diff options
Diffstat (limited to 'Documentation/media/uapi/v4l/vidioc-qbuf.rst')
| -rw-r--r-- | Documentation/media/uapi/v4l/vidioc-qbuf.rst | 37 |
1 files changed, 35 insertions, 2 deletions
diff --git a/Documentation/media/uapi/v4l/vidioc-qbuf.rst b/Documentation/media/uapi/v4l/vidioc-qbuf.rst index 9e448a4aa3aa..753b3b5946b1 100644 --- a/Documentation/media/uapi/v4l/vidioc-qbuf.rst +++ b/Documentation/media/uapi/v4l/vidioc-qbuf.rst @@ -65,7 +65,7 @@ To enqueue a :ref:`memory mapped <mmap>` buffer applications set the with a pointer to this structure the driver sets the ``V4L2_BUF_FLAG_MAPPED`` and ``V4L2_BUF_FLAG_QUEUED`` flags and clears the ``V4L2_BUF_FLAG_DONE`` flag in the ``flags`` field, or it returns an -EINVAL error code. +``EINVAL`` error code. To enqueue a :ref:`user pointer <userp>` buffer applications set the ``memory`` field to ``V4L2_MEMORY_USERPTR``, the ``m.userptr`` field to @@ -98,6 +98,28 @@ dequeued, until the :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` or :ref:`VIDIOC_REQBUFS` ioctl is called, or until the device is closed. +The ``request_fd`` field can be used with the ``VIDIOC_QBUF`` ioctl to specify +the file descriptor of a :ref:`request <media-request-api>`, if requests are +in use. Setting it means that the buffer will not be passed to the driver +until the request itself is queued. Also, the driver will apply any +settings associated with the request for this buffer. This field will +be ignored unless the ``V4L2_BUF_FLAG_REQUEST_FD`` flag is set. +If the device does not support requests, then ``EACCES`` will be returned. +If requests are supported but an invalid request file descriptor is given, +then ``EINVAL`` will be returned. + +.. caution:: + It is not allowed to mix queuing requests with queuing buffers directly. + ``EBUSY`` will be returned if the first buffer was queued directly and + then the application tries to queue a request, or vice versa. After + closing the file descriptor, calling + :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` or calling :ref:`VIDIOC_REQBUFS` + the check for this will be reset. + + For :ref:`memory-to-memory devices <codec>` you can specify the + ``request_fd`` only for output buffers, not for capture buffers. Attempting + to specify this for a capture buffer will result in an ``EACCES`` error. + Applications call the ``VIDIOC_DQBUF`` ioctl to dequeue a filled (capturing) or displayed (output) buffer from the driver's outgoing queue. They just set the ``type``, ``memory`` and ``reserved`` fields of @@ -133,7 +155,9 @@ EAGAIN EINVAL The buffer ``type`` is not supported, or the ``index`` is out of bounds, or no buffers have been allocated yet, or the ``userptr`` or - ``length`` are invalid. + ``length`` are invalid, or the ``V4L2_BUF_FLAG_REQUEST_FD`` flag was + set but the the given ``request_fd`` was invalid, or ``m.fd`` was + an invalid DMABUF file descriptor. EIO ``VIDIOC_DQBUF`` failed due to an internal error. Can also indicate @@ -153,3 +177,12 @@ EPIPE ``VIDIOC_DQBUF`` returns this on an empty capture queue for mem2mem codecs if a buffer with the ``V4L2_BUF_FLAG_LAST`` was already dequeued and no new buffers are expected to become available. + +EACCES + The ``V4L2_BUF_FLAG_REQUEST_FD`` flag was set but the device does not + support requests for the given buffer type. + +EBUSY + The first buffer was queued via a request, but the application now tries + to queue it directly, or vice versa (it is not permitted to mix the two + APIs). |