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SubjectRe: [RFC v5 06/11] [media] vb2: add explicit fence user API
Em Fri, 17 Nov 2017 14:29:23 +0100
Hans Verkuil <hverkuil@xs4all.nl> escreveu:

> On 15/11/17 18:10, 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.
> >
> > 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.
>
> How would userspace know if fences are not supported? E.g. any driver that does
> not use vb2 will have no support for it.
>
> While the driver could clear the flag on return, the problem is that it is a bit
> late for applications to discover lack of fence support.
>
> Perhaps we do need a capability flag for this? I wonder what others think.

We're almost running out of flags at v4l2 caps (and at struct v4l2_buffer).

So, I would prefer to not add more flags on those structs if there is
another way.

As the fences out of order flags should go to ENUM_FMT (and, currently
there's just one flag defined there), I wander if it would make sense
to also add CAN_IN_FENCES/CAN_OUT_FENCES flags there, as maybe we
would want to disable/enable fences based on the format.

>
> Regards,
>
> Hans
>
> >
> >
> >
> > 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;
> > + __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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