Merge tag 'media/v4.20-2' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media

Pull new experimental media request API from Mauro Carvalho Chehab:
 "A new media request API

  This API is needed to support device drivers that can dynamically
  change their parameters for each new frame. The latest versions of
  Google camera and codec HAL depends on such feature.

  At this stage, it supports only stateless codecs.

  It has been discussed for a long time (at least over the last 3-4
  years), and we finally reached to something that seem to work.

  This series contain both the API and core changes required to support
  it and a new m2m decoder driver (cedrus).

  As the current API is still experimental, the only real driver using
  it (cedrus) was added at staging[1]. We intend to keep it there for a
  while, in order to test the API. Only when we're sure that this API
  works for other cases (like encoders), we'll move this driver out of
  staging and set the API into a stone.

  [1] We added support for the vivid virtual driver (used only for
  testing) to it too, as it makes easier to test the API for the ones
  that don't have the cedrus hardware"

* tag 'media/v4.20-2' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (53 commits)
  media: dt-bindings: Document the Rockchip VPU bindings
  media: platform: Add Cedrus VPU decoder driver
  media: dt-bindings: media: Document bindings for the Cedrus VPU driver
  media: v4l: Add definition for the Sunxi tiled NV12 format
  media: v4l: Add definitions for MPEG-2 slice format and metadata
  media: videobuf2-core: Rework and rename helper for request buffer count
  media: v4l2-ctrls.c: initialize an error return code with zero
  media: v4l2-compat-ioctl32.c: add missing documentation for a field
  media: media-request: update documentation
  media: media-request: EPERM -> EACCES/EBUSY
  media: v4l2-ctrls: improve media_request_(un)lock_for_update
  media: v4l2-ctrls: use media_request_(un)lock_for_access
  media: media-request: add media_request_(un)lock_for_access
  media: vb2: set reqbufs/create_bufs capabilities
  media: videodev2.h: add new capabilities for buffer types
  media: buffer.rst: only set V4L2_BUF_FLAG_REQUEST_FD for QBUF
  media: v4l2-ctrls: return -EACCES if request wasn't completed
  media: media-request: return -EINVAL for invalid request_fds
  media: vivid: add request support
  media: vivid: add mc
  ...

9 files changed, 647 insertions, 0 deletions

diff --git a/Documentation/media/uapi/mediactl/media-controller.rst b/Documentation/media/uapi/mediactl/media-controller.rst
index 0eea4f9a07d5..66aff38cd499 100644
--- a/Documentation/media/uapi/mediactl/media-controller.rst
+++ b/Documentation/media/uapi/mediactl/media-controller.rst
@@ -21,6 +21,7 @@ Part IV - Media Controller API
     media-controller-intro
     media-controller-model
     media-types
+    request-api
     media-funcs
     media-header
 
