[v10,1/7] interconnect: Add generic on-chip interconnect API

Commit Message

Georgi Djakov Nov. 27, 2018, 6:03 p.m. UTC

This patch introduces 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]>
Reviewed-by: Evan Green <[e-mail]>
---
 Documentation/interconnect/interconnect.rst |  94 ++++
 drivers/Kconfig                             |   2 +
 drivers/Makefile                            |   1 +
 drivers/interconnect/Kconfig                |  10 +
 drivers/interconnect/Makefile               |   5 +
 drivers/interconnect/core.c                 | 569 ++++++++++++++++++++
 include/linux/interconnect-provider.h       | 125 +++++
 include/linux/interconnect.h                |  51 ++
 8 files changed, 857 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

Joe Perches Nov. 27, 2018, 6:35 p.m. UTC | #1

On Tue, 2018-11-27 at 20:03 +0200, Georgi Djakov wrote:
> This patch introduces a new API to get requirements and configure the
> interconnect buses across the entire chipset to fit with the current
> demand.

trivial notes:

> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
[]
> +static int apply_constraints(struct icc_path *path)
> +{
> +	struct icc_node *next, *prev = NULL;
> +	int ret = -EINVAL;
> +	int i;
> +
> +	for (i = 0; i < path->num_nodes; i++, prev = next) {
> +		struct icc_provider *p;
> +
> +		next = path->reqs[i].node;
> +		/*
> +		 * Both endpoints should be valid master-slave pairs of the
> +		 * same interconnect provider that will be configured.
> +		 */
> +		if (!prev || next->provider != prev->provider)
> +			continue;
> +
> +		p = next->provider;
> +
> +		/* set the constraints */
> +		ret = p->set(prev, next);
> +		if (ret)
> +			goto out;
> +	}
> +out:
> +	return ret;
> +}

The use of ", prev = next" appears somewhat tricky code.
Perhaps move the assignment of prev to the bottom of the loop.
Perhaps the temporary p assignment isn't useful either.

> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
[]
> +	ret = apply_constraints(path);
> +	if (ret)
> +		pr_debug("interconnect: error applying constraints (%d)", ret);

Ideally all pr_<foo> formats should end in '\n'

> +static struct icc_node *icc_node_create_nolock(int id)
> +{
> +	struct icc_node *node;
> +
> +	/* check if node already exists */
> +	node = node_find(id);
> +	if (node)
> +		goto out;
> +
> +	node = kzalloc(sizeof(*node), GFP_KERNEL);
> +	if (!node) {
> +		node = ERR_PTR(-ENOMEM);
> +		goto out;

Generally, this code appears to overly rely on goto when
direct returns could be more readable.

> +	}
> +
> +	id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
> +	if (WARN(id < 0, "couldn't get idr")) {

This seems to unnecessarily hide the id < 0 test in a WARN

Why is this a WARN and not a simpler
	if (id < 0) {
		[ pr_err(...); or WARN(1, ...); ]

> +		kfree(node);
> +		node = ERR_PTR(id);
> +		goto out;
> +	}
> +
> +	node->id = id;
> +
> +out:
> +	return node;
> +}
[]
> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
[]
> +/* macros for converting to icc units */
> +#define bps_to_icc(x)	(1)
> +#define kBps_to_icc(x)	(x)
[]
> +#define MBps_to_icc(x)	(x * 1000)
> +#define GBps_to_icc(x)	(x * 1000 * 1000)
> +#define kbps_to_icc(x)	(x / 8 + ((x) % 8 ? 1 : 0))
> +#define Mbps_to_icc(x)	(x * 1000 / 8 )
> +#define Gbps_to_icc(x)	(x * 1000 * 1000 / 8)

The last 5 macros should parenthesize x

Georgi Djakov Nov. 28, 2018, 6:18 p.m. UTC | #2

Hi Joe,

On 11/27/18 20:35, Joe Perches wrote:
> On Tue, 2018-11-27 at 20:03 +0200, Georgi Djakov wrote:
>> This patch introduces a new API to get requirements and configure the
>> interconnect buses across the entire chipset to fit with the current
>> demand.
> 
> trivial notes:
> 
>> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> []
>> +static int apply_constraints(struct icc_path *path)
>> +{
>> +	struct icc_node *next, *prev = NULL;
>> +	int ret = -EINVAL;
>> +	int i;
>> +
>> +	for (i = 0; i < path->num_nodes; i++, prev = next) {
>> +		struct icc_provider *p;
>> +
>> +		next = path->reqs[i].node;
>> +		/*
>> +		 * Both endpoints should be valid master-slave pairs of the
>> +		 * same interconnect provider that will be configured.
>> +		 */
>> +		if (!prev || next->provider != prev->provider)
>> +			continue;
>> +
>> +		p = next->provider;
>> +
>> +		/* set the constraints */
>> +		ret = p->set(prev, next);
>> +		if (ret)
>> +			goto out;
>> +	}
>> +out:
>> +	return ret;
>> +}
> 
> The use of ", prev = next" appears somewhat tricky code.
> Perhaps move the assignment of prev to the bottom of the loop.
> Perhaps the temporary p assignment isn't useful either.
> 
>> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
>> +{
> []
>> +	ret = apply_constraints(path);
>> +	if (ret)
>> +		pr_debug("interconnect: error applying constraints (%d)", ret);
> 
> Ideally all pr_<foo> formats should end in '\n'
> 
>> +static struct icc_node *icc_node_create_nolock(int id)
>> +{
>> +	struct icc_node *node;
>> +
>> +	/* check if node already exists */
>> +	node = node_find(id);
>> +	if (node)
>> +		goto out;
>> +
>> +	node = kzalloc(sizeof(*node), GFP_KERNEL);
>> +	if (!node) {
>> +		node = ERR_PTR(-ENOMEM);
>> +		goto out;
> 
> Generally, this code appears to overly rely on goto when
> direct returns could be more readable.
> 
>> +	}
>> +
>> +	id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
>> +	if (WARN(id < 0, "couldn't get idr")) {
> 
> This seems to unnecessarily hide the id < 0 test in a WARN
> 
> Why is this a WARN and not a simpler
> 	if (id < 0) {
> 		[ pr_err(...); or WARN(1, ...); ]
> 
>> +		kfree(node);
>> +		node = ERR_PTR(id);
>> +		goto out;
>> +	}
>> +
>> +	node->id = id;
>> +
>> +out:
>> +	return node;
>> +}

