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SubjectRe: [RFC v5 06/11] [media] vb2: add explicit fence user API
Em Wed, 15 Nov 2017 15:10:52 -0200
Gustavo Padovan <gustavo@padovan.org> escreveu:

> 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 and 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 a fence to the kernel to be waited on, and
> V4L2_BUF_FLAG_OUT_FENCE, to ask the kernel to give back an out-fence.
>
> 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 | 15 +++++++++++++++
> drivers/media/usb/cpia2/cpia2_v4l.c | 2 +-
> drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 ++--
> drivers/media/v4l2-core/videobuf2-v4l2.c | 2 +-
> include/uapi/linux/videodev2.h | 7 ++++++-
> 5 files changed, 25 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
> index ae6ee73f151c..eeefbd2547e7 100644
> --- a/Documentation/media/uapi/v4l/buffer.rst
> +++ b/Documentation/media/uapi/v4l/buffer.rst
> @@ -648,6 +648,21 @@ 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 fence passed in ``fence_fd`` field. The buffer
> + won't be queued to the driver until the fence signals.
> +
> + * .. _`V4L2-BUF-FLAG-OUT-FENCE`:
> +
> + - ``V4L2_BUF_FLAG_OUT_FENCE``
> + - 0x00400000
> + - Request a fence to be attached to the buffer. The ``fence_fd``
> + field on
> + :ref:`VIDIOC_QBUF` is used as a return argument to send the out-fence
> + fd to userspace.
>
>
>
> diff --git a/drivers/media/usb/cpia2/cpia2_v4l.c b/drivers/media/usb/cpia2/cpia2_v4l.c
> index 3dedd83f0b19..6cde686bf44c 100644
> --- a/drivers/media/usb/cpia2/cpia2_v4l.c
> +++ b/drivers/media/usb/cpia2/cpia2_v4l.c
> @@ -948,7 +948,7 @@ static int cpia2_dqbuf(struct file *file, void *fh, struct v4l2_buffer *buf)
> buf->sequence = cam->buffers[buf->index].seq;
> buf->m.offset = cam->buffers[buf->index].data - cam->frame_buffer;
> buf->length = cam->frame_size;
> - buf->reserved2 = 0;
> + buf->fence_fd = -1;
> buf->reserved = 0;
> memset(&buf->timecode, 0, sizeof(buf->timecode));
>
> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> index 821f2aa299ae..3a31d318df2a 100644
> --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> @@ -370,7 +370,7 @@ struct v4l2_buffer32 {
> __s32 fd;
> } m;
> __u32 length;
> - __u32 reserved2;
> + __s32 fence_fd;
> __u32 reserved;
> };
>
> @@ -533,7 +533,7 @@ static int put_v4l2_buffer32(struct v4l2_buffer *kp, struct v4l2_buffer32 __user
> put_user(kp->timestamp.tv_usec, &up->timestamp.tv_usec) ||
> copy_to_user(&up->timecode, &kp->timecode, sizeof(struct v4l2_timecode)) ||
> put_user(kp->sequence, &up->sequence) ||
> - put_user(kp->reserved2, &up->reserved2) ||
> + put_user(kp->fence_fd, &up->fence_fd) ||
> put_user(kp->reserved, &up->reserved) ||
> put_user(kp->length, &up->length))
> return -EFAULT;
> diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
> index 0c0669976bdc..110fb45fef6f 100644
> --- a/drivers/media/v4l2-core/videobuf2-v4l2.c
> +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
> @@ -203,7 +203,7 @@ 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->fence_fd = -1;
> b->reserved = 0;
>
> if (q->is_multiplanar) {
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index cd6fc1387f47..311c3a331eda 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -925,7 +925,10 @@ struct v4l2_buffer {
> __s32 fd;
> } m;
> __u32 length;
> - __u32 reserved2;
> + union {
> + __s32 fence_fd;

You forgot to document the fence_fd at the uAPI book. In particular,
it should be noticed there that a non-positive value means no fence.

(as userspace should be setting reserved2 to zero, I'm assuming
that we'll likely not accept 0 here).

You should likely also remove the description from reserved2 at
Documentation/media/uapi/v4l/buffer.rst.


> + __u32 reserved2;
> + };
> __u32 reserved;
> };
>
> @@ -962,6 +965,8 @@ struct v4l2_buffer {
> #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE 0x00010000
> /* mem2mem encoder/decoder */
> #define V4L2_BUF_FLAG_LAST 0x00100000
> +#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


--
Thanks,
Mauro

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