new file mode 100644
@@ -0,0 +1,252 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============================================
+General description of the remoteproc subsystem
+===============================================
+
+Authors:
+ - anish kumar <yesanishhere@gmail.com>
+
+.. Contents:
+
+ 1. Introduction
+ 2. Remoteproc framework responsibilities
+ 3. Remoteproc driver responsibilities
+ 4. Virtio and rpmsg
+
+1. Introduction
+======================
+
+Modern System on Chips (SoCs) typically integrate heterogeneous remote
+processor devices in asymmetric multiprocessing (AMP) configurations.
+These processors may run different operating systems, such as Linux and
+various real-time operating systems (RTOS).
+
+For example, the OMAP4 platform features dual Cortex-A9 cores, dual
+Cortex-M3 cores, and a C64x+ DSP. In a standard setup, the Cortex-A9
+cores execute Linux in a symmetric multiprocessing (SMP) configuration,
+while the M3 cores and DSP run independent instances of an RTOS.
+
+The remoteproc framework allows various platforms and architectures to
+manage remote processors, including operations such as powering on,
+loading firmware, and powering off. This framework abstracts hardware
+differences, promoting code reuse and minimizing duplication. It also
+supports rpmsg virtio devices for remote processors that utilize this
+communication method. Consequently, platform-specific remoteproc drivers
+need only implement a few low-level handlers, enabling seamless operation
+of all rpmsg drivers. (For more details about the virtio-based rpmsg
+bus and its drivers, refer to :doc:`Documentation/staging/rpmsg.rst`.)
+
+Additionally, the framework allows for the registration of various
+virtio devices. Firmware can publish the types of virtio devices it
+supports, facilitating their addition to the remoteproc framework. This
+flexibility enables the reuse of existing virtio drivers with remote
+processor backends at minimal development cost.
+
+The primary purpose of the remoteproc framework is to download firmware
+for remote processors and manage their lifecycle. The framework consists
+of several key components:
+
+- **Character Driver**: Provides userspace access to control the remote
+ processor.
+- **ELF Utility**: Offers functions for handling ELF files and managing
+ resources requested by the remote processor.
+- **Remoteproc Core**: Manages firmware downloads and recovery actions
+ in case of a remote processor crash.
+- **Coredump**: Provides facilities for coredumping and tracing from
+ the remote processor in the event of a crash.
+- **Userspace Interaction**: Uses sysfs and debugfs to manage the
+ lifecycle and status of the remote processor.
+- **Virtio Support**: Facilitates interaction with the virtio and
+ rpmsg bus.
+
+From here on, references to "framework" denote the remoteproc
+framework, and "driver" refers to the remoteproc driver that utilizes
+the framework for managing remote processors.
+
+2. Remoteproc framework Responsibilities
+========================================
+
+The framework begins by gathering information about the firmware file
+to be downloaded through the request_firmware function. It supports
+the ELF format and parses the firmware image to identify the physical
+addresses that need to be populated from the corresponding ELF sections.
+The framework also requires knowledge of the logical or I/O-mapped
+addresses in the application processor. Once this information is
+obtained from the driver, the framework transfers the data to the
+specified addresses and starts the remote, along with
+any devices physically or logically connected to it.
+
+Dependent devices, referred to as `subdevices` within the framework,
+are also managed post-registration by their respective drivers.
+Subdevices can register themselves using `rproc_(add/remove)_subdev`.
+Non-remoteproc drivers can use subdevices as a way to logically connect
+to remote and get lifecycle notifications of the remote.
+
+The framework oversees the lifecycle of the remote and
+provides the `rproc_report_crash` function, which the driver invokes
+upon receiving a crash notification from the remote. The
+notification method can differ based on the design of the remote
+processor and its communication with the application processor. For
+instance, if the remote is a DSP equipped with a watchdog,
+unresponsive behavior triggers the watchdog, generating an interrupt
+that routes to the application processor, allowing it to call
+`rproc_report_crash` in the driver's interrupt context.