diff --git a/Documentation/media/uapi/mediactl/media-funcs.rst b/Documentation/media/uapi/mediactl/media-funcs.rst
index 076856501cdb..260f9dcadcde 100644
--- a/Documentation/media/uapi/mediactl/media-funcs.rst
+++ b/Documentation/media/uapi/mediactl/media-funcs.rst
@@ -16,3 +16,9 @@ Function Reference
     media-ioc-enum-entities
     media-ioc-enum-links
     media-ioc-setup-link
+    media-ioc-request-alloc
+    request-func-close
+    request-func-ioctl
+    request-func-poll
+    media-request-ioc-queue
+    media-request-ioc-reinit
diff --git a/Documentation/media/uapi/mediactl/media-ioc-request-alloc.rst b/Documentation/media/uapi/mediactl/media-ioc-request-alloc.rst
new file mode 100644
index 000000000000..0f8b31874002
--- /dev/null
+++ b/Documentation/media/uapi/mediactl/media-ioc-request-alloc.rst
@@ -0,0 +1,66 @@
+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _media_ioc_request_alloc:
+
+*****************************
+ioctl MEDIA_IOC_REQUEST_ALLOC
+*****************************
+
+Name
+====
+
+MEDIA_IOC_REQUEST_ALLOC - Allocate a request
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, MEDIA_IOC_REQUEST_ALLOC, int *argp )
+    :name: MEDIA_IOC_REQUEST_ALLOC
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <media-func-open>`.
+
+``argp``
+    Pointer to an integer.
+
+
+Description
+===========
+
+If the media device supports :ref:`requests <media-request-api>`, then
+this ioctl can be used to allocate a request. If it is not supported, then
+``errno`` is set to ``ENOTTY``. A request is accessed through a file descriptor
+that is returned in ``*argp``.
+
+If the request was successfully allocated, then the request file descriptor
+can be passed to the :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`,
+:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
+:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and
+:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls.
+
+In addition, the request can be queued by calling
+:ref:`MEDIA_REQUEST_IOC_QUEUE` and re-initialized by calling
+:ref:`MEDIA_REQUEST_IOC_REINIT`.
+
+Finally, the file descriptor can be :ref:`polled <request-func-poll>` to wait
+for the request to complete.
+
+The request will remain allocated until all the file descriptors associated
+with it are closed by :ref:`close() <request-func-close>` and the driver no
+longer uses the request internally. See also
+:ref:`here <media-request-life-time>` for more information.
+
+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.
+
+ENOTTY
+    The driver has no support for requests.
diff --git a/Documentation/media/uapi/mediactl/media-request-ioc-queue.rst b/Documentation/media/uapi/mediactl/media-request-ioc-queue.rst
new file mode 100644
index 000000000000..6dd2d7fea714
--- /dev/null
+++ b/Documentation/media/uapi/mediactl/media-request-ioc-queue.rst
@@ -0,0 +1,78 @@
+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _media_request_ioc_queue:
+
+*****************************
+ioctl MEDIA_REQUEST_IOC_QUEUE
+*****************************
+
+Name
+====
+
+MEDIA_REQUEST_IOC_QUEUE - Queue a request
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int request_fd, MEDIA_REQUEST_IOC_QUEUE )
+    :name: MEDIA_REQUEST_IOC_QUEUE
+
+
+Arguments
+=========
+
+``request_fd``
+    File descriptor returned by :ref:`MEDIA_IOC_REQUEST_ALLOC`.
+
+
+Description
+===========
+
+If the media device supports :ref:`requests <media-request-api>`, then
+this request ioctl can be used to queue a previously allocated request.
+
+If the request was successfully queued, then the file descriptor can be
+:ref:`polled <request-func-poll>` to wait for the request to complete.
+
+If the request was already queued before, then ``EBUSY`` is returned.
+Other errors can be returned if the contents of the request contained
+invalid or inconsistent data, see the next section for a list of
+common error codes. On error both the request and driver state are unchanged.
+
+Once a request is queued, then the driver is required to gracefully handle
+errors that occur when the request is applied to the hardware. The
+exception is the ``EIO`` error which signals a fatal error that requires
+the application to stop streaming to reset the hardware state.
+
+It is not allowed to mix queuing requests with queuing buffers directly
+(without a request). ``EBUSY`` will be returned if the first buffer was
+queued directly and you next try to queue a request, or vice versa.
+