Thank you for helping to improve the code. The above suggestions make it 
cleaner indeed.

> []
>> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
> []
>> +/* macros for converting to icc units */
>> +#define bps_to_icc(x)	(1)
>> +#define kBps_to_icc(x)	(x)
> []
>> +#define MBps_to_icc(x)	(x * 1000)
>> +#define GBps_to_icc(x)	(x * 1000 * 1000)
>> +#define kbps_to_icc(x)	(x / 8 + ((x) % 8 ? 1 : 0))
>> +#define Mbps_to_icc(x)	(x * 1000 / 8 )
>> +#define Gbps_to_icc(x)	(x * 1000 * 1000 / 8)
> 
> The last 5 macros should parenthesize x

Oops.. obviously i forgot to run checkpatch --strict. Will fix!

BR,
Georgi

Evan Green Dec. 1, 2018, 12:38 a.m. UTC | #3

On Tue, Nov 27, 2018 at 10:03 AM Georgi Djakov <[e-mail]> wrote:
>
> This patch introduces 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

Strange word ordering. Consider something like: "Then the providers
configure each node participating in the topology"

...Or a slightly different flavor: "Then the providers configure each
node along the path to support a bandwidth that satisfies all
bandwidth requests that cross through that node".

> constraints. The topology could be complicated and multi-tiered and is SoC
> specific.
>
> Signed-off-by: Georgi Djakov <[e-mail]>
> Reviewed-by: Evan Green <[e-mail]>

This already has my reviewed by, and I still stand by it, but I
couldn't help finding some nits anyway. Sorry :)

> ---
>  Documentation/interconnect/interconnect.rst |  94 ++++
>  drivers/Kconfig                             |   2 +
>  drivers/Makefile                            |   1 +
>  drivers/interconnect/Kconfig                |  10 +
>  drivers/interconnect/Makefile               |   5 +
>  drivers/interconnect/core.c                 | 569 ++++++++++++++++++++
>  include/linux/interconnect-provider.h       | 125 +++++
>  include/linux/interconnect.h                |  51 ++
>  8 files changed, 857 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..3ae8e5a58969
> --- /dev/null
> +++ b/drivers/interconnect/core.c
> @@ -0,0 +1,569 @@
> +// 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>
> +#include <linux/overflow.h>
> +
> +static DEFINE_IDR(icc_idr);
> +static LIST_HEAD(icc_providers);
> +static DEFINE_MUTEX(icc_lock);
> +
> +/**
> + * 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
> + * @dev: reference to the device that sets the constraints
> + * @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;
> +       struct device *dev;
> +       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[];
> +};
> +
> +static struct icc_node *node_find(const int id)
> +{
> +       return idr_find(&icc_idr, id);
> +}
> +
> +static struct icc_path *path_init(struct device *dev, struct icc_node *dst,
> +                                 ssize_t num_nodes)
> +{
> +       struct icc_node *node = dst;
> +       struct icc_path *path;
> +       int i;
> +
> +       path = kzalloc(struct_size(path, reqs, num_nodes), GFP_KERNEL);
> +       if (!path)
> +               return ERR_PTR(-ENOMEM);
> +
> +       path->num_nodes = num_nodes;
> +
> +       for (i = num_nodes - 1; i >= 0; i--) {
> +               node->provider->users++;
> +               hlist_add_head(&path->reqs[i].req_node, &node->req_list);
> +               path->reqs[i].node = node;
> +               path->reqs[i].dev = dev;
> +               /* reference to previous node was saved during path traversal */
> +               node = node->reverse;
> +       }
> +
> +       return path;
> +}
> +
> +static struct icc_path *path_find(struct device *dev, struct icc_node *src,
> +                                 struct icc_node *dst)
> +{
> +       struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
> +       struct icc_node *n, *node = NULL;
> +       struct list_head traverse_list;
> +       struct list_head edge_list;
> +       struct list_head visited_list;
> +       size_t i, depth = 1;
> +       bool found = false;
> +
> +       INIT_LIST_HEAD(&traverse_list);
> +       INIT_LIST_HEAD(&edge_list);
> +       INIT_LIST_HEAD(&visited_list);
> +
> +       list_add(&src->search_list, &traverse_list);
> +       src->reverse = NULL;
> +
> +       do {
> +               list_for_each_entry_safe(node, n, &traverse_list, search_list) {
> +                       if (node == dst) {
> +                               found = true;
> +                               list_splice_init(&edge_list, &visited_list);
> +                               list_splice_init(&traverse_list, &visited_list);
> +                               break;
> +                       }
> +                       for (i = 0; i < node->num_links; i++) {
> +                               struct icc_node *tmp = node->links[i];
> +
> +                               if (!tmp) {
> +                                       path = ERR_PTR(-ENOENT);
> +                                       goto out;
> +                               }
> +
> +                               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, &visited_list);
> +               list_splice_init(&edge_list, &traverse_list);
> +
> +               /* count the hops including the source */
> +               depth++;
> +
> +       } while (!list_empty(&traverse_list));
> +
> +out:
> +
> +       /* reset the traversed state */
> +       list_for_each_entry_reverse(n, &visited_list, search_list)
> +               n->is_traversed = false;
> +
> +       if (found)
> +               path = path_init(dev, dst, depth);
> +
> +       return path;
> +}
> +
> +/*
> + * We want the path to honor all bandwidth requests, so the average and peak
> + * bandwidth requirements from each consumer are aggregated at each node.
> + * The aggregation is platform specific, so each platform can customize it by
> + * implementing it's own aggregate() function.