+
+During crash handling, the framework performs the following actions:
+
+a. Sends a request to stop the remote and any connected or
+ dependent subdevices.
+b. Generates a coredump, dumping all `resources` requested by the
+ remote alongside relevant debugging information. Resources are
+ explained below.
+c. Reloads the firmware and restarts the remote.
+
+If the `RPROC_FEAT_ATTACH_ON_RECOVERY` flag is set, the detach and
+attach callbacks of the driver are invoked without reloading the
+firmware. This is useful when the remote requires no
+assistance for recovery, or when the application processor can restart
+independently. After recovery, the application processor can reattach
+to the remote.
+
+The remote can request resources from the framework, which
+allocates a ".resource_table" section. During the ELF parsing phase,
+the framework identifies this section and calls the appropriate
+handler to allocate the requested resources.
+
+Resource management within the framework can accommodate any type of
+`fw_resource_type`.
+
+.. code-block:: c
+
+ enum fw_resource_type {
+ RSC_CARVEOUT = 0,
+ RSC_DEVMEM = 1,
+ RSC_TRACE = 2,
+ RSC_VDEV = 3,
+ RSC_LAST = 4,
+ RSC_VENDOR_START = 128,
+ RSC_VENDOR_END = 512,
+ };
+
+ struct resource_table {
+ u32 ver;
+ u32 num;
+ u32 reserved[2];
+ u32 offset[];
+ } __packed;
+
+ struct fw_rsc_hdr {
+ u32 type;
+ u8 data[];
+ } __packed;
+
+For example, if the remote requests both `RSC_TRACE` and
+`RSC_CARVEOUT` for memory allocation, the ELF firmware can be structured
+as follows:
+
+.. code-block:: c
+
+ #define MAX_SHARED_RESOURCE 2
+ #define LOG_BUF_SIZE 1000
+ #define CARVEOUT_DUMP_PA 0x12345678
+ #define CARVEOUT_DUMP_SIZE 2000
+
+ struct shared_resource_table {
+ u32 ver;
+ u32 num;
+ u32 reserved[2];
+ u32 offset[MAX_SHARED_RESOURCE];
+ struct fw_rsc_trace log_trace;
+ struct fw_rsc_carveout dump_carveout;
+ };
+
+ volatile struct shared_resource_table table = {
+ .ver = 1,
+ .num = 2,
+ .reserved = {0, 0},
+ .offset = {
+ offsetof(struct resource_table, log_trace),
+ offsetof(struct resource_table, dump_carveout),
+ },
+ .log_trace = {
+ RSC_TRACE,
+ (u32)log_buf, LOG_BUF_SIZE, 0, "log_trace",
+ },
+ .dump_carveout = {
+ RSC_CARVEOUT,
+ (u32)FW_RSC_ADDR_ANY, CARVEOUT_PA, 0, "carveout_dump",
+ },
+ };
+
+The framework creates a sysfs file when it encounters the `RSC_TRACE`
+type to expose log information to userspace. Other resource types are
+handled accordingly. In the example above, `CARVEOUT_DUMP_SIZE` bytes
+of DMA memory will be allocated starting from `CARVEOUT_DUMP_PA`.
+
+
+3. Remoteproc driver responsibilities
+=====================================
+
+The driver must provide the following information to the core:
+
+a. Translate device addresses (physical addresses) found in the ELF
+ firmware to virtual addresses in Linux using the `da_to_va`
+ callback. This allows the framework to copy ELF firmware from the
+ filesystem to the addresses expected by the remote since
+ the framework cannot directly access those physical addresses.
+b. Prepare/unprepare the remote prior to firmware loading,
+ which may involve allocating carveout and reserved memory regions.
+c. Implement methods for starting and stopping the remote,
+ whether by setting registers or sending explicit interrupts,
+ depending on the hardware design.
+d. Provide attach and detach callbacks to start the remote
+ without loading the firmware. This is beneficial when the remote
+ processor is already loaded and running.
+e. Implement a load callback for firmware loading, typically using
+ the ELF loader provided by the framework; currently, only ELF
+ format is supported.