+A request must contain at least one buffer, otherwise this ioctl will
+return an ``ENOENT`` error.
+
+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.
+
+EBUSY
+    The request was already queued or the application queued the first
+    buffer directly, but later attempted to use a request. It is not permitted
+    to mix the two APIs.
+ENOENT
+    The request did not contain any buffers. All requests are required
+    to have at least one buffer. This can also be returned if some required
+    configuration is missing in the request.
+ENOMEM
+    Out of memory when allocating internal data structures for this
+    request.
+EINVAL
+    The request has invalid data.
+EIO
+    The hardware is in a bad state. To recover, the application needs to
+    stop streaming to reset the hardware state and then try to restart
+    streaming.
diff --git a/Documentation/media/uapi/mediactl/media-request-ioc-reinit.rst b/Documentation/media/uapi/mediactl/media-request-ioc-reinit.rst
new file mode 100644
index 000000000000..febe888494c8
--- /dev/null
+++ b/Documentation/media/uapi/mediactl/media-request-ioc-reinit.rst
@@ -0,0 +1,51 @@
+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _media_request_ioc_reinit:
+
+******************************
+ioctl MEDIA_REQUEST_IOC_REINIT
+******************************
+
+Name
+====
+
+MEDIA_REQUEST_IOC_REINIT - Re-initialize a request
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int request_fd, MEDIA_REQUEST_IOC_REINIT )
+    :name: MEDIA_REQUEST_IOC_REINIT
+
+
+Arguments
+=========
+
+``request_fd``
+    File descriptor returned by :ref:`MEDIA_IOC_REQUEST_ALLOC`.
+
+Description
+===========
+
+If the media device supports :ref:`requests <media-request-api>`, then
+this request ioctl can be used to re-initialize a previously allocated
+request.
+
+Re-initializing a request will clear any existing data from the request.
+This avoids having to :ref:`close() <request-func-close>` a completed
+request and allocate a new request. Instead the completed request can just
+be re-initialized and it is ready to be used again.
+
+A request can only be re-initialized if it either has not been queued
+yet, or if it was queued and completed. Otherwise it will set ``errno``
+to ``EBUSY``. No other error codes can be returned.
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately.
+
+EBUSY
+    The request is queued but not yet completed.
diff --git a/Documentation/media/uapi/mediactl/request-api.rst b/Documentation/media/uapi/mediactl/request-api.rst
new file mode 100644
index 000000000000..5f4a23029c48
--- /dev/null
+++ b/Documentation/media/uapi/mediactl/request-api.rst
@@ -0,0 +1,252 @@
+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _media-request-api:
+
+Request API
+===========
+
+The Request API has been designed to allow V4L2 to deal with requirements of
+modern devices (stateless codecs, complex camera pipelines, ...) and APIs
+(Android Codec v2). One such requirement is the ability for devices belonging to
+the same pipeline to reconfigure and collaborate closely on a per-frame basis.
+Another is support of stateless codecs, which require controls to be applied
+to specific frames (aka 'per-frame controls') in order to be used efficiently.
+
+While the initial use-case was V4L2, it can be extended to other subsystems
+as well, as long as they use the media controller.
+
+Supporting these features without the Request API is not always possible and if
+it is, it is terribly inefficient: user-space would have to flush all activity
+on the media pipeline, reconfigure it for the next frame, queue the buffers to
+be processed with that configuration, and wait until they are all available for
+dequeuing before considering the next frame. This defeats the purpose of having
+buffer queues since in practice only one buffer would be queued at a time.
+
+The Request API allows a specific configuration of the pipeline (media
+controller topology + configuration for each media entity) to be associated with
+specific buffers. This allows user-space to schedule several tasks ("requests")
+with different configurations in advance, knowing that the configuration will be
+applied when needed to get the expected result. Configuration values at the time
+of request completion are also available for reading.
+
+Usage
+=====
+
+The Request API extends the Media Controller API and cooperates with
+subsystem-specific APIs to support request usage. At the Media Controller
