
> 
> Signed-off-by: Georgi Djakov <[e-mail]>
> ---
>  Documentation/interconnect/interconnect.rst |  96 ++++++
>  drivers/Kconfig                             |   2 +
>  drivers/Makefile                            |   1 +
>  drivers/interconnect/Kconfig                |  10 +
>  drivers/interconnect/Makefile               |   1 +
>  drivers/interconnect/core.c                 | 489 ++++++++++++++++++++++++++++
>  include/linux/interconnect-provider.h       | 109 +++++++
>  include/linux/interconnect.h                |  40 +++
>  8 files changed, 748 insertions(+)
>  create mode 100644 Documentation/interconnect/interconnect.rst
>  create mode 100644 drivers/interconnect/Kconfig
>  create mode 100644 drivers/interconnect/Makefile
>  create mode 100644 drivers/interconnect/core.c
>  create mode 100644 include/linux/interconnect-provider.h
>  create mode 100644 include/linux/interconnect.h
> 
> diff --git a/Documentation/interconnect/interconnect.rst b/Documentation/interconnect/interconnect.rst
> new file mode 100644
> index 000000000000..23eba68e8424
> --- /dev/null
> +++ b/Documentation/interconnect/interconnect.rst
> @@ -0,0 +1,96 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=====================================
> +GENERIC SYSTEM INTERCONNECT SUBSYSTEM
> +=====================================
> +
> +Introduction
> +------------
> +
> +This framework is designed to provide a standard kernel interface to control
> +the settings of the interconnects on a SoC. These settings can be throughput,
> +latency and priority between multiple interconnected devices or functional
> +blocks. This can be controlled dynamically in order to save power or provide
> +maximum performance.
> +
> +The interconnect bus is a hardware with configurable parameters, which can be
> +set on a data path according to the requests received from various drivers.
> +An example of interconnect buses are the interconnects between various
> +components or functional blocks in chipsets. There can be multiple interconnects
> +on a SoC that can be multi-tiered.
> +
> +Below is a simplified diagram of a real-world SoC interconnect bus topology.
> +
> +::
> +
> + +----------------+    +----------------+
> + | HW Accelerator |--->|      M NoC     |<---------------+
> + +----------------+    +----------------+                |
> +                         |      |                    +------------+
> +  +-----+  +-------------+      V       +------+     |            |
> +  | DDR |  |                +--------+  | PCIe |     |            |
> +  +-----+  |                | Slaves |  +------+     |            |
> +    ^ ^    |                +--------+     |         |   C NoC    |
> +    | |    V                               V         |            |
> + +------------------+   +------------------------+   |            |   +-----+
> + |                  |-->|                        |-->|            |-->| CPU |
> + |                  |-->|                        |<--|            |   +-----+
> + |     Mem NoC      |   |         S NoC          |   +------------+
> + |                  |<--|                        |---------+    |
> + |                  |<--|                        |<------+ |    |   +--------+
> + +------------------+   +------------------------+       | |    +-->| Slaves |
> +   ^  ^    ^    ^          ^                             | |        +--------+
> +   |  |    |    |          |                             | V
> + +------+  |  +-----+   +-----+  +---------+   +----------------+   +--------+
> + | CPUs |  |  | GPU |   | DSP |  | Masters |-->|       P NoC    |-->| Slaves |
> + +------+  |  +-----+   +-----+  +---------+   +----------------+   +--------+
> +           |
> +       +-------+
> +       | Modem |
> +       +-------+
> +
> +Terminology
> +-----------
> +
> +Interconnect provider is the software definition of the interconnect hardware.
> +The interconnect providers on the above diagram are M NoC, S NoC, C NoC and Mem
> +NoC.
> +
> +Interconnect node is the software definition of the interconnect hardware
> +port. Each interconnect provider consists of multiple interconnect nodes,
> +which are connected to other SoC components including other interconnect
> +providers. The point on the diagram where the CPUs connects to the memory is
> +called an interconnect node, which belongs to the Mem NoC interconnect provider.
> +
> +Interconnect endpoints are the first or the last element of the path. Every
> +endpoint is a node, but not every node is an endpoint.
> +
> +Interconnect path is everything between two endpoints including all the nodes
> +that have to be traversed to reach from a source to destination node. It may
> +include multiple master-slave pairs across several interconnect providers.
> +
> +Interconnect consumers are the entities which make use of the data paths exposed
> +by the providers. The consumers send requests to providers requesting various
> +throughput, latency and priority. Usually the consumers are device drivers, that
> +send request based on their needs. An example for a consumer is a video decoder
> +that supports various formats and image sizes.
> +
> +Interconnect providers
> +----------------------
> +
> +Interconnect provider is an entity that implements methods to initialize and
> +configure a interconnect bus hardware. The interconnect provider drivers should
> +be registered with the interconnect provider core.
> +
> +The interconnect framework provider API functions are documented in
> +.. kernel-doc:: include/linux/interconnect-provider.h
> +
> +Interconnect consumers
> +----------------------
> +
> +Interconnect consumers are the clients which use the interconnect APIs to
> +get paths between endpoints and set their bandwidth/latency/QoS requirements
> +for these interconnect paths.
> +
> +The interconnect framework consumer API functions are documented in
> +.. kernel-doc:: include/linux/interconnect.h
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index 879dc0604cba..96a1db022cee 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -219,4 +219,6 @@ source "drivers/siox/Kconfig"
>  
>  source "drivers/slimbus/Kconfig"
>  
> +source "drivers/interconnect/Kconfig"
> +
>  endmenu
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 24cd47014657..0cca95740d9b 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -185,3 +185,4 @@ obj-$(CONFIG_TEE)		+= tee/
>  obj-$(CONFIG_MULTIPLEXER)	+= mux/
>  obj-$(CONFIG_UNISYS_VISORBUS)	+= visorbus/
>  obj-$(CONFIG_SIOX)		+= siox/
> +obj-$(CONFIG_INTERCONNECT)	+= interconnect/
> diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig
> new file mode 100644
> index 000000000000..a261c7d41deb
> --- /dev/null
> +++ b/drivers/interconnect/Kconfig
> @@ -0,0 +1,10 @@
> +menuconfig INTERCONNECT
> +	tristate "On-Chip Interconnect management support"
> +	help
> +	  Support for management of the on-chip interconnects.