+f. Invoke the framework's crash handler API upon detecting a remote
+ crash.
+
+Drivers must fill the `rproc_ops` structure and call `rproc_alloc`
+to register themselves with the framework.
+
+.. code-block:: c
+
+ struct rproc_ops {
+ int (*prepare)(struct rproc *rproc);
+ int (*unprepare)(struct rproc *rproc);
+ int (*start)(struct rproc *rproc);
+ int (*stop)(struct rproc *rproc);
+ int (*attach)(struct rproc *rproc);
+ int (*detach)(struct rproc *rproc);
+ void * (*da_to_va)(struct rproc *rproc, u64 da, size_t len,
+ bool *is_iomem);
+ int (*parse_fw)(struct rproc *rproc, const struct firmware *fw);
+ int (*handle_rsc)(struct rproc *rproc, u32 rsc_type,
+ void *rsc, int offset, int avail);
+ int (*load)(struct rproc *rproc, const struct firmware *fw);
+ //snip
+ };
+
+
+4. Virtio and Remoteproc
+========================
+
+The firmware must provide remoteproc with information regarding the
+virtio devices it supports and their configurations: an `RSC_VDEV`
+resource entry should detail the virtio device ID (as defined in
+`virtio_ids.h`), virtio features, virtio config space, vrings
+information, etc.
+
+Upon registration of a new remote, the remoteproc framework
+searches for its resource table and registers the supported virtio
+devices. A firmware may support multiple virtio devices, of various
+types (a single remote can support multiple rpmsg virtio
+devices if required).
+
+Moreover, `RSC_VDEV` resource entries suffice for static allocation
+of virtio devices. Dynamic allocations will also be supported using
+the rpmsg bus, akin to the handling of dynamic allocations for rpmsg
+channels. For more information, refer to `rpmsg.txt`.
new file mode 100644
@@ -0,0 +1,27 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================================================================
+remoteproc - remote processor subsystem in Linux(TM) kernel
+========================================================================
+
+Authors:
+ - anish kumar <yesanishhere@gmail.com>
+
+ remote processor subsystem is a way to manage the lifecycle of
+ a subsytem that is external to the Linux. The remoteproc framework
+ allows different platforms/architectures to control (power on,
+ load firmware, power off) those remote processors while abstracting
+ the hardware differences, so the entire driver doesn't need to be
+ duplicated.
+
+.. toctree::
+ :maxdepth: 1
+
+ core
+ rproc-api
+ rproc-kernel-api
+
+Mailing List
+------------
+To post a message, send an email to
+linux-remoteproc@vger.kernel.org
new file mode 100644
@@ -0,0 +1,75 @@
+==================================
+The Linux Remoteproc userspace API
+==================================
+
+Introduction
+============
+
+A Remoteproc (rproc) is a subsystem for managing the lifecycle
+of a processor that is connected to Linux.
+
+At times, userspace may need to check the state of the remote processor to
+prevent other processes from using it. For instance, if the remote processor
+is a DSP used for playback, there may be situations where the DSP is
+undergoing recovery and cannot be used. In such cases, attempts to access the
+DSP for playback should be blocked. The rproc framework provides sysfs APIs
+to inform userspace of the processor's current status which should be utilised
+to achieve the same.
+
+Additionally, there are scenarios where userspace applications need to explicitly
+control the rproc. In these cases, rproc also offers the file descriptors.
+
+The simplest API
+================
+
+Below set of api's can be used to start and stop the rproc
+where 'X' refers to instance of associated remoteproc. There can be systems
+where there are more than one rprocs such as multiple DSP's
+connected to application processors running Linux.