+level, requests are allocated from the supporting Media Controller device
+node. Their life cycle is then managed through the request file descriptors in
+an opaque way. Configuration data, buffer handles and processing results
+stored in requests are accessed through subsystem-specific APIs extended for
+request support, such as V4L2 APIs that take an explicit ``request_fd``
+parameter.
+
+Request Allocation
+------------------
+
+User-space allocates requests using :ref:`MEDIA_IOC_REQUEST_ALLOC`
+for the media device node. This returns a file descriptor representing the
+request. Typically, several such requests will be allocated.
+
+Request Preparation
+-------------------
+
+Standard V4L2 ioctls can then receive a request file descriptor to express the
+fact that the ioctl is part of said request, and is not to be applied
+immediately. See :ref:`MEDIA_IOC_REQUEST_ALLOC` for a list of ioctls that
+support this. Configurations set with a ``request_fd`` parameter are stored
+instead of being immediately applied, and buffers queued to a request do not
+enter the regular buffer queue until the request itself is queued.
+
+Request Submission
+------------------
+
+Once the configuration and buffers of the request are specified, it can be
+queued by calling :ref:`MEDIA_REQUEST_IOC_QUEUE` on the request file descriptor.
+A request must contain at least one buffer, otherwise ``ENOENT`` is returned.
+A queued request cannot be modified anymore.
+
+.. caution::
+   For :ref:`memory-to-memory devices <codec>` you can use requests only for
+   output buffers, not for capture buffers. Attempting to add a capture buffer
+   to a request will result in an ``EACCES`` error.
+
+If the request contains configurations for multiple entities, individual drivers
+may synchronize so the requested pipeline's topology is applied before the
+buffers are processed. Media controller drivers do a best effort implementation
+since perfect atomicity may not be possible due to hardware limitations.
+
+.. caution::
+
+   It is not allowed to mix queuing requests with directly queuing buffers:
+   whichever method is used first locks this in place until
+   :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` is called or the device is
+   :ref:`closed <func-close>`. Attempts to directly queue a buffer when earlier
+   a buffer was queued via a request or vice versa will result in an ``EBUSY``
+   error.
+
+Controls can still be set without a request and are applied immediately,
+regardless of whether a request is in use or not.
+
+.. caution::
+
+   Setting the same control through a request and also directly can lead to
+   undefined behavior!
+
+User-space can :ref:`poll() <request-func-poll>` a request file descriptor in
+order to wait until the request completes. A request is considered complete
+once all its associated buffers are available for dequeuing and all the
+associated controls have been updated with the values at the time of completion.
+Note that user-space does not need to wait for the request to complete to
+dequeue its buffers: buffers that are available halfway through a request can
+be dequeued independently of the request's state.
+
+A completed request contains the state of the device after the request was
+executed. User-space can query that state by calling
+:ref:`ioctl VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with the request file
+descriptor. Calling :ref:`ioctl VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` for a
+request that has been queued but not yet completed will return ``EBUSY``
+since the control values might be changed at any time by the driver while the
+request is in flight.
+
+.. _media-request-life-time:
+
+Recycling and Destruction
+-------------------------
+
+Finally, a completed request can either be discarded or be reused. Calling
+:ref:`close() <request-func-close>` on a request file descriptor will make
+that file descriptor unusable and the request will be freed once it is no
+longer in use by the kernel. That is, if the request is queued and then the
+file descriptor is closed, then it won't be freed until the driver completed
+the request.
+
+The :ref:`MEDIA_REQUEST_IOC_REINIT` will clear a request's state and make it
+available again. No state is retained by this operation: the request is as
+if it had just been allocated.
+
+Example for a Codec Device
+--------------------------
+
+For use-cases such as :ref:`codecs <codec>`, the request API can be used
