Re: [PATCH v7 6/6] [media] v4l: Document explicit synchronization behavior
On 01/10/18 17:07, Gustavo Padovan wrote: > From: Gustavo Padovan> > Add section to VIDIOC_QBUF about it > > v5: > - Remove V4L2_CAP_ORDERED > - Add doc about V4L2_FMT_FLAG_UNORDERED > > v4: > - Document ordering behavior for in-fences > - Document V4L2_CAP_ORDERED capability > - Remove doc about OUT_FENCE event > - Document immediate return of out-fence in QBUF > > v3: > - make the out_fence refer to the current buffer (Hans) > - Note what happens when the IN_FENCE is not set (Hans) > > v2: > - mention that fences are files (Hans) > - rework for the new API > > Signed-off-by: Gustavo Padovan > --- > Documentation/media/uapi/v4l/vidioc-qbuf.rst | 47 > +++- > Documentation/media/uapi/v4l/vidioc-querybuf.rst | 9 - > 2 files changed, 54 insertions(+), 2 deletions(-) > > diff --git a/Documentation/media/uapi/v4l/vidioc-qbuf.rst > b/Documentation/media/uapi/v4l/vidioc-qbuf.rst > index 9e448a4aa3aa..8809397fb110 100644 > --- a/Documentation/media/uapi/v4l/vidioc-qbuf.rst > +++ b/Documentation/media/uapi/v4l/vidioc-qbuf.rst > @@ -54,7 +54,7 @@ When the buffer is intended for output (``type`` is > or ``V4L2_BUF_TYPE_VBI_OUTPUT``) applications must also initialize the > ``bytesused``, ``field`` and ``timestamp`` fields, see :ref:`buffer` > for details. Applications must also set ``flags`` to 0. The > -``reserved2`` and ``reserved`` fields must be set to 0. When using the > +``reserved`` field must be set to 0. When using the > :ref:`multi-planar API `, the ``m.planes`` field must > contain a userspace pointer to a filled-in array of struct > :c:type:`v4l2_plane` and the ``length`` field must be set > @@ -118,6 +118,51 @@ immediately with an ``EAGAIN`` error code when no buffer > is available. > The struct :c:type:`v4l2_buffer` structure is specified in > :ref:`buffer`. > > +Explicit Synchronization > + > + > +Explicit Synchronization allows us to control the synchronization of > +shared buffers from userspace by passing fences to the kernel and/or > +receiving them from it. Fences passed to the kernel are named in-fences and > +the kernel should wait on them to signal before using the buffer, i.e., > queueing > +it to the driver. I would drop ", i.e., queueing it to the driver" On the other side, the kernel can create out-fences for the > +buffers it queues to the drivers. Out-fences signal when the driver is > +finished with buffer, i.e., the buffer is ready. The fences are represented > +as a file and passed as a file descriptor to userspace. > + > +The in-fences are communicated to the kernel at the ``VIDIOC_QBUF`` ioctl > +using the ``V4L2_BUF_FLAG_IN_FENCE`` buffer flag and the `fence_fd` field. If > +an in-fence needs to be passed to the kernel, `fence_fd` should be set to the > +fence file descriptor number and the ``V4L2_BUF_FLAG_IN_FENCE`` should be set > +as well. Setting one but not the other will cause ``VIDIOC_QBUF`` to return > +with error. The fence_fd field will be ignored if the with -> with an > +``V4L2_BUF_FLAG_IN_FENCE`` is not set. > + > +The videobuf2-core will guarantee that all buffers queued with in-fence will with -> with an > +be queued to the drivers in the same order. Fence may signal out of order, so Fence -> Fences > +this guarantee at videobuf2 is necessary to not change ordering. Add some text here to make it clear that waiting for a buffer with an in-fence will also block all buffers queued after that buffer. > + > +If the in-fence signals with an error the videobuf2 won't queue the buffer to > +the driver, instead it will flag it with an error. And then wait for the > +previous buffer to complete before asking userspace dequeue the buffer with > +error - to make sure we deliver the buffers back in the correct order. I think there is no need to describe the internal implementation. It is enough to say that the buffer is marked