Hi Helen, On Fri, Jul 17, 2020 at 1:55 PM Helen Koike <helen.koike@xxxxxxxxxxxxx> wrote: > > Hi, > > I'm sorry for taking too long to submit v4. > > It is not perfect, not all v4l2-compliance tests passes, but I'd like a review, > specially on the API and potential problems, so I can focus on improving implementation > and maybe drop the RFC tag for next version. > > Follow below what changed in v4 and some items I'd like to discuss: > > > * Ioctl to replace v4l2_pix_format > --------------------------------------------------------------------------------- > During last media summit, we agreed to create ioctls that replace the v4l2_pix_format > struct and leave the other structs in the v4l2_format union alone. > Thus I refactored the code to receive struct v4l2_ext_pix_format, and I renamed the > ioctls, so now we have: > > int ioctl(int fd, VIDIOC_G_EXT_FMT, struct v4l2_ext_pix_format *argp); > int ioctl(int fd, VIDIOC_S_EXT_FMT, struct v4l2_ext_pix_format *argp); > int ioctl(int fd, VIDIOC_TRY_EXT_FMT, struct v4l2_ext_pix_format *argp); > > The only valid types are V4L2_BUF_TYPE_VIDEO_CAPTURE and V4L2_BUF_TYPE_VIDEO_OUTPUT, > all the other types are invalid with this API. > > > * Modifiers > --------------------------------------------------------------------------------- > I understand that unifying DRM and V4L2 pixel formats is not possible, but I'd like > to unify the modifiers [1]. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/drm/drm_fourcc.h#n290 > > Should we use the DRM modifiers directly in the V4L2 API? > Or should we move this header to a common place and change the prefix? (which requires > us to sync with DRM community). > Or should we create a v4l2 header, defining V4L2_ prefixed macros mapping to DRM_ > macros? > > For now, patch 1/6 includes drm/drm_fourcc.h and it is using DRM_FORMAT_MOD_* > > As discussed before, It would be nice to have documentation describing DRM fourcc > equivalents (I'm not sure if someone started this already), listing the number of > planes per format. > > We should also document which pixelformats are valid for the EXT_API, since multiplanar > and tile versions like V4L2_PIX_FMT_NV12MT_16X16 (which seems equivalent to > DRM_FORMAT_MOD_SAMSUNG_16_16_TILE, and could have a more generic name) should be > replaced by a modifier. > > Regarding flags [2] field in struct v4l2_pix_format_mplane [3]: > The only defined flag is V4L2_PIX_FMT_FLAG_PREMUL_ALPHA, and it is only used by vsp1 driver. > Which I believe could be replaced by a modifier, to avoid another field that changes > pixel formats, so I removed it from the EXT API (we can always add it back later with > the reserved fields). > > [2] https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/pixfmt-reserved.html#format-flags > [3] https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/pixfmt-v4l2-mplane.html?highlight=v4l2_pix_format_mplane#c.v4l2_pix_format_mplane > > We also discussed to add a new ENUM_FMT_EXT ioctl to return all pixelformats + modifiers > combinations. I still didn't add it in this version, but I don't think it affects > what is in this RFC and it can be added later. > > > * Buffers/Plane offset > --------------------------------------------------------------------------------- > > My understanding is that inside a memory buffer we can have multiple planes in random > offsets. > I was comparing with the DRM API [4], where it can have the same dmabuf for multiple > planes in different offsets, and I started to think we could simplify our API, so > I took the liberty to do some more changes, please review struct v4l2_ext_plane in > this RFC. > > I removed the data_offset, since it is unused (See Laurent's RFC repurposing this > field [5]). And comparing to the DRM API, it seems to me we only need a single offset > field. > > We could also check about overlapping planes in a memory buffer, but this is complicated > if we use the same memory buffer with different v4l2_ext_buffer objects. We can also leave > to the driver to check situations that may cause HW errors. > > [4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/drm/drm_mode.h#n489 > [5] https://patchwork.linuxtv.org/patch/29177/ > > > * Multistream Channels > --------------------------------------------------------------------------------- > During last media summit, we discussed about adding a channel number to the API to > support multistreams. i.e, to have multiple queues through a single video node. > > Use cases: > > - Blitters: can take multiple streams as input, which would require multiple OUTPUT queues. > > As Nicolas was explaining me: > "The blitters comes with a lot of variation between hardware. Most blitters at > least support 3 frames buffer. 