+to associate specific controls to
+be applied by the driver for the OUTPUT buffer, allowing user-space
+to queue many such buffers in advance. It can also take advantage of requests'
+ability to capture the state of controls when the request completes to read back
+information that may be subject to change.
+
+Put into code, after obtaining a request, user-space can assign controls and one
+OUTPUT buffer to it:
+
+.. code-block:: c
+
+	struct v4l2_buffer buf;
+	struct v4l2_ext_controls ctrls;
+	int req_fd;
+	...
+	if (ioctl(media_fd, MEDIA_IOC_REQUEST_ALLOC, &req_fd))
+		return errno;
+	...
+	ctrls.which = V4L2_CTRL_WHICH_REQUEST_VAL;
+	ctrls.request_fd = req_fd;
+	if (ioctl(codec_fd, VIDIOC_S_EXT_CTRLS, &ctrls))
+		return errno;
+	...
+	buf.type = V4L2_BUF_TYPE_VIDEO_OUTPUT;
+	buf.flags |= V4L2_BUF_FLAG_REQUEST_FD;
+	buf.request_fd = req_fd;
+	if (ioctl(codec_fd, VIDIOC_QBUF, &buf))
+		return errno;
+
+Note that it is not allowed to use the Request API for CAPTURE buffers
+since there are no per-frame settings to report there.
+
+Once the request is fully prepared, it can be queued to the driver:
+
+.. code-block:: c
+
+	if (ioctl(req_fd, MEDIA_REQUEST_IOC_QUEUE))
+		return errno;
+
+User-space can then either wait for the request to complete by calling poll() on
+its file descriptor, or start dequeuing CAPTURE buffers. Most likely, it will
+want to get CAPTURE buffers as soon as possible and this can be done using a
+regular :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`:
+
+.. code-block:: c
+
+	struct v4l2_buffer buf;
+
+	memset(&buf, 0, sizeof(buf));
+	buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+	if (ioctl(codec_fd, VIDIOC_DQBUF, &buf))
+		return errno;
+
+Note that this example assumes for simplicity that for every OUTPUT buffer
+there will be one CAPTURE buffer, but this does not have to be the case.
+
+We can then, after ensuring that the request is completed via polling the
+request file descriptor, query control values at the time of its completion via
+a call to :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
+This is particularly useful for volatile controls for which we want to
+query values as soon as the capture buffer is produced.
+
+.. code-block:: c
+
+	struct pollfd pfd = { .events = POLLPRI, .fd = req_fd };
+	poll(&pfd, 1, -1);
+	...
+	ctrls.which = V4L2_CTRL_WHICH_REQUEST_VAL;
+	ctrls.request_fd = req_fd;
+	if (ioctl(codec_fd, VIDIOC_G_EXT_CTRLS, &ctrls))
+		return errno;
+
+Once we don't need the request anymore, we can either recycle it for reuse with
+:ref:`MEDIA_REQUEST_IOC_REINIT`...
+
+.. code-block:: c
+
+	if (ioctl(req_fd, MEDIA_REQUEST_IOC_REINIT))
+		return errno;
+
+... or close its file descriptor to completely dispose of it.
+
+.. code-block:: c
+
+	close(req_fd);
+
+Example for a Simple Capture Device
+-----------------------------------
+
+With a simple capture device, requests can be used to specify controls to apply
+for a given CAPTURE buffer.
+
+.. code-block:: c
+
+	struct v4l2_buffer buf;
+	struct v4l2_ext_controls ctrls;
+	int req_fd;
+	...
+	if (ioctl(media_fd, MEDIA_IOC_REQUEST_ALLOC, &req_fd))
+		return errno;
+	...
+	ctrls.which = V4L2_CTRL_WHICH_REQUEST_VAL;
+	ctrls.request_fd = req_fd;
+	if (ioctl(camera_fd, VIDIOC_S_EXT_CTRLS, &ctrls))
+		return errno;
+	...
+	buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+	buf.flags |= V4L2_BUF_FLAG_REQUEST_FD;
+	buf.request_fd = req_fd;
+	if (ioctl(camera_fd, VIDIOC_QBUF, &buf))
+		return errno;
+
+Once the request is fully prepared, it can be queued to the driver:
+
+.. code-block:: c
+
+	if (ioctl(req_fd, MEDIA_REQUEST_IOC_QUEUE))
+		return errno;
+
+User-space can then dequeue buffers, wait for the request completion, query
+controls and recycle the request as in the M2M example above.
diff --git a/Documentation/media/uapi/mediactl/request-func-close.rst b/Documentation/media/uapi/mediactl/request-func-close.rst
new file mode 100644
index 000000000000..098d7f2b9548
--- /dev/null
+++ b/Documentation/media/uapi/mediactl/request-func-close.rst
@@ -0,0 +1,49 @@
+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _request-func-close:
+
+***************
+request close()
+***************
+
+Name
+====
+
+request-close - Close a request file descriptor
+
+
+Synopsis
+========
+
+.. code-block:: c
+
+    #include <unistd.h>
+
+
+.. c:function:: int close( int fd )
+    :name: req-close
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`MEDIA_IOC_REQUEST_ALLOC`.
