[RFC PATCH 5/8] media: Document the media request API

[Alexandre Courbot <acourbot@chromium.org>]

From: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

The media request API is made of a new ioctl to implement request
management. Document it.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
[acourbot@chromium.org: adapt for newest API]
Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
---
 Documentation/media/uapi/mediactl/media-funcs.rst  |   1 +
 .../media/uapi/mediactl/media-ioc-request-cmd.rst  | 140 +++++++++++++++++++++
 2 files changed, 141 insertions(+)
 create mode 100644 Documentation/media/uapi/mediactl/media-ioc-request-cmd.rst

diff --git a/Documentation/media/uapi/mediactl/media-funcs.rst b/Documentation/media/uapi/mediactl/media-funcs.rst
index 076856501cdb..e3a45d82ffcb 100644
--- a/Documentation/media/uapi/mediactl/media-funcs.rst
+++ b/Documentation/media/uapi/mediactl/media-funcs.rst
@@ -15,4 +15,5 @@ Function Reference
     media-ioc-g-topology
     media-ioc-enum-entities
     media-ioc-enum-links
+    media-ioc-request-cmd
     media-ioc-setup-link
diff --git a/Documentation/media/uapi/mediactl/media-ioc-request-cmd.rst b/Documentation/media/uapi/mediactl/media-ioc-request-cmd.rst
new file mode 100644
index 000000000000..17223e8170e9
--- /dev/null
+++ b/Documentation/media/uapi/mediactl/media-ioc-request-cmd.rst
@@ -0,0 +1,140 @@
+.. -*- coding: utf-8; mode: rst -*-
+
+.. _media_ioc_request_cmd:
+
+***************************
+ioctl MEDIA_IOC_REQUEST_CMD
+***************************
+
+Name
+====
+
+MEDIA_IOC_REQUEST_CMD - Manage media device requests
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, MEDIA_IOC_REQUEST_CMD, struct media_request_cmd *argp )
+    :name: MEDIA_IOC_REQUEST_CMD
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <media-func-open>`.
+
+``argp``
+
+
+Description
+===========
+
+The MEDIA_IOC_REQUEST_CMD ioctl allow applications to manage media device
+requests. A request is an object that can group media device configuration
+parameters, including subsystem-specific parameters, in order to apply all the
+parameters atomically. Applications are responsible for allocating and
+deleting requests, filling them with configuration parameters submitting them.
+
+Request operations are performed by calling the MEDIA_IOC_REQUEST_CMD ioctl
+with a pointer to a struct :c:type:`media_request_cmd` with the cmd field set
+to the appropriate command. :ref:`media-request-command` lists the commands
+supported by the ioctl.
+
+The struct :c:type:`media_request_cmd` request field contains the file
+descriptorof the request on which the command operates. For the
+``MEDIA_REQ_CMD_ALLOC`` command the field is set to zero by applications and
+filled by the driver. For all other commands the field is set by applications
+and left untouched by the driver.
+
+To allocate a new request applications use the ``MEDIA_REQ_CMD_ALLOC``
+command. The driver will allocate a new request and return its ID in the
+request field.
+
+Requests are reference-counted. A newly allocated request is referenced
+by the returned file descriptor, and can be later referenced by
+subsystem-specific operations. Requests will thus be automatically deleted
+when they're not longer used after the returned file descriptor is closed.
+
+If a request isn't needed applications can delete it by calling ``close()``
+on it. The driver will drop the file handle reference. The request will not
+be usable through the MEDIA_IOC_REQUEST_CMD ioctl anymore, but will only be
+deleted when the last reference is released. If no other reference exists when
+``close()`` is invoked the request will be deleted immediately.
+
+After creating a request applications should fill it with configuration
+parameters. This is performed through subsystem-specific request APIs outside
+the scope of the media controller API. See the appropriate subsystem APIs for
+more information, including how they interact with the MEDIA_IOC_REQUEST_CMD
+ioctl.
+
+Once a request contains all the desired configuration parameters it can be
+submitted using the ``MEDIA_REQ_CMD_SUBMIT`` command. This will let the
+buffers queued for the request be passed to their respective drivers, which
+will then apply the request's parameters before processing them.
+
+Once a request has been queued applications are not allowed to modify its
+configuration parameters until the request has been fully processed. Any
+attempt to do so will result in the related subsystem API returning an error.
+The application that submitted the request can wait for its completion by
+polling on the request's file descriptor.
+
+Once a request has completed, it can be reused. The ``MEDIA_REQ_CMD_REINIT``
+command will bring it back to its initial state, so it can be prepared and
+submitted again.
+
+.. c:type:: media_request_cmd
+
+.. flat-table:: struct media_request_cmd
+    :header-rows:  0
+    :stub-columns: 0
+    :widths: 1 2 8
+
+    * - __u32
+      - ``cmd``
+      - Command, set by the application. See below for the list of supported
+        commands.
+    * - __u32
+      - ``fd``
+      - Request FD, set by the driver for the MEDIA_REQ_CMD_ALLOC command and
+        by the application for all other commands.
+
+
+.. _media-request-command:
+
+.. cssclass:: longtable
+
+.. flat-table:: Media request commands
+    :header-rows:  0
+    :stub-columns: 0
+
+    * .. _MEDIA-REQ-CMD-ALLOC:
+
+      - ``MEDIA_REQ_CMD_ALLOC``
+      - Allocate a new request.
+    * .. _MEDIA-REQ-CMD-SUBMIT:
+
+      - ``MEDIA_REQ_CMD_SUBMIT``
+      - Submit a request to be processed.
+    * .. _MEDIA-REQ-CMD-QUEUE:
+
+      - ``MEDIA_REQ_CMD_REINIT``
+      - Reinitializes a completed request.
+
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.
+
+EINVAL
+    The struct :c:type:`media_request_cmd` specifies an invalid command or
+    references a non-existing request.
+
+ENOSYS
+    The struct :c:type:`media_request_cmd` specifies the
+    ``MEDIA_REQ_CMD_QUEUE`` or ``MEDIA_REQ_CMD_APPLY`` command and that
+    command isn't implemented by the device.
-- 
2.16.0.rc1.238.g530d649a79-goog