Grammar police: remove the apostrophe in its.

> + */
> +
> +static int aggregate_requests(struct icc_node *node)
> +{
> +       struct icc_provider *p = node->provider;
> +       struct icc_req *r;
> +
> +       node->avg_bw = 0;
> +       node->peak_bw = 0;
> +
> +       hlist_for_each_entry(r, &node->req_list, req_node)
> +               p->aggregate(node, r->avg_bw, r->peak_bw,
> +                            &node->avg_bw, &node->peak_bw);
> +
> +       return 0;
> +}
> +
> +static int apply_constraints(struct icc_path *path)
> +{
> +       struct icc_node *next, *prev = NULL;
> +       int ret = -EINVAL;
> +       int i;
> +
> +       for (i = 0; i < path->num_nodes; i++, prev = next) {
> +               struct icc_provider *p;
> +
> +               next = path->reqs[i].node;
> +               /*
> +                * Both endpoints should be valid master-slave pairs of the
> +                * same interconnect provider that will be configured.
> +                */
> +               if (!prev || next->provider != prev->provider)
> +                       continue;

I wonder if we should explicitly ban paths where we bounce through an
odd number of nodes within one provider. Otherwise, set() won't be
called on all nodes in the path. Or, if we wanted to support those
kinds of topologies, you could call set with one of the nodes set to
NULL to represent either the ingress or egress bandwidth to this NoC.
This doesn't necessarily need to be addressed in this series, but is
something that other providers might bump into when implementing their
topologies.

> +
> +               p = next->provider;
> +
> +               /* set the constraints */
> +               ret = p->set(prev, next);
> +               if (ret)
> +                       goto out;
> +       }
> +out:
> +       return ret;
> +}
> +
...
> +
> +/**
> + * icc_link_destroy() - destroy a link between two nodes
> + * @src: pointer to source node
> + * @dst: pointer to destination node
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_link_destroy(struct icc_node *src, struct icc_node *dst)
> +{
> +       struct icc_node **new;
> +       size_t slot;
> +       int ret = 0;
> +
> +       if (IS_ERR_OR_NULL(src))
> +               return -EINVAL;
> +
> +       if (IS_ERR_OR_NULL(dst))
> +               return -EINVAL;
> +
> +       mutex_lock(&icc_lock);
> +
> +       for (slot = 0; slot < src->num_links; slot++)
> +               if (src->links[slot] == dst)
> +                       break;
> +
> +       if (WARN_ON(slot == src->num_links)) {
> +               ret = -ENXIO;
> +               goto out;
> +       }
> +
> +       src->links[slot] = src->links[--src->num_links];
> +
> +       new = krealloc(src->links,
> +                      (src->num_links) * sizeof(*src->links),

These parentheses aren't needed.

> +                      GFP_KERNEL);
> +       if (new)
> +               src->links = new;
> +
> +out:
> +       mutex_unlock(&icc_lock);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(icc_link_destroy);
> +
> +/**
> + * icc_node_add() - add interconnect node to interconnect provider
> + * @node: pointer to the interconnect node
> + * @provider: pointer to the interconnect provider
> + */
> +void icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +       mutex_lock(&icc_lock);
> +
> +       node->provider = provider;
> +       list_add_tail(&node->node_list, &provider->nodes);
> +
> +       mutex_unlock(&icc_lock);
> +}
> +EXPORT_SYMBOL_GPL(icc_node_add);
> +
> +/**
> + * icc_node_del() - delete interconnect node from interconnect provider
> + * @node: pointer to the interconnect node
> + */
> +void icc_node_del(struct icc_node *node)
> +{
> +       mutex_lock(&icc_lock);
> +
> +       list_del(&node->node_list);
> +
> +       mutex_unlock(&icc_lock);
> +}
> +EXPORT_SYMBOL_GPL(icc_node_del);
> +
> +/**
> + * icc_provider_add() - add a new interconnect provider
> + * @provider: the interconnect provider that will be added into topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_provider_add(struct icc_provider *provider)
> +{
> +       if (WARN_ON(!provider->set))
> +               return -EINVAL;
> +
> +       mutex_lock(&icc_lock);
> +
> +       INIT_LIST_HEAD(&provider->nodes);
> +       list_add_tail(&provider->provider_list, &icc_providers);
> +
> +       mutex_unlock(&icc_lock);
> +
> +       dev_dbg(provider->dev, "interconnect provider added to topology\n");
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_provider_add);
> +
> +/**
> + * icc_provider_del() - delete previously added interconnect provider
> + * @provider: the interconnect provider that will be removed from topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_provider_del(struct icc_provider *provider)
> +{
> +       mutex_lock(&icc_lock);
> +       if (provider->users) {
> +               pr_warn("interconnect provider still has %d users\n",
> +                       provider->users);
> +               mutex_unlock(&icc_lock);
> +               return -EBUSY;
> +       }
> +
> +       if (!list_empty(&provider->nodes)) {
> +               pr_warn("interconnect provider still has nodes\n");
> +               mutex_unlock(&icc_lock);
> +               return -EBUSY;
> +       }
> +
> +       list_del(&provider->provider_list);
> +       mutex_unlock(&icc_lock);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_provider_del);
> +
> +MODULE_AUTHOR("Georgi Djakov <[e-mail]");