+
+
+Description
+===========
+
+Closes the request file descriptor. Resources associated with the request
+are freed once all file descriptors associated with the request are closed
+and the driver has completed the request.
+See :ref:`here <media-request-life-time>` for more information.
+
+
+Return Value
+============
+
+:ref:`close() <request-func-close>` returns 0 on success. On error, -1 is
+returned, and ``errno`` is set appropriately. Possible error codes are:
+
+EBADF
+    ``fd`` is not a valid open file descriptor.
diff --git a/Documentation/media/uapi/mediactl/request-func-ioctl.rst b/Documentation/media/uapi/mediactl/request-func-ioctl.rst
new file mode 100644
index 000000000000..ff7b072a6999
--- /dev/null
+++ b/Documentation/media/uapi/mediactl/request-func-ioctl.rst
@@ -0,0 +1,67 @@
+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _request-func-ioctl:
+
+***************
+request ioctl()
+***************
+
+Name
+====
+
+request-ioctl - Control a request file descriptor
+
+
+Synopsis
+========
+
+.. code-block:: c
+
+    #include <sys/ioctl.h>
+
+
+.. c:function:: int ioctl( int fd, int cmd, void *argp )
+    :name: req-ioctl
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`MEDIA_IOC_REQUEST_ALLOC`.
+
+``cmd``
+    The request ioctl command code as defined in the media.h header file, for
+    example :ref:`MEDIA_REQUEST_IOC_QUEUE`.
+
+``argp``
+    Pointer to a request-specific structure.
+
+
+Description
+===========
+
+The :ref:`ioctl() <request-func-ioctl>` function manipulates request
+parameters. The argument ``fd`` must be an open file descriptor.
+
+The ioctl ``cmd`` code specifies the request function to be called. It
+has encoded in it whether the argument is an input, output or read/write
+parameter, and the size of the argument ``argp`` in bytes.
+
+Macros and structures definitions specifying request ioctl commands and
+their parameters are located in the media.h header file. All request ioctl
+commands, their respective function and parameters are specified in
+:ref:`media-user-func`.
+
+
+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.
+
+Command-specific error codes are listed in the individual command
+descriptions.
+
+When an ioctl that takes an output or read/write parameter fails, the
+parameter remains unmodified.
diff --git a/Documentation/media/uapi/mediactl/request-func-poll.rst b/Documentation/media/uapi/mediactl/request-func-poll.rst
new file mode 100644
index 000000000000..85191254f381
--- /dev/null
+++ b/Documentation/media/uapi/mediactl/request-func-poll.rst
@@ -0,0 +1,77 @@
+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _request-func-poll:
+
+**************
+request poll()
+**************
+
+Name
+====
+
+request-poll - Wait for some event on a file descriptor
+
+
+Synopsis
+========
+
+.. code-block:: c
+
+    #include <sys/poll.h>
+
+
+.. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout )
+   :name: request-poll
+
+Arguments
+=========
+
+``ufds``
+   List of file descriptor events to be watched
+
+``nfds``
+   Number of file descriptor events at the \*ufds array
+
+``timeout``
+   Timeout to wait for events
+
+
+Description
+===========
+
+With the :c:func:`poll() <request-func-poll>` function applications can wait
+for a request to complete.
+
+On success :c:func:`poll() <request-func-poll>` returns the number of file
+descriptors that have been selected (that is, file descriptors for which the
+``revents`` field of the respective struct :c:type:`pollfd`
+is non-zero). Request file descriptor set the ``POLLPRI`` flag in ``revents``
+when the request was completed.  When the function times out it returns
+a value of zero, on failure it returns -1 and the ``errno`` variable is
+set appropriately.
+
+Attempting to poll for a request that is not yet queued will
+set the ``POLLERR`` flag in ``revents``.
+
+
+Return Value
+============
+
+On success, :c:func:`poll() <request-func-poll>` returns the number of
+structures which have non-zero ``revents`` fields, or zero if the call
+timed out. On error -1 is returned, and the ``errno`` variable is set
+appropriately:
+
+``EBADF``
+    One or more of the ``ufds`` members specify an invalid file
+    descriptor.
+
+``EFAULT``
+    ``ufds`` references an inaccessible memory area.
+
+``EINTR``
+    The call was interrupted by a signal.
+
+``EINVAL``
+    The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use
+    ``getrlimit()`` to obtain this value.