> +
> +	  This framework is designed to provide a generic interface for
> +	  managing the interconnects in a SoC.
> +
> +	  If unsure, say no.
> +
> diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
> new file mode 100644
> index 000000000000..5edf0ae80818
> --- /dev/null
> +++ b/drivers/interconnect/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_INTERCONNECT)		+= core.o
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> new file mode 100644
> index 000000000000..6306e258b9b9
> --- /dev/null
> +++ b/drivers/interconnect/core.c
> @@ -0,0 +1,489 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Interconnect framework core driver
> + *
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/idr.h>
> +#include <linux/init.h>
> +#include <linux/interconnect.h>
> +#include <linux/interconnect-provider.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +static DEFINE_IDR(icc_idr);
> +static LIST_HEAD(icc_provider_list);
> +static DEFINE_MUTEX(icc_provider_list_mutex);
> +static DEFINE_MUTEX(icc_path_mutex);
> +
> +/**
> + * struct icc_req - constraints that are attached to each node
> + *
> + * @req_node: entry in list of requests for the particular @node
> + * @node: the interconnect node to which this constraint applies
> + * @avg_bw: an integer describing the average bandwidth in kbps
> + * @peak_bw: an integer describing the peak bandwidth in kbps
> + */
> +struct icc_req {
> +	struct hlist_node req_node;
> +	struct icc_node *node;
> +	u32 avg_bw;
> +	u32 peak_bw;
> +};
> +
> +/**
> + * struct icc_path - interconnect path structure
> + * @num_nodes: number of hops (nodes)
> + * @reqs: array of the requests applicable to this path of nodes
> + */
> +struct icc_path {
> +	size_t num_nodes;
> +	struct icc_req reqs[0];
> +};
> +
> +static struct icc_node *node_find(const int id)
> +{
> +	struct icc_node *node;
> +
> +	node = idr_find(&icc_idr, id);
> +
> +	return node;
> +}
> +
> +static struct icc_path *path_allocate(struct icc_node *node, ssize_t num_nodes)
> +{
> +	struct icc_path *path;
> +	size_t i;
> +
> +	path = kzalloc(sizeof(*path) + num_nodes * sizeof(*path->reqs),
> +		       GFP_KERNEL);
> +	if (!path)
> +		return ERR_PTR(-ENOMEM);
> +
> +	path->num_nodes = num_nodes;
> +
> +	for (i = 0; i < num_nodes; i++) {
> +		hlist_add_head(&path->reqs[i].req_node, &node->req_list);
> +
> +		path->reqs[i].node = node;
> +		/* reference to previous node was saved during path traversal */
> +		node = node->reverse;
> +	}
> +
> +	return path;
> +}
> +
> +static struct icc_path *path_find(struct icc_node *src, struct icc_node *dst)
> +{
> +	struct icc_node *node = NULL;
> +	struct list_head traverse_list;
> +	struct list_head edge_list;
> +	struct list_head tmp_list;
> +	size_t i, number = 0;
> +	bool found = false;
> +
> +	INIT_LIST_HEAD(&traverse_list);
> +	INIT_LIST_HEAD(&edge_list);
> +	INIT_LIST_HEAD(&tmp_list);
> +
> +	list_add_tail(&src->search_list, &traverse_list);
> +
> +	do {
> +		list_for_each_entry(node, &traverse_list, search_list) {
> +			if (node == dst) {
> +				found = true;
> +				list_add(&node->search_list, &tmp_list);
> +				break;
> +			}
> +			for (i = 0; i < node->num_links; i++) {
> +				struct icc_node *tmp = node->links[i];
> +
> +				if (!tmp)
> +					return ERR_PTR(-ENOENT);
> +
> +				if (tmp->is_traversed)
> +					continue;
> +
> +				tmp->is_traversed = true;
> +				tmp->reverse = node;
> +				list_add_tail(&tmp->search_list, &edge_list);
> +			}
> +		}
> +		if (found)
> +			break;
> +
> +		list_splice_init(&traverse_list, &tmp_list);
> +		list_splice_init(&edge_list, &traverse_list);
> +
> +		/* count the number of nodes */
> +		number++;
> +
> +	} while (!list_empty(&traverse_list));
> +
> +	/* reset the traversed state */
> +	list_for_each_entry(node, &tmp_list, search_list)
> +		node->is_traversed = false;
> +
> +	if (found)
> +		return path_allocate(dst, number);
> +
> +	return ERR_PTR(-EPROBE_DEFER);
> +}
> +
> +static int path_init(struct icc_path *path)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +
> +		mutex_lock(&node->provider->lock);
> +		node->provider->users++;
> +		mutex_unlock(&node->provider->lock);
> +	}
> +
> +	return 0;
> +}
> +
> +static void node_aggregate(struct icc_node *node)
> +{
> +	struct icc_req *r;
> +	u32 agg_avg = 0;
> +	u32 agg_peak = 0;
> +
> +	hlist_for_each_entry(r, &node->req_list, req_node) {
> +		/* sum(averages) and max(peaks) */
> +		agg_avg += r->avg_bw;
> +		agg_peak = max(agg_peak, r->peak_bw);
> +	}
> +
> +	node->avg_bw = agg_avg;
> +	node->peak_bw = agg_peak;
> +}
> +
> +static void provider_aggregate(struct icc_provider *provider, u32 *avg_bw,
> +			       u32 *peak_bw)
> +{
> +	struct icc_node *n;
> +	u32 agg_avg = 0;
> +	u32 agg_peak = 0;
> +
> +	/* aggregate for the interconnect provider */
> +	list_for_each_entry(n, &provider->nodes, node_list) {
> +		/* sum the average and max the peak */
> +		agg_avg += n->avg_bw;
> +		agg_peak = max(agg_peak, n->peak_bw);
> +	}
> +
> +	*avg_bw = agg_avg;
> +	*peak_bw = agg_peak;
> +}
> +
> +static int constraints_apply(struct icc_path *path)
> +{
> +	struct icc_node *next, *prev = NULL;
> +	int i;
> +
> +	for (i = 0; i < path->num_nodes; i++, prev = next) {
> +		struct icc_provider *provider;
> +		u32 avg_bw = 0;
> +		u32 peak_bw = 0;
> +		int ret;
> +
> +		next = path->reqs[i].node;
> +		/*
> +		 * Both endpoints should be valid master-slave pairs of the
> +		 * same interconnect provider that will be configured.