This is missing the closing >

> +MODULE_DESCRIPTION("Interconnect Driver Core");
> +MODULE_LICENSE("GPL v2");
...
> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
> new file mode 100644
> index 000000000000..04b2966ded9f
> --- /dev/null
> +++ b/include/linux/interconnect.h
> @@ -0,0 +1,51 @@
> +/* 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/mutex.h>
> +#include <linux/types.h>
> +
> +/* macros for converting to icc units */
> +#define bps_to_icc(x)  (1)
> +#define kBps_to_icc(x) (x)
> +#define MBps_to_icc(x) (x * 1000)
> +#define GBps_to_icc(x) (x * 1000 * 1000)
> +#define kbps_to_icc(x) (x / 8 + ((x) % 8 ? 1 : 0))
> +#define Mbps_to_icc(x) (x * 1000 / 8 )

Remove extra space before )

> +#define Gbps_to_icc(x) (x * 1000 * 1000 / 8)
> +
> +struct icc_path;
> +struct device;
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_path *icc_get(struct device *dev, 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(struct device *dev, 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;

Should this really succeed?

> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* __LINUX_INTERCONNECT_H */

Georgi Djakov Dec. 5, 2018, 3:57 p.m. UTC | #4

Hi Evan,

On 12/1/18 02:38, Evan Green wrote:
> On Tue, Nov 27, 2018 at 10:03 AM Georgi Djakov <[e-mail]> wrote:
>>
>> This patch introduces 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
> 
> Strange word ordering. Consider something like: "Then the providers
> configure each node participating in the topology"
> 
> ...Or a slightly different flavor: "Then the providers configure each
> node along the path to support a bandwidth that satisfies all
> bandwidth requests that cross through that node".
> 

This sounds better!

>> constraints. The topology could be complicated and multi-tiered and is SoC
>> specific.
>>
>> Signed-off-by: Georgi Djakov <[e-mail]>
>> Reviewed-by: Evan Green <[e-mail]>
> 
> This already has my reviewed by, and I still stand by it, but I
> couldn't help finding some nits anyway. Sorry :)

Thanks for finding them!

>> ---
>>  Documentation/interconnect/interconnect.rst |  94 ++++
>>  drivers/Kconfig                             |   2 +
>>  drivers/Makefile                            |   1 +
>>  drivers/interconnect/Kconfig                |  10 +
>>  drivers/interconnect/Makefile               |   5 +
>>  drivers/interconnect/core.c                 | 569 ++++++++++++++++++++
>>  include/linux/interconnect-provider.h       | 125 +++++
>>  include/linux/interconnect.h                |  51 ++
>>  8 files changed, 857 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
>>
[..]
>> +/*
>> + * We want the path to honor all bandwidth requests, so the average and peak
>> + * bandwidth requirements from each consumer are aggregated at each node.
>> + * The aggregation is platform specific, so each platform can customize it by
>> + * implementing it's own aggregate() function.
> 
> Grammar police: remove the apostrophe in its.
> 

Oops.

>> + */
>> +
>> +static int aggregate_requests(struct icc_node *node)
>> +{
>> +       struct icc_provider *p = node->provider;
>> +       struct icc_req *r;
>> +
>> +       node->avg_bw = 0;
>> +       node->peak_bw = 0;
>> +
>> +       hlist_for_each_entry(r, &node->req_list, req_node)
>> +               p->aggregate(node, r->avg_bw, r->peak_bw,
>> +                            &node->avg_bw, &node->peak_bw);
>> +
>> +       return 0;
>> +}
>> +
>> +static int apply_constraints(struct icc_path *path)
>> +{
>> +       struct icc_node *next, *prev = NULL;
>> +       int ret = -EINVAL;
>> +       int i;
>> +
>> +       for (i = 0; i < path->num_nodes; i++, prev = next) {
>> +               struct icc_provider *p;
>> +
>> +               next = path->reqs[i].node;
>> +               /*
>> +                * Both endpoints should be valid master-slave pairs of the
>> +                * same interconnect provider that will be configured.
>> +                */
>> +               if (!prev || next->provider != prev->provider)
>> +                       continue;
> 
> I wonder if we should explicitly ban paths where we bounce through an
> odd number of nodes within one provider. Otherwise, set() won't be
> called on all nodes in the path. Or, if we wanted to support those
> kinds of topologies, you could call set with one of the nodes set to
> NULL to represent either the ingress or egress bandwidth to this NoC.
> This doesn't necessarily need to be addressed in this series, but is
> something that other providers might bump into when implementing their
> topologies.
> 

Yes, we can do something like this. But i prefer that we first add
support for more platforms and then according to the requirements we can
work out something.