with FLAG_ERROR if the in-fence signals an error. > + > +To get an out-fence back from V4L2 the ``V4L2_BUF_FLAG_OUT_FENCE`` flag > should > +be set to ask for a fence to be attached to the buffer. The out-fence fd is > +sent to userspace as a ``VIDIOC_QBUF`` return argument on the `fence_fd` > field. > + > +Note the the same `fence_fd` field is used for both sending the in-fence as > +input argument to receive the out-fence as a return argument. > + > +At streamoff the out-fences will either signal normally if the driver waits > +for the operations on the buffers to finish or signal with an error if the > +driver cancels the pending operations. Buffers with in-fences won't be queued > +to the driver if their fences signal. It will be cleaned up. It -> They It should be clarified here if you can or cannot use both in and out fences for the same buffer. > + > +The ``V4L2_FMT_FLAG_UNORDERED`` flag in ``VIDIOC_ENUM_FMT`` tells userspace > +that
Re: [PATCH v7 6/6] [media] v4l: Document explicit synchronization behavior
On 01/10/18 17:07, Gustavo Padovan wrote: > From: Gustavo Padovan > > Add section to VIDIOC_QBUF about it > > v5: > - Remove V4L2_CAP_ORDERED > - Add doc about V4L2_FMT_FLAG_UNORDERED > > v4: > - Document ordering behavior for in-fences > - Document V4L2_CAP_ORDERED capability > - Remove doc about OUT_FENCE event > - Document immediate return of out-fence in QBUF > > v3: > - make the out_fence refer to the current buffer (Hans) > - Note what happens when the IN_FENCE is not set (Hans) > > v2: > - mention that fences are files (Hans) > - rework for the new API > > Signed-off-by: Gustavo Padovan > --- > Documentation/media/uapi/v4l/vidioc-qbuf.rst | 47 > +++- > Documentation/media/uapi/v4l/vidioc-querybuf.rst | 9 - > 2 files changed, 54 insertions(+), 2 deletions(-) > > diff --git a/Documentation/media/uapi/v4l/vidioc-qbuf.rst > b/Documentation/media/uapi/v4l/vidioc-qbuf.rst > index 9e448a4aa3aa..8809397fb110 100644 > --- a/Documentation/media/uapi/v4l/vidioc-qbuf.rst > +++ b/Documentation/media/uapi/v4l/vidioc-qbuf.rst > @@ -54,7 +54,7 @@ When the buffer is intended for output (``type`` is > or ``V4L2_BUF_TYPE_VBI_OUTPUT``) applications must also initialize the > ``bytesused``, ``field`` and ``timestamp`` fields, see :ref:`buffer` > for details. Applications must also set ``flags`` to 0. The > -``reserved2`` and ``reserved`` fields must be set to 0. When using the > +``reserved`` field must be set to 0. When using the > :ref:`multi-planar API `, the ``m.planes`` field must > contain a userspace pointer to a filled-in array of struct > :c:type:`v4l2_plane` and the ``length`` field must be set > @@ -118,6 +118,51 @@ immediately with an ``EAGAIN`` error code when no buffer > is available. > The struct :c:type:`v4l2_buffer` structure is specified in > :ref:`buffer`. > > +Explicit Synchronization > + > + > +Explicit Synchronization allows us to control the synchronization of > +shared buffers from userspace by passing fences to the kernel and/or > +receiving them from it. Fences passed to the kernel are named in-fences and > +the kernel should wait on them to signal before using the buffer, i.e., > queueing > +it to the driver. I would drop ", i.e., queueing it to the driver" On the other side, the kernel can create out-fences for the > +buffers it queues to the drivers. Out-fences signal when the driver is > +finished with buffer, i.e., the buffer is ready. The fences are represented > +as a file and passed as a file descriptor to userspace. > + > +The in-fences are communicated to the kernel at the ``VIDIOC_QBUF`` ioctl > +using the ``V4L2_BUF_FLAG_IN_FENCE`` buffer flag and the `fence_fd` field. If > +an in-fence needs to be passed to the kernel, `fence_fd` should be set to the > +fence file descriptor number and the ``V4L2_BUF_FLAG_IN_FENCE`` should be set > +as well. Setting one but not the other will cause ``VIDIOC_QBUF`` to return > +with error. The fence_fd field will be ignored if the with -> with an > +``V4L2_BUF_FLAG_IN_FENCE`` is not set. > + > +The videobuf2-core will guarantee that all buffers queued with in-fence will with -> with an > +be queued to the drivers in the same order. Fence may signal out of order, so Fence -> Fences > +this guarantee at videobuf2 is necessary to not change ordering. Add some text here to make it clear that waiting for a buffer with an in-fence will also block all buffers queued after that buffer. > + > +If the in-fence signals with an error the videobuf2 won't queue the buffer to > +the driver, instead it will flag it with an error. And then wait for the > +previous buffer to complete before asking userspace dequeue the buffer with > +error - to make sure we deliver the buffers back in the correct order. I think there is no need to describe the internal implementation. It is enough to say that the buffer is marked with FLAG_ERROR if the in-fence signals an error. > + > +To get an out-fence back from V4L2 the ``V4L2_BUF_FLAG_OUT_FENCE`` flag > should > +be set to ask for a fence to be attached to the buffer. The out-fence fd is > +sent to userspace as a ``VIDIOC_QBUF`` return argument on the `fence_fd` > field. > + > +Note the the same `fence_fd` field is used for both sending the in-fence as > +input argument to receive the out-fence as a return argument. > + > +At streamoff the out-fences will either signal normally if the driver waits > +for the operations on the buffers to finish or signal with an error if the > +driver cancels the pending operations. Buffers with in-fences won't be queued > +to the driver if their fences signal. It will be cleaned up. It -> They It should be clarified here if you can or cannot use both in and out fences for the same buffer. > + > +The ``V4L2_FMT_FLAG_UNORDERED`` flag in ``VIDIOC_ENUM_FMT`` tells userspace > +that the current buffer queues is able to keep the ordering of
[PATCH v7 6/6] [media] v4l: Document explicit synchronization behavior
From: Gustavo PadovanAdd section to VIDIOC_QBUF about it v5: - Remove V4L2_CAP_ORDERED - Add doc about V4L2_FMT_FLAG_UNORDERED v4: - Document ordering behavior for in-fences - Document V4L2_CAP_ORDERED capability - Remove doc about OUT_FENCE event - Document immediate return of out-fence in QBUF v3: - make the out_fence refer to the current buffer (Hans) - Note what happens when the IN_FENCE is not set (Hans) v2: - mention that fences are files (Hans) - rework for the new API Signed-off-by: Gustavo Padovan --- Documentation/media/uapi/v4l/vidioc-qbuf.rst | 47 +++- Documentation/media/uapi/v4l/vidioc-querybuf.rst | 9 - 2 files changed, 54 insertions(+), 2 deletions(-) diff --git a/Documentation/media/uapi/v4l/vidioc-qbuf.rst b/Documentation/media/uapi/v4l/vidioc-qbuf.rst index 9e448a4aa3aa..8809397fb110 100644 --- a/Documentation/media/uapi/v4l/vidioc-qbuf.rst +++ b/Documentation/media/uapi/v4l/vidioc-qbuf.rst @@ -54,7 +54,7 @@ When the buffer is intended for output (``type`` is or ``V4L2_BUF_TYPE_VBI_OUTPUT``) applications must also initialize the ``bytesused``, ``field`` and ``timestamp`` fields, see :ref:`buffer` for details. Applications must also set ``flags`` to 0. The -``reserved2`` and ``reserved`` fields must be set to 0. When using the +``reserved`` field must be set to 0. When using the :ref:`multi-planar API `, the ``m.planes`` field must contain a userspace pointer to a filled-in array of struct :c:type:`v4l2_plane` and the ``length`` field must be set @@ -118,6 +118,51 @@ immediately with an ``EAGAIN`` error code when no buffer is available. The struct :c:type:`v4l2_buffer` structure is specified in :ref:`buffer`. +Explicit Synchronization + + +Explicit Synchronization allows us to control the synchronization of +shared buffers from userspace by passing fences to the kernel and/or +receiving them from