> +		 */
> +		if (!next || !prev)
> +			continue;
> +
> +		if (next->provider != prev->provider)
> +			continue;
> +
> +		provider = next->provider;
> +		mutex_lock(&provider->lock);
> +
> +		/* aggregate requests for the provider */
> +		provider_aggregate(provider, &avg_bw, &peak_bw);
> +
> +		if (provider->set) {
> +			/* set the constraints */
> +			ret = provider->set(prev, next, avg_bw, peak_bw);
> +		}
> +
> +		mutex_unlock(&provider->lock);
> +
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * icc_set() - set constraints on an interconnect path between two endpoints
> + * @path: reference to the path returned by icc_get()
> + * @avg_bw: average bandwidth in kbps
> + * @peak_bw: peak bandwidth in kbps
> + *
> + * This function is used by an interconnect consumer to express its own needs
> + * in term of bandwidth and QoS for a previously requested path between two
> + * endpoints. The requests are aggregated and each node is updated accordingly.
> + *
> + * Returns 0 on success, or an approproate error code otherwise.
> + */
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +	int ret;
> +
> +	if (!path)
> +		return 0;
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +
> +		mutex_lock(&icc_path_mutex);
> +
> +		/* update the consumer request for this path */
> +		path->reqs[i].avg_bw = avg_bw;
> +		path->reqs[i].peak_bw = peak_bw;
> +
> +		/* aggregate requests for this node */
> +		node_aggregate(node);
> +
> +		mutex_unlock(&icc_path_mutex);
> +	}
> +
> +	ret = constraints_apply(path);
> +	if (ret)
> +		pr_err("interconnect: error applying constraints (%d)", ret);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(icc_set);
> +
> +/**
> + * icc_get() - return a handle for path between two endpoints
> + * @src_id: source device port id
> + * @dst_id: destination device port id
> + *
> + * This function will search for a path between two endpoints and return an
> + * icc_path handle on success. Use icc_put() to release
> + * constraints when the they are not needed anymore.
> + *
> + * Return: icc_path pointer on success, or ERR_PTR() on error
> + */
> +struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +	struct icc_node *src, *dst;
> +	struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
> +
> +	src = node_find(src_id);
> +	if (!src)
> +		goto out;
> +
> +	dst = node_find(dst_id);
> +	if (!dst)
> +		goto out;
> +
> +	mutex_lock(&icc_path_mutex);
> +	path = path_find(src, dst);
> +	mutex_unlock(&icc_path_mutex);
> +	if (IS_ERR(path))
> +		goto out;
> +
> +	path_init(path);
> +
> +out:
> +	return path;
> +}
> +EXPORT_SYMBOL_GPL(icc_get);
> +
> +/**
> + * icc_put() - release the reference to the icc_path
> + * @path: interconnect path
> + *
> + * Use this function to release the constraints on a path when the path is
> + * no longer needed. The constraints will be re-aggregated.
> + */
> +void icc_put(struct icc_path *path)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +	int ret;
> +
> +	if (!path || WARN_ON_ONCE(IS_ERR(path)))
> +		return;
> +
> +	ret = icc_set(path, 0, 0);
> +	if (ret)
> +		pr_err("%s: error (%d)\n", __func__, ret);
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +		hlist_del(&path->reqs[i].req_node);
> +
> +		mutex_lock(&node->provider->lock);
> +		node->provider->users--;
> +		mutex_unlock(&node->provider->lock);
> +	}
> +
> +	kfree(path);
> +}
> +EXPORT_SYMBOL_GPL(icc_put);
> +
> +/**
> + * icc_node_create() - create a node
> + * @id: node id
> + *
> + * Return: icc_node pointer on success, or ERR_PTR() on error
> + */
> +struct icc_node *icc_node_create(int id)
> +{
> +	struct icc_node *node;
> +
> +	/* check if node already exists */
> +	node = node_find(id);
> +	if (node)
> +		return node;
> +
> +	node = kzalloc(sizeof(*node), GFP_KERNEL);
> +	if (!node)
> +		return ERR_PTR(-ENOMEM);
> +
> +	id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
> +	if (WARN(id < 0, "couldn't get idr"))
> +		return ERR_PTR(id);
> +
> +	node->id = id;
> +
> +	return node;
> +}
> +EXPORT_SYMBOL_GPL(icc_node_create);
> +
> +/**
> + * icc_link_create() - create a link between two nodes
> + * @src_id: source node id
I guess src_id has become node and is not an id anymore,
so it should be updated.