+::
+ echo start > /sys/class/remoteproc/remoteprocX/state
+ echo stop > /sys/class/remoteproc/remoteprocX/state
+
+To know the state of rproc:
+
+.. code-block::
+
+ cat /sys/class/remoteproc/remoteprocX/state
+
+
+To dynamically replace firmware, execute the following commands:
+
+.. code-block::
+
+ echo stop > /sys/class/remoteproc/remoteprocX/state
+ echo -n <firmware_name> >
+ /sys/class/remoteproc/remoteprocX/firmware
+ echo start > /sys/class/remoteproc/remoteprocX/state
+
+To simulate a remote crash, execute:
+
+.. code-block::
+
+ echo 1 > /sys/kernel/debug/remoteproc/remoteprocX/crash
+
+To get the trace logs, execute
+
+.. code-block::
+
+ cat /sys/kernel/debug/remoteproc/remoteprocX/crashX
+
+where X will be 0 or 1 if there are 2 resources. Also, this
+file will only exist if resources are defined in ELF firmware
+file.
+
+The coredump feature can be disabled with the following command:
+
+.. code-block::
+
+ echo disabled > /sys/kernel/debug/remoteproc/remoteprocX/coredump
+
+Userspace can also control start/stop of rproc by using a
+remoteproc Character Device, it can open the open a file descriptor
+and write `start` to initiate it, and `stop` to terminate it.
+
+[FIXME -- better explanations]
new file mode 100644
@@ -0,0 +1,239 @@
+=====================================================
+The Linux Remoteproc subsystem Driver Core kernel API
+=====================================================
+
+anish kumar <yesanishhere@gmail.com>
+
+Introduction
+------------
+This document does not describe what a Remote processor subsystem
+(RPROC) Driver or Device is. It also does not describe the API
+which can be used by user space to communicate with a RPROC driver.
+If you want to know this then please read the following
+file: Documentation/remoteproc/rproc-api.rst .
+
+So what does this document describe? It describes the API that can be used by
+remote processor Drivers that want to use the remote processor Driver Core
+Framework. This framework provides all interfacing towards user space so that
+the same code does not have to be reproduced each time. This also means that
+a remote processor driver then only needs to provide the different routines
+(operations) that control the remote processor.
+
+The API
+-------
+Each remote processor driver that wants to use the remote processor Driver Core
+must #include <linux/remoteproc.h> (you would have to do this anyway when
+writing a rproc device driver). This include file contains following
+register routine::
+
+ int devm_rproc_add(struct device *dev, struct rproc *rproc)
+
+The devm_rproc_add routine registers a remote processor device.
+The parameter of this routine is a pointer to a rproc device structure.
+This routine returns zero on success and a negative errno code for failure.
+
+The rproc device structure looks like this::
+
+ struct rproc {
+ struct list_head node;
+ struct iommu_domain *domain;
+ const char *name;
+ const char *firmware;
+ void *priv;
+ struct rproc_ops *ops;
+ struct device dev;
+ atomic_t power;
+ unsigned int state;
+ enum rproc_dump_mechanism dump_conf;
+ struct mutex lock;
+ struct dentry *dbg_dir;
+ struct list_head traces;
+ int num_traces;
+ struct list_head carveouts;
+ struct list_head mappings;
+ u64 bootaddr;
+ struct list_head rvdevs;
+ struct list_head subdevs;
+ struct idr notifyids;
+ int index;
+ struct work_struct crash_handler;
+ unsigned int crash_cnt;
+ bool recovery_disabled;
+ int max_notifyid;
+ struct resource_table *table_ptr;
+ struct resource_table *clean_table;
+ struct resource_table *cached_table;
+ size_t table_sz;
+ bool has_iommu;
+ bool auto_boot;
+ bool sysfs_read_only;
+ struct list_head dump_segments;
+ int nb_vdev;
+ u8 elf_class;
+ u16 elf_machine;
+ struct cdev cdev;
+ bool cdev_put_on_release;
+ DECLARE_BITMAP(features, RPROC_MAX_FEATURES);
+ };
+
+It contains following fields:
+
+* node: list node of this rproc object
+* domain: iommu domain
+* name: human readable name of the rproc
+* firmware: name of firmware file to be loaded
+* priv: private data which belongs to the platform-specific rproc module
+* ops: platform-specific start/stop rproc handlers
+* dev: virtual device for refcounting and common remoteproc behavior
+* power: refcount of users who need this rproc powered up
+* state: state of the device
+* dump_conf: Currently selected coredump configuration
+* lock: lock which protects concurrent manipulations of the rproc
+* dbg_dir: debugfs directory of this rproc device
+* traces: list of trace buffers
+* num_traces: number of trace buffers
+* carveouts: list of physically contiguous memory allocations
+* mappings: list of iommu mappings we initiated, needed on shutdown
+* bootaddr: address of first instruction to boot rproc with (optional)
+* rvdevs: list of remote virtio devices
+* subdevs: list of subdevices, to following the running state
+* notifyids: idr for dynamically assigning rproc-wide unique notify ids
+* index: index of this rproc device
+* crash_handler: workqueue for handling a crash
+* crash_cnt: crash counter
+* recovery_disabled: flag that state if recovery was disabled
+* max_notifyid: largest allocated notify id.
