On Mon, Aug 12, 2019 at 8:06 PM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> 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:
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
it permitted for a driver supporting this flag to not implement
V4L2_DEC_CMD_STOP?
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?
>
> 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-cisco@xxxxxxxxx>
> Tested-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> ---
> 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
>