[..]

>> +       new = krealloc(src->links,
>> +                      (src->num_links) * sizeof(*src->links),
> 
> These parentheses aren't needed.

Sure!

>> +                      GFP_KERNEL);
>> +       if (new)
>> +               src->links = new;
>> +

[..]

>> +
>> +MODULE_AUTHOR("Georgi Djakov <[e-mail]");
> 
> This is missing the closing >

Thanks!

>> +MODULE_DESCRIPTION("Interconnect Driver Core");
>> +MODULE_LICENSE("GPL v2");
> ...
>> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
>> new file mode 100644
>> index 000000000000..04b2966ded9f
>> --- /dev/null
>> +++ b/include/linux/interconnect.h
>> @@ -0,0 +1,51 @@
>> +/* 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/mutex.h>
>> +#include <linux/types.h>
>> +
>> +/* macros for converting to icc units */
>> +#define bps_to_icc(x)  (1)
>> +#define kBps_to_icc(x) (x)
>> +#define MBps_to_icc(x) (x * 1000)
>> +#define GBps_to_icc(x) (x * 1000 * 1000)
>> +#define kbps_to_icc(x) (x / 8 + ((x) % 8 ? 1 : 0))
>> +#define Mbps_to_icc(x) (x * 1000 / 8 )
> 
> Remove extra space before )

Done.

>> +#define Gbps_to_icc(x) (x * 1000 * 1000 / 8)
>> +
>> +struct icc_path;
>> +struct device;
>> +
>> +#if IS_ENABLED(CONFIG_INTERCONNECT)
>> +
>> +struct icc_path *icc_get(struct device *dev, 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(struct device *dev, 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;
> 
> Should this really succeed?

Yes, it should succeed if the framework is not enabled. The drivers
should handle the case of whether the framework is enabled or not when
icc_get() or of_icc_get() returns NULL. Based on that they should decide
if can continue without interconnect support or not.

BR,
Georgi

Rob Herring Dec. 5, 2018, 4:16 p.m. UTC | #5

On Tue, Nov 27, 2018 at 12:03 PM Georgi Djakov <[e-mail]> wrote:
>
> This patch introduces 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]>
> Reviewed-by: Evan Green <[e-mail]>

[...]

> +struct icc_path *icc_get(struct device *dev, 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);

icc_set() is very generic, but this function isn't easily extended to
other parameters than bandwidth. Perhaps icc_set_bandwidth() instead.
Then when you add some other setting, you just add a new function. Of
course, if you wind up with a bunch of different parameters, then
you'll probably need an atomic type interface where you test all the
settings together and then commit them separately in one call. But
from a DT perspective, I certainly hope there are not lots of new
settings folks want to add. :)

Rob

Georgi Djakov Dec. 7, 2018, 3:24 p.m. UTC | #6

Hi Rob,

On 12/5/18 18:16, Rob Herring wrote:
> On Tue, Nov 27, 2018 at 12:03 PM Georgi Djakov <[e-mail]> wrote:
>>
>> This patch introduces 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]>
>> Reviewed-by: Evan Green <[e-mail]>
> 
> [...]
> 
>> +struct icc_path *icc_get(struct device *dev, 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);
> 
> icc_set() is very generic, but this function isn't easily extended to
> other parameters than bandwidth. Perhaps icc_set_bandwidth() instead.
> Then when you add some other setting, you just add a new function. Of
> course, if you wind up with a bunch of different parameters, then
> you'll probably need an atomic type interface where you test all the
> settings together and then commit them separately in one call. But

Thanks for the comment. We have already started some discussion with the
Nvidia guys about supporting also latency and priority. We can do a
structure based approach and pass a struct with all the bandwidth /
latency / priority stuff to a function like icc_set_extended(); It's
very early for any conclusions yet and for now we support only
bandwidth. The function name still can be easy changed with a follow-up
patch until one is using it yet. Let me think again.

> from a DT perspective, I certainly hope there are not lots of new
> settings folks want to add. 
Regarding DT, all settings should go into the drivers for now and
later we can decide if something makes sense to be really in device-tree.

