(fix copy and paste error in the cover letter) As was discussed here (among other places):
https://lkml.org/lkml/2018/10/19/440 using capture queue buffer indices to refer to reference frames is not a good idea. A better idea is to use a 'tag' where the application can assign a u32 tag to an output buffer, which is then copied to the capture buffer(s) derived from the output buffer. It has been suggested that the timestamp can be used for this. But there are a number of reasons why this is a bad idea: 1) the struct timeval is converted to a u64 in vb2. So there can be all sorts of unexpected conversion issues. In particular, the output of ns_to_timeval(timeval_to_ns(tv)) does not necessarily match the input. 2) it gets worse with the y2038 code where userspace either deals with a 32 bit tv_sec value or a 64 bit value. In other words, using timestamp for this is not a good idea. This implementation adds a new tag field in a union with the reserved2 field. The interpretation of that union depends on the flags field, so it still can be used for other things as well. In addition, in the previous patches the tag was in a union with the timecode field (again determined by the flags field), so if we need to cram additional information in this struct we can always put it in a union with the timecode field as well. It worked for the tag, it should work for other things. But we really need to start looking at a struct v4l2_ext_buffer. The first three patches add core tag support, the next two patches document the tag support, then a new helper function is added to v4l2-mem2mem.c to easily copy data from a source to a destination buffer that drivers can use. Next a new supports_tags vb2_queue flag is added to indicate that the driver supports tags. Ideally this should not be necessary, but that would require that all m2m drivers are converted to using the new helper function introduced in the previous patch. That takes more time then I have now. Finally the vim2m, vicodec and cedrus drivers are converted to support tags. I also removed the 'pad' fields from the mpeg2 control structs (it should never been added in the first place) and aligned the structs to a u32 boundary. Note that this might change further (Paul suggested using bitfields). Also note that the cedrus code doesn't set the sequence counter, that's something that should still be added before this driver can be moved out of staging. Note: if no buffer is found for a certain tag, then the dma address is just set to 0. That happened before as well with invalid buffer indices. This should be checked in the driver! Regards, Hans Changes since v3: - use reserved2 for the tag - split the documentation in two: one documenting the tag, one cleaning up the timecode documentation. Changes since v2: - rebased - added Reviewed-by tags - fixed a few remaining references in the documentation to the old v4l2_buffer_tag struct that was used in early versions of this series. Changes since v1: - changed to a u32 tag. Using a 64 bit tag was overly complicated due to the bad layout of the v4l2_buffer struct, and there is no real need for it by applications. Main changes since the RFC: - Added new buffer capability flag - Added m2m helper to copy data between buffers - Added documentation - Added tag logging in v4l2-ioctl.c Hans Verkuil (10): videodev2.h: add tag support vb2: add tag support v4l2-ioctl.c: log v4l2_buffer tag buffer.rst: document the new buffer tag feature. buffer.rst: clean up timecode documentation v4l2-mem2mem: add v4l2_m2m_buf_copy_data helper function vb2: add new supports_tags queue flag vim2m: add tag support vicodec: add tag support cedrus: add tag support Documentation/media/uapi/v4l/buffer.rst | 28 +++++++++---- .../media/uapi/v4l/vidioc-reqbufs.rst | 4 ++ .../media/common/videobuf2/videobuf2-v4l2.c | 41 ++++++++++++++++--- drivers/media/platform/vicodec/vicodec-core.c | 14 ++----- drivers/media/platform/vim2m.c | 14 ++----- drivers/media/v4l2-core/v4l2-ctrls.c | 9 ---- drivers/media/v4l2-core/v4l2-ioctl.c | 9 ++-- drivers/media/v4l2-core/v4l2-mem2mem.c | 23 +++++++++++ drivers/staging/media/sunxi/cedrus/cedrus.h | 9 ++-- .../staging/media/sunxi/cedrus/cedrus_dec.c | 2 + .../staging/media/sunxi/cedrus/cedrus_mpeg2.c | 21 ++++------ .../staging/media/sunxi/cedrus/cedrus_video.c | 2 + include/media/v4l2-mem2mem.h | 21 ++++++++++ include/media/videobuf2-core.h | 2 + include/media/videobuf2-v4l2.h | 21 +++++++++- include/uapi/linux/v4l2-controls.h | 14 +++---- include/uapi/linux/videodev2.h | 9 +++- 17 files changed, 168 insertions(+), 75 deletions(-) -- 2.19.1