> + * @dst_id: destination node id
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +	struct icc_node *dst;
> +	struct icc_node **new;
> +	int ret = 0;
> +
> +	if (IS_ERR_OR_NULL(node))
> +		return PTR_ERR(node);
> +
> +	mutex_lock(&node->provider->lock);
> +
> +	dst = node_find(dst_id);
> +	if (!dst)
> +		dst = icc_node_create(dst_id);
> +
> +	new = krealloc(node->links,
> +		       (node->num_links + 1) * sizeof(*node->links),
> +		       GFP_KERNEL);
> +	if (!new) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	node->links = new;
> +	node->links[node->num_links++] = dst;
> +
> +out:
> +	mutex_unlock(&node->provider->lock);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_link_create);
> +
> +/**
> + * icc_add_node() - add an interconnect node to interconnect provider
> + * @node: pointer to the interconnect node
> + * @provider: pointer to the interconnect provider
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +	if (WARN_ON(!node))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!provider))
> +		return -EINVAL;
> +
> +	node->provider = provider;
> +
> +	mutex_lock(&provider->lock);
> +	list_add_tail(&node->node_list, &provider->nodes);
> +	mutex_unlock(&provider->lock);
> +
> +	return 0;
> +}
> +
> +/**
> + * icc_add_provider() - add a new interconnect provider
> + * @icc_provider: the interconnect provider that will be added into topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_add_provider(struct icc_provider *provider)
> +{
> +	if (WARN_ON(!provider))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!provider->set))
> +		return -EINVAL;
> +
> +	mutex_init(&provider->lock);
> +	INIT_LIST_HEAD(&provider->nodes);
> +
> +	mutex_lock(&icc_provider_list_mutex);
> +	list_add(&provider->provider_list, &icc_provider_list);
> +	mutex_unlock(&icc_provider_list_mutex);
> +
> +	dev_dbg(provider->dev, "interconnect provider added to topology\n");
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_add_provider);
> +
> +/**
> + * icc_del_provider() - delete previously added interconnect provider
> + * @icc_provider: the interconnect provider that will be removed from topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_del_provider(struct icc_provider *provider)
> +{
> +	mutex_lock(&provider->lock);
> +	if (provider->users) {
> +		pr_warn("interconnect provider still has %d users\n",
> +			provider->users);
> +	}
> +	mutex_unlock(&provider->lock);
> +
> +	mutex_lock(&icc_provider_list_mutex);
> +	list_del(&provider->provider_list);
> +	mutex_unlock(&icc_provider_list_mutex);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_del_provider);
> +
> +MODULE_AUTHOR("Georgi Djakov <[e-mail]");
> +MODULE_DESCRIPTION("Interconnect Driver Core");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/interconnect-provider.h b/include/linux/interconnect-provider.h
> new file mode 100644
> index 000000000000..779b5b5b1306
> --- /dev/null
> +++ b/include/linux/interconnect-provider.h
> @@ -0,0 +1,109 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_PROVIDER_H
> +#define _LINUX_INTERCONNECT_PROVIDER_H
> +
> +#include <linux/interconnect.h>
> +
> +struct icc_node;
> +
> +/**
> + * struct icc_provider - interconnect provider (controller) entity that might
> + * provide multiple interconnect controls
> + *
> + * @provider_list: list of the registered interconnect providers
> + * @nodes: internal list of the interconnect provider nodes
> + * @set: pointer to device specific set operation function
> + * @dev: the device this interconnect provider belongs to
> + * @lock: lock to provide consistency during aggregation/update of constraints
> + * @users: count of active users
> + * @data: pointer to private data
> + */
> +struct icc_provider {
> +	struct list_head	provider_list;
> +	struct list_head	nodes;
> +	int (*set)(struct icc_node *src, struct icc_node *dst,
> +		   u32 avg_bw, u32 peak_bw);
> +	struct device		*dev;
> +	struct mutex		lock;
> +	int			users;
> +	void			*data;
> +};
> +
> +/**
> + * struct icc_node - entity that is part of the interconnect topology
> + *
> + * @id: platform specific node id
> + * @name: node name used in debugfs
> + * @links: a list of targets where we can go next when traversing
> + * @num_links: number of links to other interconnect nodes
> + * @provider: points to the interconnect provider of this node
> + * @node_list: list of interconnect nodes associated with @provider
> + * @search_list: list used when walking the nodes graph
> + * @reverse: pointer to previous node when walking the nodes graph
> + * @is_traversed: flag that is used when walking the nodes graph
> + * @req_list: a list of QoS constraint requests associated with this node
> + * @avg_bw: aggregated value of average bandwidth
> + * @peak_bw: aggregated value of peak bandwidth
> + * @data: pointer to private data
> + */
> +struct icc_node {
> +	int			id;
> +	const char              *name;
> +	struct icc_node		**links;
> +	size_t			num_links;
> +
> +	struct icc_provider	*provider;
> +	struct list_head	node_list;
> +	struct list_head	orphan_list;
> +	struct list_head	search_list;
> +	struct icc_node		*reverse;
> +	bool			is_traversed;
> +	struct hlist_head	req_list;
> +	u32			avg_bw;
> +	u32			peak_bw;
> +	void			*data;
> +};
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_node *icc_node_create(int id);
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider);
> +int icc_link_create(struct icc_node *node, const int dst_id);
> +int icc_add_provider(struct icc_provider *provider);
> +int icc_del_provider(struct icc_provider *provider);
> +
> +#else
> +
> +static inline struct icc_node *icc_node_create(int id)
> +{
> +	return ERR_PTR(-ENOTSUPP);
> +}
> +
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_add_provider(struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_del_provider(struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* _LINUX_INTERCONNECT_PROVIDER_H */
> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
> new file mode 100644
> index 000000000000..5a7cf72b76a5
> --- /dev/null
> +++ b/include/linux/interconnect.h
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[e-mail]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_H
> +#define _LINUX_INTERCONNECT_H
> +
> +#include <linux/types.h>
> +#include <linux/mutex.h>
> +
> +struct icc_path;
> +struct device;
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_path *icc_get(const int src_id, const int dst_id);
> +void icc_put(struct icc_path *path);
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw);
> +
> +#else
> +
> +static inline struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +	return NULL;
> +}
> +
> +static inline void icc_put(struct icc_path *path)
> +{
> +}
> +
> +static inline int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +	return 0;
> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* _LINUX_INTERCONNECT_H */
>

Georgi Djakov June 9, 2018, 7:15 p.m. UTC | #10

Hi Alexandre,

On 8.06.18 г. 18:57, Alexandre Bailon wrote:
> On 03/09/2018 10:09 PM, Georgi Djakov wrote:
>> This patch introduce a new API to get requirements and configure the
>> interconnect buses across the entire chipset to fit with the current
>> demand.
>>
>> The API is using a consumer/provider-based model, where the providers are
>> the interconnect buses and the consumers could be various drivers.
>> The consumers request interconnect resources (path) between endpoints and
>> set the desired constraints on this data flow path. The providers receive
>> requests from consumers and aggregate these requests for all master-slave
>> pairs on that path. Then the providers configure each participating in the
>> topology node according to the requested data flow path, physical links and
>> constraints. The topology could be complicated and multi-tiered and is SoC
>> specific.
