On Thu, Aug 15, 2019 at 8:53 PM Hans Verkuil <hverkuil-ci...@xs4all.nl> wrote:
>
> On 8/15/19 10:12 AM, Alexandre Courbot wrote:
> > On Mon, Aug 12, 2019 at 8:06 PM Hans Verkuil <hverkuil-ci...@xs4all.nl>
> > wrote:
> >>
> >> This RFC patch adds support for the V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF
> >> flag.
> >> It also adds a new V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF capability
> >> and
> >> a v4l2_m2m_release_capture_buf() helper function.
> >>
> >> Drivers should set vb2_queue->subsystem_flags to
> >> VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF
> >> to indicate support for this flag.
> >>
> >> The device_run() function should look like this:
> >>
> >> if (v4l2_m2m_release_capture_buf(out_vb, cap_vb)) {
> >> v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
> >> v4l2_m2m_job_finish(...);
> >> return;
> >> }
> >> cap_vb->is_held = out_vb->flags & V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
> >>
> >> ...
> >>
> >> v4l2_m2m_buf_done(out_vb, VB2_BUF_STATE_DONE);
> >> if (!cap_vb->is_held) {
> >> v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
> >> v4l2_m2m_job_finish(...);
> >> }
> >>
> >> In order to handle the corner case where V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF
> >> is always set for the output buffer, and you reached the last frame (so no
> >> new output buffer will be queued with a new timestamp), the driver should
> >> implement support for the V4L2_DEC_CMD_STOP command, and that should do:
>
> V4L2_DEC_CMD_STOP should have been CMD_FLUSH. Sorry for the confusion.
>
> >
> > I wonder if "the driver must implement..." would not make things
> > easier: what about drivers that only support formats for which we have
> > an exact 1:1 mapping (like VP8)? Should they also implement it? What
>
> Such drivers do not need this and will not set
> V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF. If that cap is not set,
> then V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF will be ignored.
>
> > it permitted for a driver supporting this flag to not implement
> > V4L2_DEC_CMD_STOP?
>
> Drivers that support this flag must implement DEC_CMD_FLUSH.
>
> >
> > Leaving this as an option may complicate user-space quite a bit. Since
> > the implementation of V4L2_DEC_CMD_STOP does not seem too complicated,
> > how about making it mandatory for all stateless decoders?
>
> It's a good question: should we support DEC_CMD_FLUSH also for decoders
> that do not set V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF?
>
> It would be a NOP, but it might simplify applications.
Supporting it as a NOP (maybe even transparently) seems to be the most
portable and easiest to handle for user-space.
>
> That said, I think we can postpone a decision about that until we have
> more experience. It is easier to add support for this than to remove
> it later.
>
> Regards,
>
> Hans
>
> >
> >
> >>
> >> struct vb2_v4l2_buffer *out_vb = v4l2_m2m_last_src_buf(m2m_ctx);
> >> struct vb2_v4l2_buffer *cap_vb = v4l2_m2m_last_dst_buf(m2m_ctx);
> >>
> >> if (out_vb) {
> >> out_vb->flags &= ~V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
> >> } else if (cap_vb && cap_vb->is_held) {
> >> v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
> >> v4l2_m2m_job_finish(...);
> >> }
> >>
> >> At least, I think so. Comments on this are very welcome. We definitely
> >> need better support in v4l2-mem2mem.c for such situations (same for
> >> stateful codecs) since it's too complex for drivers to get right IMHO.
> >>
> >> Regards,
> >>
> >> Hans
> >>
> >> Signed-off-by: Hans Verkuil <hverkuil-ci...@xs4all.nl>
> >> Tested-by: Boris Brezillon <boris.brezil...@collabora.com>
> >> Reviewed-by: Boris Brezillon <boris.brezil...@collabora.com>
> >> ---
> >> Documentation/media/uapi/v4l/buffer.rst | 13 ++++++
> >> .../media/uapi/v4l/vidioc-reqbufs.rst | 6 +++
> >> .../media/common/videobuf2/videobuf2-v4l2.c | 8 +++-
> >> include/media/v4l2-mem2mem.h | 42 +++++++++++++++++++
> >> include/media/videobuf2-core.h | 3 ++
> >> include/media/videobuf2-v4l2.h | 5 +++
> >> include/uapi/linux/videodev2.h | 13 +++---
> >> 7 files changed, 84 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/Documentation/media/uapi/v4l/buffer.rst
> >> b/Documentation/media/uapi/v4l/buffer.rst
> >> index 1cbd9cde57f3..afb03906ead9 100644
> >> --- a/Documentation/media/uapi/v4l/buffer.rst
> >> +++ b/Documentation/media/uapi/v4l/buffer.rst
> >> @@ -607,6 +607,19 @@ Buffer Flags
> >> applications shall use this flag for output buffers if the data in
> >> this buffer has not been created by the CPU but by some
> >> DMA-capable unit, in which case caches have not been used.