Thanks,
Georgi

Patch

diff --git a/Documentation/interconnect/interconnect.rst b/Documentation/interconnect/interconnect.rst
new file mode 100644
index 000000000000..b8107dcc4cd3
--- /dev/null
+++ b/Documentation/interconnect/interconnect.rst
@@ -0,0 +1,94 @@ 
+.. 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 an 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 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 an 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, P 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 connect 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 interconnect bus hardware. The interconnect provider drivers should
+be registered with the interconnect provider core.
+
+.. 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.
+
+.. kernel-doc:: include/linux/interconnect.h
diff --git a/drivers/Kconfig b/drivers/Kconfig
index ab4d43923c4d..ec510981554a 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 578f469f72fb..06f68339e2a7 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -186,3 +186,4 @@  obj-$(CONFIG_MULTIPLEXER)	+= mux/
 obj-$(CONFIG_UNISYS_VISORBUS)	+= visorbus/
 obj-$(CONFIG_SIOX)		+= siox/
 obj-$(CONFIG_GNSS)		+= gnss/
+obj-$(CONFIG_INTERCONNECT)	+= interconnect/
diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig
new file mode 100644
index 000000000000..a261c7d41deb
--- /dev/null
+++ b/drivers/interconnect/Kconfig
@@ -0,0 +1,10 @@ 
+menuconfig INTERCONNECT
+	tristate "On-Chip Interconnect management support"
+	help
+	  Support for management of the on-chip interconnects.
+
+	  This framework is designed to provide a generic interface for
+	  managing the interconnects in a SoC.
+
+	  If unsure, say no.
+
diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
new file mode 100644
index 000000000000..7a01f33b5593
--- /dev/null
+++ b/drivers/interconnect/Makefile
@@ -0,0 +1,5 @@ 
+# SPDX-License-Identifier: GPL-2.0
+
+icc-core-objs				:= core.o
+
+obj-$(CONFIG_INTERCONNECT)		+= icc-core.o
diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
new file mode 100644
index 000000000000..3ae8e5a58969
--- /dev/null
+++ b/drivers/interconnect/core.c
@@ -0,0 +1,569 @@ 
+// 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>
+#include <linux/overflow.h>
+
+static DEFINE_IDR(icc_idr);
+static LIST_HEAD(icc_providers);
+static DEFINE_MUTEX(icc_lock);
+
+/**
+ * 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
+ * @dev: reference to the device that sets the constraints
+ * @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;
+	struct device *dev;
+	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[];
+};
+
+static struct icc_node *node_find(const int id)
+{
+	return idr_find(&icc_idr, id);
+}
+
+static struct icc_path *path_init(struct device *dev, struct icc_node *dst,
+				  ssize_t num_nodes)
+{
+	struct icc_node *node = dst;
+	struct icc_path *path;
+	int i;
+
+	path = kzalloc(struct_size(path, reqs, num_nodes), GFP_KERNEL);
+	if (!path)
+		return ERR_PTR(-ENOMEM);
+
+	path->num_nodes = num_nodes;
+
+	for (i = num_nodes - 1; i >= 0; i--) {
+		node->provider->users++;
+		hlist_add_head(&path->reqs[i].req_node, &node->req_list);
+		path->reqs[i].node = node;
+		path->reqs[i].dev = dev;
+		/* reference to previous node was saved during path traversal */
+		node = node->reverse;
+	}
+
+	return path;
+}
+
+static struct icc_path *path_find(struct device *dev, struct icc_node *src,
+				  struct icc_node *dst)
+{
+	struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
+	struct icc_node *n, *node = NULL;
+	struct list_head traverse_list;
+	struct list_head edge_list;
+	struct list_head visited_list;
+	size_t i, depth = 1;
+	bool found = false;
+
+	INIT_LIST_HEAD(&traverse_list);
+	INIT_LIST_HEAD(&edge_list);
+	INIT_LIST_HEAD(&visited_list);
+
+	list_add(&src->search_list, &traverse_list);
+	src->reverse = NULL;
+
+	do {
+		list_for_each_entry_safe(node, n, &traverse_list, search_list) {
+			if (node == dst) {
+				found = true;
+				list_splice_init(&edge_list, &visited_list);
+				list_splice_init(&traverse_list, &visited_list);
+				break;
+			}
+			for (i = 0; i < node->num_links; i++) {
+				struct icc_node *tmp = node->links[i];
+
+				if (!tmp) {
+					path = ERR_PTR(-ENOENT);
+					goto out;
+				}
+
+				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, &visited_list);
+		list_splice_init(&edge_list, &traverse_list);
+
+		/* count the hops including the source */
+		depth++;
+
+	} while (!list_empty(&traverse_list));
+
+out:
+
+	/* reset the traversed state */
+	list_for_each_entry_reverse(n, &visited_list, search_list)
+		n->is_traversed = false;
+
+	if (found)
+		path = path_init(dev, dst, depth);
+
+	return path;
+}
+
+/*
+ * We want the path to honor all bandwidth requests, so the average and peak
+ * bandwidth requirements from each consumer are aggregated at each node.
+ * The aggregation is platform specific, so each platform can customize it by
+ * implementing it's own aggregate() function.
+ */
+
+static int aggregate_requests(struct icc_node *node)
+{
+	struct icc_provider *p = node->provider;
+	struct icc_req *r;
+
+	node->avg_bw = 0;
+	node->peak_bw = 0;
+
+	hlist_for_each_entry(r, &node->req_list, req_node)
+		p->aggregate(node, r->avg_bw, r->peak_bw,
+			     &node->avg_bw, &node->peak_bw);
+
+	return 0;
+}
+
+static int apply_constraints(struct icc_path *path)
+{