>>
>> Signed-off-by: Georgi Djakov <[e-mail]>
>> ---
>>  Documentation/interconnect/interconnect.rst |  96 ++++++
>>  drivers/Kconfig                             |   2 +
>>  drivers/Makefile                            |   1 +
>>  drivers/interconnect/Kconfig                |  10 +
>>  drivers/interconnect/Makefile               |   1 +
>>  drivers/interconnect/core.c                 | 489 ++++++++++++++++++++++++++++
>>  include/linux/interconnect-provider.h       | 109 +++++++
>>  include/linux/interconnect.h                |  40 +++
>>  8 files changed, 748 insertions(+)
>>  create mode 100644 Documentation/interconnect/interconnect.rst
>>  create mode 100644 drivers/interconnect/Kconfig
>>  create mode 100644 drivers/interconnect/Makefile
>>  create mode 100644 drivers/interconnect/core.c
>>  create mode 100644 include/linux/interconnect-provider.h
>>  create mode 100644 include/linux/interconnect.h
>>

[..]

>> +
>> +/**
>> + * icc_link_create() - create a link between two nodes
>> + * @src_id: source node id
> I guess src_id has become node and is not an id anymore,
> so it should be updated.

Yes, absolutely!

>> + * @dst_id: destination node id
>> + *
>> + * Return: 0 on success, or an error code otherwise
>> + */
>> +int icc_link_create(struct icc_node *node, const int dst_id)
>> +{

Thanks,
Georgi

Patch

diff --git a/Documentation/interconnect/interconnect.rst b/Documentation/interconnect/interconnect.rst
new file mode 100644
index 000000000000..23eba68e8424
--- /dev/null
+++ b/Documentation/interconnect/interconnect.rst
@@ -0,0 +1,96 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================================
+GENERIC SYSTEM INTERCONNECT SUBSYSTEM
+=====================================
+
+Introduction
+------------
+
+This framework is designed to provide a standard kernel interface to control
+the settings of the interconnects on a SoC. These settings can be throughput,
+latency and priority between multiple interconnected devices or functional
+blocks. This can be controlled dynamically in order to save power or provide
+maximum performance.
+
+The interconnect bus is a hardware with configurable parameters, which can be
+set on a data path according to the requests received from various drivers.
+An example of interconnect buses are the interconnects between various
+components or functional blocks in chipsets. There can be multiple interconnects
+on a SoC that can be multi-tiered.
+
+Below is a simplified diagram of a real-world SoC interconnect bus topology.
+
+::
+
+ +----------------+    +----------------+
+ | HW Accelerator |--->|      M NoC     |<---------------+
+ +----------------+    +----------------+                |
+                         |      |                    +------------+
+  +-----+  +-------------+      V       +------+     |            |
+  | DDR |  |                +--------+  | PCIe |     |            |
+  +-----+  |                | Slaves |  +------+     |            |
+    ^ ^    |                +--------+     |         |   C NoC    |
+    | |    V                               V         |            |
+ +------------------+   +------------------------+   |            |   +-----+
+ |                  |-->|                        |-->|            |-->| CPU |
+ |                  |-->|                        |<--|            |   +-----+
+ |     Mem NoC      |   |         S NoC          |   +------------+
+ |                  |<--|                        |---------+    |
+ |                  |<--|                        |<------+ |    |   +--------+
+ +------------------+   +------------------------+       | |    +-->| Slaves |
+   ^  ^    ^    ^          ^                             | |        +--------+
+   |  |    |    |          |                             | V
+ +------+  |  +-----+   +-----+  +---------+   +----------------+   +--------+
+ | CPUs |  |  | GPU |   | DSP |  | Masters |-->|       P NoC    |-->| Slaves |
+ +------+  |  +-----+   +-----+  +---------+   +----------------+   +--------+
+           |
+       +-------+
+       | Modem |
+       +-------+
+
+Terminology
+-----------
+
+Interconnect provider is the software definition of the interconnect hardware.
+The interconnect providers on the above diagram are M NoC, S NoC, C NoC and Mem
+NoC.
+
+Interconnect node is the software definition of the interconnect hardware
+port. Each interconnect provider consists of multiple interconnect nodes,
+which are connected to other SoC components including other interconnect
+providers. The point on the diagram where the CPUs connects to the memory is
+called an interconnect node, which belongs to the Mem NoC interconnect provider.
+
+Interconnect endpoints are the first or the last element of the path. Every
+endpoint is a node, but not every node is an endpoint.
+
+Interconnect path is everything between two endpoints including all the nodes
+that have to be traversed to reach from a source to destination node. It may
+include multiple master-slave pairs across several interconnect providers.
+
+Interconnect consumers are the entities which make use of the data paths exposed
+by the providers. The consumers send requests to providers requesting various
+throughput, latency and priority. Usually the consumers are device drivers, that
+send request based on their needs. An example for a consumer is a video decoder
+that supports various formats and image sizes.
+
+Interconnect providers
+----------------------
+
+Interconnect provider is an entity that implements methods to initialize and
+configure a interconnect bus hardware. The interconnect provider drivers should
+be registered with the interconnect provider core.
+
+The interconnect framework provider API functions are documented in
+.. kernel-doc:: include/linux/interconnect-provider.h
+
+Interconnect consumers
+----------------------
+
+Interconnect consumers are the clients which use the interconnect APIs to
+get paths between endpoints and set their bandwidth/latency/QoS requirements
+for these interconnect paths.
+
+The interconnect framework consumer API functions are documented in
+.. kernel-doc:: include/linux/interconnect.h
diff --git a/drivers/Kconfig b/drivers/Kconfig
index 879dc0604cba..96a1db022cee 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -219,4 +219,6 @@  source "drivers/siox/Kconfig"
 
 source "drivers/slimbus/Kconfig"
 
+source "drivers/interconnect/Kconfig"
+
 endmenu
diff --git a/drivers/Makefile b/drivers/Makefile
index 24cd47014657..0cca95740d9b 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -185,3 +185,4 @@  obj-$(CONFIG_TEE)		+= tee/
 obj-$(CONFIG_MULTIPLEXER)	+= mux/
 obj-$(CONFIG_UNISYS_VISORBUS)	+= visorbus/
 obj-$(CONFIG_SIOX)		+= siox/
+obj-$(CONFIG_INTERCONNECT)	+= interconnect/
diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig
new file mode 100644
index 000000000000..a261c7d41deb
--- /dev/null
+++ b/drivers/interconnect/Kconfig
@@ -0,0 +1,10 @@ 
+menuconfig INTERCONNECT
+	tristate "On-Chip Interconnect management support"
+	help
+	  Support for management of the on-chip interconnects.