> >> + * .. _`V4L2-BUF-FLAG-M2M-HOLD-CAPTURE-BUF`:
> >> +
> >> + - ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF``
> >> + - 0x00000200
> >> + - Only valid if ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF`` is
> >> + set. It is typically used with stateless decoders where multiple
> >> + output buffers each decode to a slice of the decoded frame.
> >> + Applications can set this flag when queueing the output buffer
> >> + to prevent the driver from dequeueing the capture buffer after
> >> + the output buffer has been decoded (i.e. the capture buffer is
> >> + 'held'). If the timestamp of this output buffer differs from that
> >> + of the previous output buffer, then that indicates the start of a
> >> + new frame and the previously held capture buffer is dequeued.
> >> * .. _`V4L2-BUF-FLAG-LAST`:
> >>
> >> - ``V4L2_BUF_FLAG_LAST``
> >> diff --git a/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> >> b/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> >> index d7faef10e39b..d0c643db477a 100644
> >> --- a/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> >> +++ b/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
> >> @@ -125,6 +125,7 @@ aborting or finishing any DMA in progress, an implicit
> >> .. _V4L2-BUF-CAP-SUPPORTS-DMABUF:
> >> .. _V4L2-BUF-CAP-SUPPORTS-REQUESTS:
> >> .. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS:
> >> +.. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF:
> >>
> >> .. cssclass:: longtable
> >>
> >> @@ -150,6 +151,11 @@ aborting or finishing any DMA in progress, an implicit
> >> - The kernel allows calling :ref:`VIDIOC_REQBUFS` while buffers are
> >> still
> >> mapped or exported via DMABUF. These orphaned buffers will be
> >> freed
> >> when they are unmapped or when the exported DMABUF fds are closed.
> >> + * - ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF``
> >> + - 0x00000020
> >> + - Only valid for stateless decoders. If set, then userspace can set
> >> the
> >> + ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag to hold off on
> >> returning the
> >> + capture buffer until the OUTPUT timestamp changes.
> >>
> >> Return Value
> >> ============
> >> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >> b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >> index 5a9ba3846f0a..699787f48f46 100644
> >> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >> @@ -50,7 +50,8 @@ module_param(debug, int, 0644);
> >> V4L2_BUF_FLAG_TIMESTAMP_MASK)
> >> /* Output buffer flags that should be passed on to the driver */
> >> #define V4L2_BUFFER_OUT_FLAGS (V4L2_BUF_FLAG_PFRAME |
> >> V4L2_BUF_FLAG_BFRAME | \
> >> - V4L2_BUF_FLAG_KEYFRAME |
> >> V4L2_BUF_FLAG_TIMECODE)
> >> + V4L2_BUF_FLAG_KEYFRAME |
> >> V4L2_BUF_FLAG_TIMECODE | \
> >> + V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF)
> >>
> >> /*
> >> * __verify_planes_array() - verify that the planes array passed in struct
> >> @@ -194,6 +195,7 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer
> >> *vb, struct v4l2_buffer *b
> >> }
> >> vbuf->sequence = 0;
> >> vbuf->request_fd = -1;
> >> + vbuf->is_held = false;
> >>
> >> if (V4L2_TYPE_IS_MULTIPLANAR(b->type)) {
> >> switch (b->memory) {
> >> @@ -321,6 +323,8 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer
> >> *vb, struct v4l2_buffer *b
> >> */
> >> vbuf->flags &= ~V4L2_BUF_FLAG_TIMECODE;
> >> vbuf->field = b->field;
> >> + if (!(q->subsystem_flags &