it. Fences passed to the kernel are named in-fences and +the kernel should wait on them to signal before using the buffer, i.e., queueing +it to the driver. On the other side, the kernel can create out-fences for the +buffers it queues to the drivers. Out-fences signal when the driver is +finished with buffer, i.e., the buffer is ready. The fences are represented +as a file and passed as a file descriptor to userspace. + +The in-fences are communicated to the kernel at the ``VIDIOC_QBUF`` ioctl +using the ``V4L2_BUF_FLAG_IN_FENCE`` buffer flag and the `fence_fd` field. If +an in-fence needs to be passed to the kernel, `fence_fd` should be set to the +fence file descriptor number and the ``V4L2_BUF_FLAG_IN_FENCE`` should be set +as well. Setting one but not the other will cause ``VIDIOC_QBUF`` to return +with error. The fence_fd field will be ignored if the +``V4L2_BUF_FLAG_IN_FENCE`` is not set. + +The videobuf2-core will guarantee that all buffers queued with in-fence will +be queued to the drivers in the same order. Fence may signal out of order, so +this guarantee at videobuf2 is necessary to not change ordering. + +If the in-fence signals with an error the videobuf2 won't queue the buffer to +the driver, instead it will flag it with an error. And then wait for the +previous buffer to complete before asking userspace dequeue the buffer with +error - to make sure we deliver the buffers back in the correct order. + +To get an out-fence back from V4L2 the ``V4L2_BUF_FLAG_OUT_FENCE`` flag should +be set to ask for a fence to be attached to the buffer. The out-fence fd is +sent to userspace as a ``VIDIOC_QBUF`` return argument on the `fence_fd` field. + +Note the the same `fence_fd` field is used for both sending the in-fence as +input argument to receive the out-fence as a return argument. + +At streamoff the out-fences will either signal normally if the driver waits +for the operations on the buffers to finish or signal with an error if the +driver cancels the pending operations. Buffers with in-fences won't be queued +to the driver if their fences signal. It will be cleaned up. + +The ``V4L2_FMT_FLAG_UNORDERED`` flag in ``VIDIOC_ENUM_FMT`` tells userspace +that the current buffer queues is able to keep the ordering of buffers, i.e., +the dequeing of buffers will happen at the same order we queue them, with no +reordering by the driver. Return Value diff --git a/Documentation/media/uapi/v4l/vidioc-querybuf.rst b/Documentation/media/uapi/v4l/vidioc-querybuf.rst index dd54747fabc9..df964c4d916b 100644 --- a/Documentation/media/uapi/v4l/vidioc-querybuf.rst +++ b/Documentation/media/uapi/v4l/vidioc-querybuf.rst @@ -44,7 +44,7 @@ and the ``index`` field. Valid index numbers range from zero to the number of buffers allocated with :ref:`VIDIOC_REQBUFS` (struct :c:type:`v4l2_requestbuffers` ``count``) minus -one. The ``reserved`` and ``reserved2`` fields must be
[PATCH v7 6/6] [media] v4l: Document explicit synchronization behavior
From: Gustavo Padovan Add section to VIDIOC_QBUF about it v5: - Remove V4L2_CAP_ORDERED - Add doc about V4L2_FMT_FLAG_UNORDERED v4: - Document ordering behavior for in-fences - Document V4L2_CAP_ORDERED capability - Remove doc about OUT_FENCE event - Document immediate return of out-fence in QBUF v3: - make the out_fence refer to the current buffer (Hans) - Note what happens when the IN_FENCE is not set (Hans) v2: - mention that fences are files (Hans) - rework for the new API Signed-off-by: Gustavo Padovan --- Documentation/media/uapi/v4l/vidioc-qbuf.rst | 47 +++- Documentation/media/uapi/v4l/vidioc-querybuf.rst | 9 - 2 files changed, 54 insertions(+), 2 deletions(-) diff --git a/Documentation/media/uapi/v4l/vidioc-qbuf.rst b/Documentation/media/uapi/v4l/vidioc-qbuf.rst index 9e448a4aa3aa..8809397fb110 100644 --- a/Documentation/media/uapi/v4l/vidioc-qbuf.rst +++ b/Documentation/media/uapi/v4l/vidioc-qbuf.rst @@ -54,7 +54,7 @@ When the buffer is intended for output (``type`` is or ``V4L2_BUF_TYPE_VBI_OUTPUT``) applications must also initialize the ``bytesused``, ``field`` and ``timestamp`` fields, see :ref:`buffer` for details. Applications must also set ``flags`` to 0. The -``reserved2`` and ``reserved`` fields must be set to 0. When using the +``reserved`` field must be set to 0. When using the :ref:`multi-planar API `, the ``m.planes`` field must contain a userspace pointer to a filled-in array of struct :c:type:`v4l2_plane` and the ``length`` field must be set @@ -118,6 +118,51 @@ immediately with an ``EAGAIN`` error code when no buffer is available. The struct :c:type:`v4l2_buffer` structure is specified in :ref:`buffer`. +Explicit Synchronization + + +Explicit Synchronization allows us to control the synchronization of +shared buffers from userspace by passing fences to the kernel and/or +receiving them from it. Fences passed to the kernel are named in-fences and +the kernel should wait on them to signal before using the buffer, i.e., queueing +it to the driver. On the other side, the kernel can create out-fences for the +buffers it queues to the drivers. Out-fences signal when the driver is +finished with buffer, i.e., the buffer is ready. The fences are represented +as a file and passed as a file descriptor to userspace. + +The in-fences are communicated to the kernel at the ``VIDIOC_QBUF`` ioctl +using the ``V4L2_BUF_FLAG_IN_FENCE`` buffer flag and the `fence_fd` field. If +an in-fence needs to be passed to the kernel, `fence_fd` should be set to the +fence file descriptor number and the ``V4L2_BUF_FLAG_IN_FENCE`` should be set +as well. Setting one but not the other will cause ``VIDIOC_QBUF`` to return +with error. The fence_fd field will be ignored if the +``V4L2_BUF_FLAG_IN_FENCE`` is not set. + +The videobuf2-core will guarantee that all buffers queued with in-fence will +be queued to the drivers in the same order. Fence may signal out of order, so +this guarantee at videobuf2 is necessary to not change ordering. + +If the in-fence signals with an error the videobuf2 won't queue the buffer to +the driver, instead it will flag it with an error. And then wait for the +previous buffer to complete before asking userspace dequeue the buffer with +error - to make sure we deliver the buffers back in the correct order. + +To get an out-fence back from V4L2 the ``V4L2_BUF_FLAG_OUT_FENCE`` flag should +be set to ask for a fence to be attached to the buffer. The out-fence fd is +sent to userspace as a ``VIDIOC_QBUF`` return argument on the `fence_fd` field. + +Note the the same `fence_fd` field is used for both sending the in-fence as +input argument to receive the out-fence as a return argument. + +At streamoff the out-fences will either signal normally if the driver waits +for the operations on the buffers to finish or signal with an error if the +driver cancels the pending operations. Buffers with in-fences won't be queued +to the driver if their fences signal. It will be cleaned up. + +The ``V4L2_FMT_FLAG_UNORDERED`` flag in ``VIDIOC_ENUM_FMT`` tells userspace +that the current buffer queues is able to keep the ordering of buffers, i.e., +the dequeing of buffers will happen at the same order we queue them, with no +reordering by the driver. Return Value diff --git a/Documentation/media/uapi/v4l/vidioc-querybuf.rst b/Documentation/media/uapi/v4l/vidioc-querybuf.rst index dd54747fabc9..df964c4d916b 100644 --- a/Documentation/media/uapi/v4l/vidioc-querybuf.rst +++ b/Documentation/media/uapi/v4l/vidioc-querybuf.rst @@ -44,7 +44,7 @@ and the ``index`` field. Valid index numbers range from zero to the number of buffers allocated with :ref:`VIDIOC_REQBUFS` (struct :c:type:`v4l2_requestbuffers` ``count``) minus -one. The ``reserved`` and ``reserved2`` fields must be set to 0. When +one. The ``reserved`` field must be set to 0.