+
+	  This framework is designed to provide a generic interface for
+	  managing the interconnects in a SoC.
+
+	  If unsure, say no.
+
diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
new file mode 100644
index 000000000000..5edf0ae80818
--- /dev/null
+++ b/drivers/interconnect/Makefile
@@ -0,0 +1 @@ 
+obj-$(CONFIG_INTERCONNECT)		+= core.o
diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
new file mode 100644
index 000000000000..6306e258b9b9
--- /dev/null
+++ b/drivers/interconnect/core.c
@@ -0,0 +1,489 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Interconnect framework core driver
+ *
+ * Copyright (c) 2018, Linaro Ltd.
+ * Author: Georgi Djakov <[e-mail]>
+ */
+
+#include <linux/device.h>
+#include <linux/idr.h>
+#include <linux/init.h>
+#include <linux/interconnect.h>
+#include <linux/interconnect-provider.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+
+static DEFINE_IDR(icc_idr);
+static LIST_HEAD(icc_provider_list);
+static DEFINE_MUTEX(icc_provider_list_mutex);
+static DEFINE_MUTEX(icc_path_mutex);
+
+/**
+ * struct icc_req - constraints that are attached to each node
+ *
+ * @req_node: entry in list of requests for the particular @node
+ * @node: the interconnect node to which this constraint applies
+ * @avg_bw: an integer describing the average bandwidth in kbps
+ * @peak_bw: an integer describing the peak bandwidth in kbps
+ */
+struct icc_req {
+	struct hlist_node req_node;
+	struct icc_node *node;
+	u32 avg_bw;
+	u32 peak_bw;
+};
+
+/**
+ * struct icc_path - interconnect path structure
+ * @num_nodes: number of hops (nodes)
+ * @reqs: array of the requests applicable to this path of nodes
+ */
+struct icc_path {
+	size_t num_nodes;
+	struct icc_req reqs[0];
+};
+
+static struct icc_node *node_find(const int id)
+{
+	struct icc_node *node;
+
+	node = idr_find(&icc_idr, id);
+
+	return node;
+}
+
+static struct icc_path *path_allocate(struct icc_node *node, ssize_t num_nodes)
+{
+	struct icc_path *path;
+	size_t i;
+
+	path = kzalloc(sizeof(*path) + num_nodes * sizeof(*path->reqs),
+		       GFP_KERNEL);
+	if (!path)
+		return ERR_PTR(-ENOMEM);
+
+	path->num_nodes = num_nodes;
+
+	for (i = 0; i < num_nodes; i++) {
+		hlist_add_head(&path->reqs[i].req_node, &node->req_list);
+
+		path->reqs[i].node = node;
+		/* reference to previous node was saved during path traversal */
+		node = node->reverse;
+	}
+
+	return path;
+}
+
+static struct icc_path *path_find(struct icc_node *src, struct icc_node *dst)
+{
+	struct icc_node *node = NULL;
+	struct list_head traverse_list;
+	struct list_head edge_list;
+	struct list_head tmp_list;
+	size_t i, number = 0;
+	bool found = false;
+
+	INIT_LIST_HEAD(&traverse_list);
+	INIT_LIST_HEAD(&edge_list);
+	INIT_LIST_HEAD(&tmp_list);
+
+	list_add_tail(&src->search_list, &traverse_list);
+
+	do {
+		list_for_each_entry(node, &traverse_list, search_list) {
+			if (node == dst) {
+				found = true;
+				list_add(&node->search_list, &tmp_list);
+				break;
+			}
+			for (i = 0; i < node->num_links; i++) {
+				struct icc_node *tmp = node->links[i];
+
+				if (!tmp)
+					return ERR_PTR(-ENOENT);
+
+				if (tmp->is_traversed)
+					continue;
+
+				tmp->is_traversed = true;
+				tmp->reverse = node;
+				list_add_tail(&tmp->search_list, &edge_list);
+			}
+		}
+		if (found)
+			break;
+
+		list_splice_init(&traverse_list, &tmp_list);
+		list_splice_init(&edge_list, &traverse_list);
+
+		/* count the number of nodes */
+		number++;
+
+	} while (!list_empty(&traverse_list));
+
+	/* reset the traversed state */
+	list_for_each_entry(node, &tmp_list, search_list)
+		node->is_traversed = false;
+
+	if (found)
+		return path_allocate(dst, number);
+
+	return ERR_PTR(-EPROBE_DEFER);
+}
+
+static int path_init(struct icc_path *path)
+{
+	struct icc_node *node;
+	size_t i;
+
+	for (i = 0; i < path->num_nodes; i++) {
+		node = path->reqs[i].node;
+
+		mutex_lock(&node->provider->lock);
+		node->provider->users++;
+		mutex_unlock(&node->provider->lock);
+	}
+
+	return 0;
+}
+
+static void node_aggregate(struct icc_node *node)
+{
+	struct icc_req *r;
+	u32 agg_avg = 0;
+	u32 agg_peak = 0;
+
+	hlist_for_each_entry(r, &node->req_list, req_node) {
+		/* sum(averages) and max(peaks) */
+		agg_avg += r->avg_bw;
+		agg_peak = max(agg_peak, r->peak_bw);
+	}
+
+	node->avg_bw = agg_avg;
+	node->peak_bw = agg_peak;
+}
+
+static void provider_aggregate(struct icc_provider *provider, u32 *avg_bw,
+			       u32 *peak_bw)
+{
+	struct icc_node *n;
+	u32 agg_avg = 0;
+	u32 agg_peak = 0;
+
+	/* aggregate for the interconnect provider */
+	list_for_each_entry(n, &provider->nodes, node_list) {
+		/* sum the average and max the peak */
+		agg_avg += n->avg_bw;
+		agg_peak = max(agg_peak, n->peak_bw);
+	}
+
+	*avg_bw = agg_avg;
+	*peak_bw = agg_peak;
+}
+
+static int constraints_apply(struct icc_path *path)
+{
+	struct icc_node *next, *prev = NULL;
+	int i;
+
+	for (i = 0; i < path->num_nodes; i++, prev = next) {
+		struct icc_provider *provider;
+		u32 avg_bw = 0;
+		u32 peak_bw = 0;
+		int ret;
+
+		next = path->reqs[i].node;
+		/*
+		 * Both endpoints should be valid master-slave pairs of the
+		 * same interconnect provider that will be configured.