+	struct icc_node *next, *prev = NULL;
+	int ret = -EINVAL;
+	int i;
+
+	for (i = 0; i < path->num_nodes; i++, prev = next) {
+		struct icc_provider *p;
+
+		next = path->reqs[i].node;
+		/*
+		 * Both endpoints should be valid master-slave pairs of the
+		 * same interconnect provider that will be configured.
+		 */
+		if (!prev || next->provider != prev->provider)
+			continue;
+
+		p = next->provider;
+
+		/* set the constraints */
+		ret = p->set(prev, next);
+		if (ret)
+			goto out;
+	}
+out:
+	return ret;
+}
+
+/**
+ * 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 kilobytes per second
+ * @peak_bw: peak bandwidth in kilobytes per second
+ *
+ * This function is used by an interconnect consumer to express its own needs
+ * in terms of bandwidth for a previously requested path between two endpoints.
+ * The requests are aggregated and each node is updated accordingly. The entire
+ * path is locked by a mutex to ensure that the set() is completed.
+ * The @path can be NULL when the "interconnects" DT properties is missing,
+ * which will mean that no constraints will be set.
+ *
+ * Returns 0 on success, or an appropriate 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;
+
+	mutex_lock(&icc_lock);
+
+	for (i = 0; i < path->num_nodes; i++) {
+		node = path->reqs[i].node;
+
+		/* 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 */
+		aggregate_requests(node);
+	}
+
+	ret = apply_constraints(path);
+	if (ret)
+		pr_debug("interconnect: error applying constraints (%d)", ret);
+
+	mutex_unlock(&icc_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(icc_set);
+
+/**
+ * icc_get() - return a handle for path between two endpoints
+ * @dev: the device requesting the path
+ * @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 they are not needed anymore.
+ * If the interconnect API is disabled, NULL is returned and the consumer
+ * drivers will still build. Drivers are free to handle this specifically,
+ * but they don't have to.
+ *
+ * Return: icc_path pointer on success, ERR_PTR() on error or NULL if the
+ * interconnect API is disabled.
+ */
+struct icc_path *icc_get(struct device *dev, const int src_id, const int dst_id)
+{
+	struct icc_node *src, *dst;
+	struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
+
+	mutex_lock(&icc_lock);
+
+	src = node_find(src_id);
+	if (!src)
+		goto out;
+
+	dst = node_find(dst_id);
+	if (!dst)
+		goto out;
+
+	path = path_find(dev, src, dst);
+	if (IS_ERR(path))
+		dev_err(dev, "%s: invalid path=%ld\n", __func__, PTR_ERR(path));
+
+out:
+	mutex_unlock(&icc_lock);
+	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(IS_ERR(path)))
+		return;
+
+	ret = icc_set(path, 0, 0);
+	if (ret)
+		pr_err("%s: error (%d)\n", __func__, ret);
+
+	mutex_lock(&icc_lock);
+	for (i = 0; i < path->num_nodes; i++) {
+		node = path->reqs[i].node;
+		hlist_del(&path->reqs[i].req_node);
+		if (!WARN_ON(!node->provider->users))
+			node->provider->users--;
+	}
+	mutex_unlock(&icc_lock);
+
+	kfree(path);
+}
+EXPORT_SYMBOL_GPL(icc_put);
+
+static struct icc_node *icc_node_create_nolock(int id)
+{
+	struct icc_node *node;
+
+	/* check if node already exists */
+	node = node_find(id);
+	if (node)
+		goto out;
+
+	node = kzalloc(sizeof(*node), GFP_KERNEL);
+	if (!node) {
+		node = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+
+	id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
+	if (WARN(id < 0, "couldn't get idr")) {
+		kfree(node);
+		node = ERR_PTR(id);
+		goto out;
+	}
+
+	node->id = id;
+
+out:
+	return node;
+}
+
+/**
+ * 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;
+
+	mutex_lock(&icc_lock);
+
+	node = icc_node_create_nolock(id);
+
+	mutex_unlock(&icc_lock);
+
+	return node;
+}
+EXPORT_SYMBOL_GPL(icc_node_create);
+
+/**
+ * icc_node_destroy() - destroy a node
+ * @id: node id
+ */
+void icc_node_destroy(int id)
+{
+	struct icc_node *node;
+
+	mutex_lock(&icc_lock);
+
+	node = node_find(id);
+	if (node) {
+		idr_remove(&icc_idr, node->id);
+		WARN_ON(!hlist_empty(&node->req_list));
+	}
+
+	mutex_unlock(&icc_lock);
+
+	kfree(node);
+}
+EXPORT_SYMBOL_GPL(icc_node_destroy);
+
+/**
+ * icc_link_create() - create a link between two nodes
+ * @node: source node id
+ * @dst_id: destination node id
+ *
+ * Create a link between two nodes. The nodes might belong to different
+ * interconnect providers and the @dst_id node might not exist (if the
+ * provider driver has not probed yet). So just create the @dst_id node
+ * and when the actual provider driver is probed, the rest of the node
+ * data is filled.
+ *
+ * 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 (!node->provider)
+		return -EINVAL;
+
+	mutex_lock(&icc_lock);
+
+	dst = node_find(dst_id);
+	if (!dst) {
+		dst = icc_node_create_nolock(dst_id);
+
+		if (IS_ERR(dst)) {
+			ret = PTR_ERR(dst);
+			goto out;
+		}
+	}
+
+	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(&icc_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(icc_link_create);
+
+/**
+ * icc_link_destroy() - destroy a link between two nodes
+ * @src: pointer to source node
+ * @dst: pointer to destination node
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_link_destroy(struct icc_node *src, struct icc_node *dst)
+{
+	struct icc_node **new;
+	size_t slot;
+	int ret = 0;
+
+	if (IS_ERR_OR_NULL(src))
+		return -EINVAL;
+
+	if (IS_ERR_OR_NULL(dst))
+		return -EINVAL;
+
+	mutex_lock(&icc_lock);
+
