Re: [PATCH v7 3/6] [media] vb2: add explicit fence user API

Hans Verkuil
2018-01-12T12:20:21Z

On 01/10/18 17:07, 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 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.
>
> 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 | 15 +++++++++++++++
> drivers/media/common/videobuf/videobuf2-v4l2.c | 2 +-
> drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 ++--
> include/uapi/linux/videodev2.h | 7 ++++++-
> 4 files changed, 24 insertions(+), 4 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.

I'd also add: "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."

Regards,

Hans

> +
> + * .. _`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/common/videobuf/videobuf2-v4l2.c b/drivers/media/common/videobuf/videobuf2-v4l2.c
> index fac3cd6f901d..d838524a459e 100644
> --- a/drivers/media/common/videobuf/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf/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 = 0;
> b->reserved = 0;
>
> if (q->is_multiplanar) {
> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> index e48d59046086..a11a0a2bed47 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/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 58894cfe9479..2d424aebdd1e 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -933,7 +933,10 @@ struct v4l2_buffer {
> __s32 fd;
> } m;
> __u32 length;
> - __u32 reserved2;
> + union {
> + __s32 fence_fd;
> + __u32 reserved2;
> + };
> __u32 reserved;
> };
>
> @@ -970,6 +973,8 @@ 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
>