+		 */
+		if (!next || !prev)
+			continue;
+
+		if (next->provider != prev->provider)
+			continue;
+
+		provider = next->provider;
+		mutex_lock(&provider->lock);
+
+		/* aggregate requests for the provider */
+		provider_aggregate(provider, &avg_bw, &peak_bw);
+
+		if (provider->set) {
+			/* set the constraints */
+			ret = provider->set(prev, next, avg_bw, peak_bw);
+		}
+
+		mutex_unlock(&provider->lock);
+
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+/**
+ * icc_set() - set constraints on an interconnect path between two endpoints
+ * @path: reference to the path returned by icc_get()
+ * @avg_bw: average bandwidth in kbps
+ * @peak_bw: peak bandwidth in kbps
+ *
+ * This function is used by an interconnect consumer to express its own needs
+ * in term of bandwidth and QoS for a previously requested path between two
+ * endpoints. The requests are aggregated and each node is updated accordingly.
+ *
+ * Returns 0 on success, or an approproate error code otherwise.
+ */
+int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
+{
+	struct icc_node *node;
+	size_t i;
+	int ret;
+
+	if (!path)
+		return 0;
+
+	for (i = 0; i < path->num_nodes; i++) {
+		node = path->reqs[i].node;
+
+		mutex_lock(&icc_path_mutex);
+
+		/* update the consumer request for this path */
+		path->reqs[i].avg_bw = avg_bw;
+		path->reqs[i].peak_bw = peak_bw;
+
+		/* aggregate requests for this node */
+		node_aggregate(node);
+
+		mutex_unlock(&icc_path_mutex);
+	}
+
+	ret = constraints_apply(path);
+	if (ret)
+		pr_err("interconnect: error applying constraints (%d)", ret);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(icc_set);
+
+/**
+ * icc_get() - return a handle for path between two endpoints
+ * @src_id: source device port id
+ * @dst_id: destination device port id
+ *
+ * This function will search for a path between two endpoints and return an
+ * icc_path handle on success. Use icc_put() to release
+ * constraints when the they are not needed anymore.
+ *
+ * Return: icc_path pointer on success, or ERR_PTR() on error
+ */
+struct icc_path *icc_get(const int src_id, const int dst_id)
+{
+	struct icc_node *src, *dst;
+	struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
+
+	src = node_find(src_id);
+	if (!src)
+		goto out;
+
+	dst = node_find(dst_id);
+	if (!dst)
+		goto out;
+
+	mutex_lock(&icc_path_mutex);
+	path = path_find(src, dst);
+	mutex_unlock(&icc_path_mutex);
+	if (IS_ERR(path))
+		goto out;
+
+	path_init(path);
+
+out:
+	return path;
+}
+EXPORT_SYMBOL_GPL(icc_get);
+
+/**
+ * icc_put() - release the reference to the icc_path
+ * @path: interconnect path
+ *
+ * Use this function to release the constraints on a path when the path is
+ * no longer needed. The constraints will be re-aggregated.
+ */
+void icc_put(struct icc_path *path)
+{
+	struct icc_node *node;
+	size_t i;
+	int ret;
+
+	if (!path || WARN_ON_ONCE(IS_ERR(path)))
+		return;
+
+	ret = icc_set(path, 0, 0);
+	if (ret)
+		pr_err("%s: error (%d)\n", __func__, ret);
+
+	for (i = 0; i < path->num_nodes; i++) {
+		node = path->reqs[i].node;
+		hlist_del(&path->reqs[i].req_node);
+
+		mutex_lock(&node->provider->lock);
+		node->provider->users--;
+		mutex_unlock(&node->provider->lock);
+	}
+
+	kfree(path);
+}
+EXPORT_SYMBOL_GPL(icc_put);
+
+/**
+ * icc_node_create() - create a node
+ * @id: node id
+ *
+ * Return: icc_node pointer on success, or ERR_PTR() on error
+ */
+struct icc_node *icc_node_create(int id)
+{
+	struct icc_node *node;
+
+	/* check if node already exists */
+	node = node_find(id);
+	if (node)
+		return node;
+
+	node = kzalloc(sizeof(*node), GFP_KERNEL);
+	if (!node)
+		return ERR_PTR(-ENOMEM);
+
+	id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
+	if (WARN(id < 0, "couldn't get idr"))
+		return ERR_PTR(id);
+
+	node->id = id;
+
+	return node;
+}
+EXPORT_SYMBOL_GPL(icc_node_create);
+
+/**
+ * icc_link_create() - create a link between two nodes
+ * @src_id: source node id
+ * @dst_id: destination node id
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_link_create(struct icc_node *node, const int dst_id)
+{
+	struct icc_node *dst;
+	struct icc_node **new;
+	int ret = 0;
+
+	if (IS_ERR_OR_NULL(node))
+		return PTR_ERR(node);
+
+	mutex_lock(&node->provider->lock);
+
+	dst = node_find(dst_id);
+	if (!dst)
+		dst = icc_node_create(dst_id);
+
+	new = krealloc(node->links,
+		       (node->num_links + 1) * sizeof(*node->links),
+		       GFP_KERNEL);
+	if (!new) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	node->links = new;
+	node->links[node->num_links++] = dst;
+
+out:
+	mutex_unlock(&node->provider->lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(icc_link_create);
+
+/**
+ * icc_add_node() - add an interconnect node to interconnect provider
+ * @node: pointer to the interconnect node
+ * @provider: pointer to the interconnect provider
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_node_add(struct icc_node *node, struct icc_provider *provider)
+{
+	if (WARN_ON(!node))
+		return -EINVAL;
+
+	if (WARN_ON(!provider))
+		return -EINVAL;
+
+	node->provider = provider;
+
+	mutex_lock(&provider->lock);
+	list_add_tail(&node->node_list, &provider->nodes);
+	mutex_unlock(&provider->lock);
+
+	return 0;
+}
+
+/**
+ * icc_add_provider() - add a new interconnect provider
+ * @icc_provider: the interconnect provider that will be added into topology
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_add_provider(struct icc_provider *provider)
+{
+	if (WARN_ON(!provider))
+		return -EINVAL;
+
+	if (WARN_ON(!provider->set))
+		return -EINVAL;
+
+	mutex_init(&provider->lock);
+	INIT_LIST_HEAD(&provider->nodes);
+
+	mutex_lock(&icc_provider_list_mutex);
+	list_add(&provider->provider_list, &icc_provider_list);
+	mutex_unlock(&icc_provider_list_mutex);
+
+	dev_dbg(provider->dev, "interconnect provider added to topology\n");
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(icc_add_provider);
+
+/**
+ * icc_del_provider() - delete previously added interconnect provider
+ * @icc_provider: the interconnect provider that will be removed from topology
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_del_provider(struct icc_provider *provider)
+{
+	mutex_lock(&provider->lock);
+	if (provider->users) {
+		pr_warn("interconnect provider still has %d users\n",
+			provider->users);
+	}
+	mutex_unlock(&provider->lock);
+
+	mutex_lock(&icc_provider_list_mutex);
+	list_del(&provider->provider_list);
+	mutex_unlock(&icc_provider_list_mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(icc_del_provider);
+
+MODULE_AUTHOR("Georgi Djakov <[e-mail]");
+MODULE_DESCRIPTION("Interconnect Driver Core");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/interconnect-provider.h b/include/linux/interconnect-provider.h
new file mode 100644
index 000000000000..779b5b5b1306
--- /dev/null
+++ b/include/linux/interconnect-provider.h
@@ -0,0 +1,109 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2018, Linaro Ltd.