> >> VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF))
> >> + vbuf->flags &= ~V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
> >> } else {
> >> /* Zero any output buffer flags as this is a capture
> >> buffer */
> >> vbuf->flags &= ~V4L2_BUFFER_OUT_FLAGS;
> >> @@ -654,6 +658,8 @@ static void fill_buf_caps(struct vb2_queue *q, u32
> >> *caps)
> >> *caps |= V4L2_BUF_CAP_SUPPORTS_USERPTR;
> >> if (q->io_modes & VB2_DMABUF)
> >> *caps |= V4L2_BUF_CAP_SUPPORTS_DMABUF;
> >> + if (q->subsystem_flags & VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF)
> >> + *caps |= V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF;
> >> #ifdef CONFIG_MEDIA_CONTROLLER_REQUEST_API
> >> if (q->supports_requests)
> >> *caps |= V4L2_BUF_CAP_SUPPORTS_REQUESTS;
> >> diff --git a/include/media/v4l2-mem2mem.h b/include/media/v4l2-mem2mem.h
> >> index 0b9c3a287061..724858efded2 100644
> >> --- a/include/media/v4l2-mem2mem.h
> >> +++ b/include/media/v4l2-mem2mem.h
> >> @@ -644,6 +644,48 @@ void v4l2_m2m_buf_copy_metadata(const struct
> >> vb2_v4l2_buffer *out_vb,
> >> struct vb2_v4l2_buffer *cap_vb,
> >> bool copy_frame_flags);
> >>
> >> +/**
> >> + * v4l2_m2m_release_capture_buf() - check if the capture buffer should be
> >> + * released
> >> + *
> >> + * @out_vb: the output buffer
> >> + * @cap_vb: the capture buffer
> >> + *
> >> + * This helper function returns true if the current capture buffer should
> >> + * be released to vb2. This is the case if the output buffer specified
> >> that
> >> + * the capture buffer should be held (i.e. not returned to vb2) AND if the
> >> + * timestamp of the capture buffer differs from the output buffer
> >> timestamp.
> >> + *
> >> + * This helper is to be called at the start of the device_run callback:
> >> + *
> >> + * .. code-block:: c
> >> + *
> >> + * if (v4l2_m2m_release_capture_buf(out_vb, cap_vb)) {
> >> + * v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
> >> + * v4l2_m2m_job_finish(...);
> >> + * return;
> >> + * }
> >> + * cap_vb->is_held = out_vb->flags &
> >> V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
> >> + *
> >> + * ...
> >> + *
> >> + * v4l2_m2m_buf_done(out_vb, VB2_BUF_STATE_DONE);
> >> + * if (!cap_vb->is_held) {
> >> + * v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
> >> + * v4l2_m2m_job_finish(...);
> >> + * }
> >> + *
> >> + * This allows for multiple output buffers to be used to fill in a single
> >> + * capture buffer. This is typically used by stateless decoders where
> >> + * multiple e.g. H.264 slices contribute to a single decoded frame.
> >> + */
> >> +static inline bool v4l2_m2m_release_capture_buf(const struct
> >> vb2_v4l2_buffer *out_vb,
> >> + const struct
> >> vb2_v4l2_buffer *cap_vb)
> >> +{
> >> + return cap_vb->is_held && cap_vb->vb2_buf.copied_timestamp &&
> >> + out_vb->vb2_buf.timestamp != cap_vb->vb2_buf.timestamp;
> >> +}
> >> +
> >> /* v4l2 request helper */
> >>
> >> void v4l2_m2m_request_queue(struct media_request *req);
> >> diff --git a/include/media/videobuf2-core.h
> >> b/include/media/videobuf2-core.h
> >> index 640aabe69450..a2b2208b02da 100644
> >> --- a/include/media/videobuf2-core.h
> >> +++ b/include/media/videobuf2-core.h
> >> @@ -505,6 +505,8 @@ struct vb2_buf_ops {
> >> * @buf_ops: callbacks to deliver buffer information.
> >> * between user-space and kernel-space.
> >> * @drv_priv: driver private data.
