On 8/15/19 10:12 AM, Alexandre Courbot wrote:
> 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:
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.
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-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
>>
