Message-Id: <20241026212259.31950-1-yesanishhere@gmail.com>
Date: Sat, 26 Oct 2024 14:22:59 -0700
From: anish kumar <yesanishhere@...il.com>
To: andersson@...nel.org,
	mathieu.poirier@...aro.orgi,
	corbet@....net
Cc: linux-doc@...r.kernel.org,
	linux-remoteproc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	anish kumar <yesanishhere@...il.com>,
	kernel test robot <lkp@...el.com>
Subject: [PATCH V5] remoteproc: Documentation: update with details

Added details as below:
1. added sysfs information
2. verbose details about remoteproc driver/framework
   responsibilites.
3. example for resource request

Signed-off-by: anish kumar <yesanishhere@...il.com>
---
V5:
based on comment from mathieu poirier, remove all files
and combined that in the original file and as he adviced
nothing with respect to old documentation was changed.

V4:
Fixed compilation errors and moved documentation to
driver-api directory.

V3:
Seperated out the patches further to make the intention
clear for each patch.

V2:
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202410161444.jOKMsoGS-lkp@intel.com/

 Documentation/staging/remoteproc.rst | 483 +++++++++++++++++++++++++++
 1 file changed, 483 insertions(+)

diff --git a/Documentation/staging/remoteproc.rst b/Documentation/staging/remoteproc.rst
index 348ee7e508ac..1c15f4d1b9eb 100644
--- a/Documentation/staging/remoteproc.rst
+++ b/Documentation/staging/remoteproc.rst
@@ -29,6 +29,68 @@ remoteproc will add those devices. This makes it possible to reuse the
 existing virtio drivers with remote processor backends at a 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.
+
+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.
+
 User API
 ========
 
@@ -107,6 +169,239 @@ Typical usage
 API for implementors
 ====================
 
+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.
+
+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 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
+   };
+
 ::
 
   struct rproc *rproc_alloc(struct device *dev, const char *name,
@@ -190,6 +485,35 @@ platform specific rproc implementation. This should not be called from a
 non-remoteproc driver. This function can be called from atomic/interrupt
 context.
 
+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.
+
 Implementation callbacks
 ========================
 
@@ -228,6 +552,123 @@ the exact virtqueue index to look in is optional: it is easy (and not
 too expensive) to go through the existing virtqueues and look for new buffers
 in the used rings.
 
+Userspace control methods
+==========================
+
+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.
+
+Below set of commands 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.
+
+.. code-block:: c
+
+   echo start > /sys/class/remoteproc/remoteprocX/state
+   echo stop > /sys/class/remoteproc/remoteprocX/state
+
+To know the state of rproc:
+
+.. code-block:: c
+
+   cat /sys/class/remoteproc/remoteprocX/state
+
+
+To dynamically replace firmware, execute the following commands:
+
+.. code-block:: c
+
+   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:: c
+
+   echo 1 > /sys/kernel/debug/remoteproc/remoteprocX/crash
+
+To get the trace logs, execute
+
+.. code-block:: c
+
+   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:: c
+
+   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.
+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.
+
+.. code-block:: c
+
+   echo start > /sys/class/remoteproc/remoteprocX/state
+   echo stop > /sys/class/remoteproc/remoteprocX/state
+
+To know the state of rproc:
+
+.. code-block:: c
+
+   cat /sys/class/remoteproc/remoteprocX/state
+
+
+To dynamically replace firmware, execute the following commands:
+
+.. code-block:: c
+
+   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:: c
+
+   echo 1 > /sys/kernel/debug/remoteproc/remoteprocX/crash
+
+To get the trace logs, execute
+
+.. code-block:: c
+
+   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:: c
+
+   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.
+
 Binary Firmware Structure
 =========================
 
@@ -340,6 +781,48 @@ We also expect that platform-specific resource entries will show up
 at some point. When that happens, we could easily add a new RSC_PLATFORM
 type, and hand those resources to the platform-specific rproc driver to handle.
 
+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`.
+
 Virtio and remoteproc
 =====================
 
-- 
2.39.3 (Apple Git-146)

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