> >> + * @subsystem_flags: Flags specific to the subsystem (V4L2/DVB/etc.). Not
> >> used
> >> + * by the vb2 core.
> >> * @buf_struct_size: size of the driver-specific buffer structure;
> >> * "0" indicates the driver doesn't want to use a custom
> >> buffer
> >> * structure type. for example, ``sizeof(struct
> >> vb2_v4l2_buffer)``
> >> @@ -571,6 +573,7 @@ struct vb2_queue {
> >> const struct vb2_buf_ops *buf_ops;
> >>
> >> void *drv_priv;
> >> + u32 subsystem_flags;
> >> unsigned int buf_struct_size;
> >> u32 timestamp_flags;
> >> gfp_t gfp_flags;
> >> diff --git a/include/media/videobuf2-v4l2.h
> >> b/include/media/videobuf2-v4l2.h
> >> index 8a10889dc2fd..13ab101864aa 100644
> >> --- a/include/media/videobuf2-v4l2.h
> >> +++ b/include/media/videobuf2-v4l2.h
> >> @@ -33,6 +33,7 @@
> >> * @timecode: frame timecode.
> >> * @sequence: sequence count of this frame.
> >> * @request_fd: the request_fd associated with this buffer
> >> + * @is_held: if true, then this buffer was held
> >> * @planes: plane information (userptr/fd, length, bytesused,
> >> data_offset).
> >> *
> >> * Should contain enough information to be able to cover all the fields
> >> @@ -46,9 +47,13 @@ struct vb2_v4l2_buffer {
> >> struct v4l2_timecode timecode;
> >> __u32 sequence;
> >> __s32 request_fd;
> >> + bool is_held;
> >> struct vb2_plane planes[VB2_MAX_PLANES];
> >> };
> >>
> >> +/* VB2 V4L2 flags as set in vb2_queue.subsystem_flags */
> >> +#define VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF (1 << 0)
> >> +
> >> /*
> >> * to_vb2_v4l2_buffer() - cast struct vb2_buffer * to struct
> >> vb2_v4l2_buffer *
> >> */
> >> diff --git a/include/uapi/linux/videodev2.h
> >> b/include/uapi/linux/videodev2.h
> >> index 530638dffd93..4fa9f543742d 100644
> >> --- a/include/uapi/linux/videodev2.h
> >> +++ b/include/uapi/linux/videodev2.h
> >> @@ -915,11 +915,12 @@ struct v4l2_requestbuffers {
> >> };
> >>
> >> /* capabilities for struct v4l2_requestbuffers and v4l2_create_buffers */
> >> -#define V4L2_BUF_CAP_SUPPORTS_MMAP (1 << 0)
> >> -#define V4L2_BUF_CAP_SUPPORTS_USERPTR (1 << 1)
> >> -#define V4L2_BUF_CAP_SUPPORTS_DMABUF (1 << 2)
> >> -#define V4L2_BUF_CAP_SUPPORTS_REQUESTS (1 << 3)
> >> -#define V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS (1 << 4)
> >> +#define V4L2_BUF_CAP_SUPPORTS_MMAP (1 << 0)
> >> +#define V4L2_BUF_CAP_SUPPORTS_USERPTR (1 << 1)
> >> +#define V4L2_BUF_CAP_SUPPORTS_DMABUF (1 << 2)
> >> +#define V4L2_BUF_CAP_SUPPORTS_REQUESTS (1 << 3)
> >> +#define V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS (1 << 4)
> >> +#define V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF (1 << 5)
> >>
> >> /**
> >> * struct v4l2_plane - plane info for multi-planar buffers
> >> @@ -1041,6 +1042,8 @@ static inline __u64 v4l2_timeval_to_ns(const struct
> >> timeval *tv)
> >> #define V4L2_BUF_FLAG_IN_REQUEST 0x00000080
> >> /* timecode field is valid */
> >> #define V4L2_BUF_FLAG_TIMECODE 0x00000100
> >> +/* Don't return the capture buffer until OUTPUT timestamp changes */
> >> +#define V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF 0x00000200
> >> /* Buffer is prepared for queuing */
> >> #define V4L2_BUF_FLAG_PREPARED 0x00000400
> >> /* Cache handling flags */
> >> --
> >> 2.20.1
> >>
>
