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    Subject[PATCH v10 11/16] vb2: add explicit fence user API
    Date
    From: Gustavo Padovan <gustavo.padovan@collabora.com>

    Turn the reserved2 field into fence_fd that we will use to send
    an in-fence to the kernel or return an out-fence from the kernel to
    userspace.

    Two new flags were added, V4L2_BUF_FLAG_IN_FENCE, that should be used
    when sending an in-fence to the kernel to be waited on, and
    V4L2_BUF_FLAG_OUT_FENCE, to ask the kernel to give back an out-fence.

    v8: return -1 if new flags are set.
    v7: minor fixes on the Documentation (Hans Verkuil)

    v6: big improvement on doc (Hans Verkuil)

    v5: - keep using reserved2 field for cpia2
    - set fence_fd to 0 for now, for compat with userspace(Mauro)

    v4: make it a union with reserved2 and fence_fd (Hans Verkuil)

    v3: make the out_fence refer to the current buffer (Hans Verkuil)

    v2: add documentation

    Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
    ---
    Documentation/media/uapi/v4l/buffer.rst | 48 ++++++++++++++++++++++---
    drivers/media/common/videobuf2/videobuf2-v4l2.c | 6 +++-
    drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 +--
    include/uapi/linux/videodev2.h | 8 ++++-
    4 files changed, 58 insertions(+), 8 deletions(-)

    diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
    index e2c85ddc990b..971b7453040c 100644
    --- a/Documentation/media/uapi/v4l/buffer.rst
    +++ b/Documentation/media/uapi/v4l/buffer.rst
    @@ -300,11 +300,23 @@ struct v4l2_buffer
    multi-planar API the application sets this to the number of
    elements in the ``planes`` array. The driver will fill in the
    actual number of valid elements in that array.
    - * - __u32
    - - ``reserved2``
    + * - __s32
    + - ``fence_fd``
    -
    - - A place holder for future extensions. Drivers and applications
    - must set this to 0.
    + - Used to communicate a fence file descriptor from userspace to kernel
    + and vice-versa. On :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` when sending
    + an in-fence for V4L2 to wait on, the ``V4L2_BUF_FLAG_IN_FENCE`` flag must
    + be used and this field set to the fence file descriptor of the in-fence.
    + If the in-fence is not valid ` VIDIOC_QBUF`` returns an error.
    +
    + To get an out-fence back from V4L2 the ``V4L2_BUF_FLAG_OUT_FENCE``
    + must be set, the kernel will return the out-fence file descriptor in
    + this field. If it fails to create the out-fence ``VIDIOC_QBUF` returns
    + an error.
    +
    + For all other ioctls V4L2 sets this field to -1 if
    + ``V4L2_BUF_FLAG_IN_FENCE`` and/or ``V4L2_BUF_FLAG_OUT_FENCE`` are set,
    + otherwise this field is set to 0 for backward compatibility.
    * - __u32
    - ``reserved``
    -
    @@ -648,6 +660,34 @@ Buffer Flags
    - Start Of Exposure. The buffer timestamp has been taken when the
    exposure of the frame has begun. This is only valid for the
    ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type.
    + * .. _`V4L2-BUF-FLAG-IN-FENCE`:
    +
    + - ``V4L2_BUF_FLAG_IN_FENCE``
    + - 0x00200000
    + - Ask V4L2 to wait on the fence passed in the ``fence_fd`` field. The
    + buffer won't be queued to the driver until the fence signals. The order
    + in which buffers are queued is guaranteed to be preserved, so any
    + buffers queued after this buffer will also be blocked until this fence
    + signals. This flag must be set before calling ``VIDIOC_QBUF``. For
    + other ioctls the driver just reports the value of the flag.
    +
    + If the fence signals the flag is cleared and not reported anymore.
    + If the fence is not valid ``VIDIOC_QBUF`` returns an error.
    + * .. _`V4L2-BUF-FLAG-OUT-FENCE`:
    +
    + - ``V4L2_BUF_FLAG_OUT_FENCE``
    + - 0x00400000
    + - Request for a fence to be attached to the buffer. The driver will fill
    + in the out-fence fd in the ``fence_fd`` field when :ref:`VIDIOC_QBUF
    + <VIDIOC_QBUF>` returns. This flag must be set before calling
    + ``VIDIOC_QBUF``. This flag is only an input, and is not set by the kernel.
    +
    + If the creation of the out-fence fails ``VIDIOC_QBUF`` returns an
    + error.
    +
    + Note that it is valid to set both ``V4L2_BUF_FLAG_IN_FENCE`` and
    + `V4L2_BUF_FLAG_OUT_FENCE`` flags. In such case, the ``fence_fd``
    + field is used to both set the in-fence and return the out-fence.



    diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
    index 64503615d00b..8312f61adfa6 100644
    --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
    +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
    @@ -203,9 +203,13 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
    b->timestamp = ns_to_timeval(vb->timestamp);
    b->timecode = vbuf->timecode;
    b->sequence = vbuf->sequence;
    - b->reserved2 = 0;
    b->reserved = 0;

    + if (b->flags & (V4L2_BUF_FLAG_IN_FENCE | V4L2_BUF_FLAG_OUT_FENCE))
    + b->fence_fd = -1;
    + else
    + b->fence_fd = 0;
    +
    if (q->is_multiplanar) {
    /*
    * Fill in plane-related data if userspace provided an array
    diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
    index 4312935f1dfc..93c752459aec 100644
    --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
    +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
    @@ -388,7 +388,7 @@ struct v4l2_buffer32 {
    __s32 fd;
    } m;
    __u32 length;
    - __u32 reserved2;
    + __s32 fence_fd;
    __u32 reserved;
    };

    @@ -606,7 +606,7 @@ static int put_v4l2_buffer32(struct v4l2_buffer __user *kp,
    assign_in_user(&up->timestamp.tv_usec, &kp->timestamp.tv_usec) ||
    copy_in_user(&up->timecode, &kp->timecode, sizeof(kp->timecode)) ||
    assign_in_user(&up->sequence, &kp->sequence) ||
    - assign_in_user(&up->reserved2, &kp->reserved2) ||
    + assign_in_user(&up->fence_fd, &kp->fence_fd) ||
    assign_in_user(&up->reserved, &kp->reserved) ||
    get_user(length, &kp->length) ||
    put_user(length, &up->length))
    diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
    index a8842a5ca636..1f18dc68ecab 100644
    --- a/include/uapi/linux/videodev2.h
    +++ b/include/uapi/linux/videodev2.h
    @@ -934,7 +934,10 @@ struct v4l2_buffer {
    __s32 fd;
    } m;
    __u32 length;
    - __u32 reserved2;
    + union {
    + __s32 fence_fd;
    + __u32 reserved2;
    + };
    __u32 reserved;
    };

    @@ -971,6 +974,9 @@ struct v4l2_buffer {
    #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE 0x00010000
    /* mem2mem encoder/decoder */
    #define V4L2_BUF_FLAG_LAST 0x00100000
    +/* Explicit synchronization */
    +#define V4L2_BUF_FLAG_IN_FENCE 0x00200000
    +#define V4L2_BUF_FLAG_OUT_FENCE 0x00400000

    /**
    * struct v4l2_exportbuffer - export of video buffer as DMABUF file descriptor
    --
    2.16.3
    \
     
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