+ * Author: Georgi Djakov <[e-mail]>
+ */
+
+#ifndef _LINUX_INTERCONNECT_PROVIDER_H
+#define _LINUX_INTERCONNECT_PROVIDER_H
+
+#include <linux/interconnect.h>
+
+struct icc_node;
+
+/**
+ * struct icc_provider - interconnect provider (controller) entity that might
+ * provide multiple interconnect controls
+ *
+ * @provider_list: list of the registered interconnect providers
+ * @nodes: internal list of the interconnect provider nodes
+ * @set: pointer to device specific set operation function
+ * @dev: the device this interconnect provider belongs to
+ * @lock: lock to provide consistency during aggregation/update of constraints
+ * @users: count of active users
+ * @data: pointer to private data
+ */
+struct icc_provider {
+	struct list_head	provider_list;
+	struct list_head	nodes;
+	int (*set)(struct icc_node *src, struct icc_node *dst,
+		   u32 avg_bw, u32 peak_bw);
+	struct device		*dev;
+	struct mutex		lock;
+	int			users;
+	void			*data;
+};
+
+/**
+ * struct icc_node - entity that is part of the interconnect topology
+ *
+ * @id: platform specific node id
+ * @name: node name used in debugfs
+ * @links: a list of targets where we can go next when traversing
+ * @num_links: number of links to other interconnect nodes
+ * @provider: points to the interconnect provider of this node
+ * @node_list: list of interconnect nodes associated with @provider
+ * @search_list: list used when walking the nodes graph
+ * @reverse: pointer to previous node when walking the nodes graph
+ * @is_traversed: flag that is used when walking the nodes graph
+ * @req_list: a list of QoS constraint requests associated with this node
+ * @avg_bw: aggregated value of average bandwidth
+ * @peak_bw: aggregated value of peak bandwidth
+ * @data: pointer to private data
+ */
+struct icc_node {
+	int			id;
+	const char              *name;
+	struct icc_node		**links;
+	size_t			num_links;
+
+	struct icc_provider	*provider;
+	struct list_head	node_list;
+	struct list_head	orphan_list;
+	struct list_head	search_list;
+	struct icc_node		*reverse;
+	bool			is_traversed;
+	struct hlist_head	req_list;
+	u32			avg_bw;
+	u32			peak_bw;
+	void			*data;
+};
+
+#if IS_ENABLED(CONFIG_INTERCONNECT)
+
+struct icc_node *icc_node_create(int id);
+int icc_node_add(struct icc_node *node, struct icc_provider *provider);
+int icc_link_create(struct icc_node *node, const int dst_id);
+int icc_add_provider(struct icc_provider *provider);
+int icc_del_provider(struct icc_provider *provider);
+
+#else
+
+static inline struct icc_node *icc_node_create(int id)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
+int icc_node_add(struct icc_node *node, struct icc_provider *provider)
+{
+	return -ENOTSUPP;
+}
+
+static inline int icc_link_create(struct icc_node *node, const int dst_id)
+{
+	return -ENOTSUPP;
+}
+
+static inline int icc_add_provider(struct icc_provider *provider)
+{
+	return -ENOTSUPP;
+}
+
+static inline int icc_del_provider(struct icc_provider *provider)
+{
+	return -ENOTSUPP;
+}
+
+#endif /* CONFIG_INTERCONNECT */
+
+#endif /* _LINUX_INTERCONNECT_PROVIDER_H */
diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
new file mode 100644
index 000000000000..5a7cf72b76a5
--- /dev/null
+++ b/include/linux/interconnect.h
@@ -0,0 +1,40 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2018, Linaro Ltd.
+ * Author: Georgi Djakov <[e-mail]>
+ */
+
+#ifndef _LINUX_INTERCONNECT_H
+#define _LINUX_INTERCONNECT_H
+
+#include <linux/types.h>
+#include <linux/mutex.h>
+
+struct icc_path;
+struct device;
+
+#if IS_ENABLED(CONFIG_INTERCONNECT)
+
+struct icc_path *icc_get(const int src_id, const int dst_id);
+void icc_put(struct icc_path *path);
+int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw);
+
+#else
+
+static inline struct icc_path *icc_get(const int src_id, const int dst_id)
+{
+	return NULL;
+}
+
+static inline void icc_put(struct icc_path *path)
+{
+}
+
+static inline int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
+{
+	return 0;
+}
+
+#endif /* CONFIG_INTERCONNECT */
+
+#endif /* _LINUX_INTERCONNECT_H */