+	for (slot = 0; slot < src->num_links; slot++)
+		if (src->links[slot] == dst)
+			break;
+
+	if (WARN_ON(slot == src->num_links)) {
+		ret = -ENXIO;
+		goto out;
+	}
+
+	src->links[slot] = src->links[--src->num_links];
+
+	new = krealloc(src->links,
+		       (src->num_links) * sizeof(*src->links),
+		       GFP_KERNEL);
+	if (new)
+		src->links = new;
+
+out:
+	mutex_unlock(&icc_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(icc_link_destroy);
+
+/**
+ * icc_node_add() - add interconnect node to interconnect provider
+ * @node: pointer to the interconnect node
+ * @provider: pointer to the interconnect provider
+ */
+void icc_node_add(struct icc_node *node, struct icc_provider *provider)
+{
+	mutex_lock(&icc_lock);
+
+	node->provider = provider;
+	list_add_tail(&node->node_list, &provider->nodes);
+
+	mutex_unlock(&icc_lock);
+}
+EXPORT_SYMBOL_GPL(icc_node_add);
+
+/**
+ * icc_node_del() - delete interconnect node from interconnect provider
+ * @node: pointer to the interconnect node
+ */
+void icc_node_del(struct icc_node *node)
+{
+	mutex_lock(&icc_lock);
+
+	list_del(&node->node_list);
+
+	mutex_unlock(&icc_lock);
+}
+EXPORT_SYMBOL_GPL(icc_node_del);
+
+/**
+ * icc_provider_add() - add a new interconnect provider
+ * @provider: the interconnect provider that will be added into topology
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_provider_add(struct icc_provider *provider)
+{
+	if (WARN_ON(!provider->set))
+		return -EINVAL;
+
+	mutex_lock(&icc_lock);
+
+	INIT_LIST_HEAD(&provider->nodes);
+	list_add_tail(&provider->provider_list, &icc_providers);
+
+	mutex_unlock(&icc_lock);
+
+	dev_dbg(provider->dev, "interconnect provider added to topology\n");
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(icc_provider_add);
+
+/**
+ * icc_provider_del() - delete previously added interconnect provider
+ * @provider: the interconnect provider that will be removed from topology
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_provider_del(struct icc_provider *provider)
+{
+	mutex_lock(&icc_lock);
+	if (provider->users) {
+		pr_warn("interconnect provider still has %d users\n",
+			provider->users);
+		mutex_unlock(&icc_lock);
+		return -EBUSY;
+	}
+
+	if (!list_empty(&provider->nodes)) {
+		pr_warn("interconnect provider still has nodes\n");
+		mutex_unlock(&icc_lock);
+		return -EBUSY;
+	}
+
+	list_del(&provider->provider_list);
+	mutex_unlock(&icc_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(icc_provider_del);
+
+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..78208a754181
--- /dev/null
+++ b/include/linux/interconnect-provider.h
@@ -0,0 +1,125 @@ 
+/* 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>
+
+#define icc_units_to_bps(bw)  ((bw) * 1000ULL)
+
+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
+ * @aggregate: pointer to device specific aggregate operation function
+ * @dev: the device this interconnect provider belongs to
+ * @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);
+	int (*aggregate)(struct icc_node *node, u32 avg_bw, u32 peak_bw,
+			 u32 *agg_avg, u32 *agg_peak);
+	struct device		*dev;
+	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 pointing to 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: the list entry in the parent provider's "nodes" list
+ * @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 requests from all consumers
+ * @peak_bw: aggregated value of 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	search_list;
+	struct icc_node		*reverse;
+	u8			is_traversed:1;
+	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);
+void icc_node_destroy(int id);
+int icc_link_create(struct icc_node *node, const int dst_id);
+int icc_link_destroy(struct icc_node *src, struct icc_node *dst);
+void icc_node_add(struct icc_node *node, struct icc_provider *provider);
+void icc_node_del(struct icc_node *node);
+int icc_provider_add(struct icc_provider *provider);
+int icc_provider_del(struct icc_provider *provider);
+
+#else
+
+static inline struct icc_node *icc_node_create(int id)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
+void icc_node_destroy(int id)
+{
+}
+
+static inline int icc_link_create(struct icc_node *node, const int dst_id)
+{
+	return -ENOTSUPP;
+}
+
+int icc_link_destroy(struct icc_node *src, struct icc_node *dst)
+{
+	return -ENOTSUPP;
+}
+
+void icc_node_add(struct icc_node *node, struct icc_provider *provider)
+{
+}
+
+void icc_node_del(struct icc_node *node)
+{
+}
+
+static inline int icc_provider_add(struct icc_provider *provider)
+{
+	return -ENOTSUPP;
+}
+
+static inline int icc_provider_del(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..04b2966ded9f
--- /dev/null
+++ b/include/linux/interconnect.h
@@ -0,0 +1,51 @@ 
+/* 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/mutex.h>
+#include <linux/types.h>
+
+/* macros for converting to icc units */
+#define bps_to_icc(x)	(1)
+#define kBps_to_icc(x)	(x)
+#define MBps_to_icc(x)	(x * 1000)
+#define GBps_to_icc(x)	(x * 1000 * 1000)
+#define kbps_to_icc(x)	(x / 8 + ((x) % 8 ? 1 : 0))
+#define Mbps_to_icc(x)	(x * 1000 / 8 )
+#define Gbps_to_icc(x)	(x * 1000 * 1000 / 8)
+
+struct icc_path;
+struct device;
+
+#if IS_ENABLED(CONFIG_INTERCONNECT)
+
+struct icc_path *icc_get(struct device *dev, 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(struct device *dev, 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 */