+* table_ptr: pointer to the resource table in effect
+* clean_table: copy of the resource table without modifications. Used
+* when a remote processor is attached or detached from the core
+* cached_table: copy of the resource table
+* table_sz: size of @cached_table
+* has_iommu: flag to indicate if remote processor is behind an MMU
+* auto_boot: flag to indicate if remote processor should be auto-started
+* sysfs_read_only: flag to make remoteproc sysfs files read only
+* dump_segments: list of segments in the firmware
+* nb_vdev: number of vdev currently handled by rproc
+* elf_class: firmware ELF class
+* elf_machine: firmware ELF machine
+* cdev: character device of the rproc
+* cdev_put_on_release: flag to indicate if remoteproc should be shutdown on @char_dev release
+* features: indicate remoteproc features
+
+The list of rproc operations is defined as::
+
+ struct rproc_ops {
+ int (*prepare)(struct rproc *rproc);
+ int (*unprepare)(struct rproc *rproc);
+ int (*start)(struct rproc *rproc);
+ int (*stop)(struct rproc *rproc);
+ int (*attach)(struct rproc *rproc);
+ int (*detach)(struct rproc *rproc);
+ void (*kick)(struct rproc *rproc, int vqid);
+ void * (*da_to_va)(struct rproc *rproc, u64 da, size_t len, bool *is_iomem);
+ int (*parse_fw)(struct rproc *rproc, const struct firmware *fw);
+ int (*handle_rsc)(struct rproc *rproc, u32 rsc_type, void *rsc,
+ int offset, int avail);
+ struct resource_table *(*find_loaded_rsc_table)(
+ struct rproc *rproc, const struct firmware *fw);
+ struct resource_table *(*get_loaded_rsc_table)(
+ struct rproc *rproc, size_t *size);
+ int (*load)(struct rproc *rproc, const struct firmware *fw);
+ int (*sanity_check)(struct rproc *rproc, const struct firmware *fw);
+ u64 (*get_boot_addr)(struct rproc *rproc, const struct firmware *fw);
+ unsigned long (*panic)(struct rproc *rproc);
+ void (*coredump)(struct rproc *rproc);
+ };
+
+Most of the operations are optional. Currently in the implementation
+there are no mandatory operations, however from the practical standpoint
+minimum ops are:
+
+* start: this is a pointer to the routine that starts the remote processor
+ device.
+ The routine needs a pointer to the remote processor device structure as a
+ parameter. It returns zero on success or a negative errno code for failure.
+
+* stop: with this routine the remote processor device is being stopped.
+
+ The routine needs a pointer to the remote processor device structure as a
+ parameter. It returns zero on success or a negative errno code for failure.
+
+* da_to_va: this is the routine that needs to translate device address to
+ application processor virtual address that it can copy code to.
+
+ The routine needs a pointer to the remote processor device structure as a
+ parameter. It returns zero on success or a negative errno code for failure.
+
+ The routine provides the device address it finds in the ELF firmware and asks
+ the driver to convert that to virtual address.
+
+All other callbacks are optional in case of ELF provided firmware.
+
+* load: this is to load the firmware on to the remote device.
+
+ The routine needs firmware file that it needs to load on to the remote processor.
