Re: [RFC 01/10] [media] vb2: add explicit fence user API

Philipp Zabel
2017-04-03T09:48:04Z

Hi Gustavo,

On Mon, 2017-03-13 at 16:20 -0300, Gustavo Padovan wrote:
> 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 return an out-fence from the kernel to
> userspace.
>
> Two new flags were added, V4L2_BUF_FLAG_IN_FENCE and
> V4L2_BUF_FLAG_OUT_FENCE. They should be used when setting in-fence and
> out-fence, respectively.
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
> ---
> drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 ++--
> drivers/media/v4l2-core/videobuf2-v4l2.c | 2 +-
> include/uapi/linux/videodev2.h | 6 ++++--
> 3 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> index eac9565..0a522cb 100644
> --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> @@ -348,7 +348,7 @@ struct v4l2_buffer32 {
> __s32 fd;
> } m;
> __u32 length;
> - __u32 reserved2;
> + __s32 fence_fd;
> __u32 reserved;
> };
>
> @@ -511,7 +511,7 @@ 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 3529849..d23c1bf 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 45184a2..3b6cfa6 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -911,7 +911,7 @@ struct v4l2_buffer {
> __s32 fd;
> } m;
> __u32 length;
> - __u32 reserved2;
> + __s32 fence_fd;
> __u32 reserved;
> };
>
> @@ -946,8 +946,10 @@ struct v4l2_buffer {
> #define V4L2_BUF_FLAG_TSTAMP_SRC_MASK 0x00070000
> #define V4L2_BUF_FLAG_TSTAMP_SRC_EOF 0x00000000
> #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE 0x00010000
> +#define V4L2_BUF_FLAG_IN_FENCE 0x00100000
> +#define V4L2_BUF_FLAG_OUT_FENCE 0x00200000
> /* mem2mem encoder/decoder */
> -#define V4L2_BUF_FLAG_LAST 0x00100000
> +#define V4L2_BUF_FLAG_LAST 0x00400000

This is not just a sentinel, it is a meaningful flag that must not be
changed. It indicates the last buffer produced by a hardware codec.

regards
Philipp