+ If the driver overrides this callback then default ELF loader will not get used.
+ Otherwise default framework provided loader gets used.
+
+ load = rproc_elf_load_segments;
+ parse_fw = rproc_elf_load_rsc_table;
+ find_loaded_rsc_table = rproc_elf_find_loaded_rsc_table;
+ sanity_check = rproc_elf_sanity_check;
+ get_boot_addr = rproc_elf_get_boot_addr;
+
+* parse_fw: this routing parses the provided firmware. In case of ELF format,
+ framework provided rproc_elf_load_rsc_table function can be used.
+
+* sanity_check: Check the format of the firmware.
+
+* coredump: If the driver prefers to manage coredumps independently, it can
+ implement its own coredump handling. However, the framework offers a default
+ implementation for the ELF format by assigning this callback to
+ rproc_coredump, unless the driver has overridden it.
+
+* get_boot_addr: In case the bootaddr defined in ELF firmware is different, driver
+ can use this callback to set a different boot address for remote processor to
+ starts its reset vector from.
+
+* find_loaded_rsc_table: this routine gets the loaded resource table from the firmware.
+
+ resource table should have a section named (.resource_table) for the framework
+ to understand and interpret its content. Resource table is a way for remote
+ processor to ask for resources such as memory for dumping and logging. Look
+ at core documentation to know how to create the ELF section for the same.
+
+* get_loaded_rsc_table: Driver can customize passing the resource table by overriding
+ this callback. Framework doesn't provide any default implementation for the same.
+
+
+The rproc_report_crash function allows you to report a crash when crash is
+detected by the driver.
+
+::
+
+ void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type);
+
+To add a subdev corresponding driver can call::
+
+ void rproc_add_subdev(struct rproc *rproc, struct rproc_subdev *subdev);
+
+To remove a subdev, driver can call.
+
+::
+
+ void rproc_remove_subdev(struct rproc *rproc, struct rproc_subdev *subdev);
+
+To work with ELF coredump below function can be called::
+
+ void rproc_coredump_cleanup(struct rproc *rproc);
+ void rproc_coredump(struct rproc *rproc);
+ void rproc_coredump_using_sections(struct rproc *rproc);
+ int rproc_coredump_add_segment(struct rproc *rproc, dma_addr_t da, size_t size);
+ int rproc_coredump_add_custom_segment(struct rproc *rproc,
+ dma_addr_t da, size_t size,
+ void (*dumpfn)(struct rproc *rproc,
+ struct rproc_dump_segment *segment,
+ void *dest, size_t offset,
+ size_t size),
+
+Remember that coredump functions provided by the framework only works with ELF format.
@@ -15907,6 +15907,7 @@ S: Maintained
T: git git://git.kernel.org/pub/scm/linux/kernel/git/andersson/remoteproc.git rproc-next
F: Documentation/ABI/testing/sysfs-class-remoteproc
F: Documentation/devicetree/bindings/remoteproc/
+F: Documentation/remoteproc/
F: drivers/remoteproc/
F: include/linux/remoteproc.h
F: include/linux/remoteproc/
1. Add documentation for remoteproc core 2. Add userspace api documentation. 3. Add kernel driver api documentation. Signed-off-by: anish kumar <yesanishhere@gmail.com> --- | Reported-by: kernel test robot <lkp@intel.com> | Closes: https://lore.kernel.org/oe-kbuild-all/202410161444.jOKMsoGS-lkp@intel.com/ Documentation/remoteproc/core.rst | 252 ++++++++++++++++++ Documentation/remoteproc/index.rst | 27 ++ Documentation/remoteproc/rproc-api.rst | 75 ++++++ Documentation/remoteproc/rproc-kernel-api.rst | 239 +++++++++++++++++ MAINTAINERS | 1 + 5 files changed, 594 insertions(+) create mode 100644 Documentation/remoteproc/core.rst create mode 100644 Documentation/remoteproc/index.rst create mode 100644 Documentation/remoteproc/rproc-api.rst create mode 100644 Documentation/remoteproc/rproc-kernel-api.rst