2 inputs and one output. The second input is usually > optional, as the output buffer data is not always overwritten (e.g. SRC_OVER > blend or 1 input). Some of them have additional solid color or pattern that can > be used too. Advanced blitters will have composition feature, and may support more > input buffers to reduce the added latency that would be normally done through cascading > the operations. Note that each input can have different size and different cropping > region. Many blitters can scale and render to a sub-region of the CAPTURE buffer." > > - Multis-calers: can produce multiple streams, which would require multiple CAPTURE queues. > > As Nicolas was explaining me: > "This type of HW (or soft IP) is commonly found on HW used to produce internet > streams for fragmented and scalable protocols (HLS, DASH). Basically they are > used to transform one stream into multiple sized streams prior from being encoded." > > Modeling as channels allows the API to have synchronized Start/Stop between queues, > and also avoid the complexity of using the Media API in a topology with multiple video > nodes, which complicates userspace. > > This requires adding a new channel id in ioctls for formats (G_FMT/S_FMT/TRY_FMT), and > also for buffers (QBUF/DBUF). > We also need a mechanism to enumerate channels and their properties. > Since we don't have a clear view how this would work, for now I'm leaving reserved bits > in the structs, so we can add them later. > > > * Timecode > --------------------------------------------------------------------------------- > During last media summit, we discussed to return the v4l2_timecode field to the API, > since Nicolas mentioned that, even if it is not used by any upstreamed driver, it > is used by out-of-tree drivers. > > I've been discussing with Nicolas about this, and we can avoid adding too many metadata > to the buffer struct by using the Read-Only Request API [6] for retrieving more information > when required, similar to HDR. > > The RO Request API has the ability to read a control using a request that has already > completed, the control value lives as long as the request object. If it's not read > (or if there was no request), the data is simply ignored/discard. > > Since no upstream driver uses the timecode field, there are no conversions that need > to be done. > > [6] https://patchwork.kernel.org/cover/11635927/ > > > * Other changes (and some questions) in this version: > --------------------------------------------------------------------------------- > - Added reserved fields to struct > > - The only difference between previously proposed VIDIOC_EXT_EXPBUF and VIDIOC_EXPBUF, > was that with VIDIOC_EXT_EXPBUF we can export multiple planes at once. I think we > can add this later, so I removed it from this RFC to simplify it. > > - v4l2_buffer [7] has a memory field (enum v4l2_memory [8]). We kept this field in > struct v4l2_ext_buffer, buf I was wondering if this shouldn't be in struct v4l2_ext_plane > instead. > > [7] https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/buffer.html?highlight=v4l2_buffer#c.v4l2_buffer > [8] https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/buffer.html?highlight=v4l2_memory#c.v4l2_memory > > - In struct v4l2_ext_pix_format, we have: > > struct v4l2_plane_ext_pix_format plane_fmt[VIDEO_MAX_PLANES]; > > The number of planes can be deducted from plane_fmt[i].sizeimage != 0, so I removed > the num_planes field. Please let me know if we can't use sizeimage for this. > In DRM, we know the number of planes from drm_mode_fb_cmd2 by the number of handle > args passed which are not 0. > This also avoids num_planes to be bigger then VIDEO_MAX_PLANES. > > - Added flags field to struct v4l2_ext_create_buffers > > > * Fixed bugs here and there > --------------------------------------------------------------------------------- > I fixed some bugs found with v4l2-compliance (not all of them yet), > through script v4l-utils/contrib/test/test-media. > > I adapted what Boris did for v4l-utils in previous version to this version: > https://gitlab.collabora.com/koike/v4l-utils/-/tree/ext-api/wip > > Boris' questions regarding DMABUF in last version still holds [9]. > > [9] https://patchwork.linuxtv.org/project/linux-media/cover/20191008091119.7294-1-boris.brezillon@xxxxxxxxxxxxx/ > > > Please, let me know your feedback, > Helen > > > Boris Brezillon (5): > media: v4l2: Extend pixel formats to unify single/multi-planar > handling (and more) > media: videobuf2: Expose helpers to implement the _ext_fmt and > _ext_buf hooks > media: mediabus: Add helpers to convert a ext_pix format to/from a > mbus_fmt > media: vivid: Convert the capture and output drivers to > EXT_FMT/EXT_BUF > media: vimc: Implement the ext_fmt and ext_buf hooks > > Hans Verkuil (1): > media: v4l2: Add extended buffer operations > > .../media/common/videobuf2/videobuf2-core.c | 2 + > .../media/common/videobuf2/videobuf2-v4l2.c | 549 +++++----- > .../media/test-drivers/vimc/vimc-capture.c | 61 +- > drivers/media/test-drivers/vimc/vimc-common.c | 6 +- > drivers/media/test-drivers/vimc/vimc-common.h | 2 +- > drivers/media/test-drivers/vivid/vivid-core.c | 70 +- > .../test-drivers/vivid/vivid-touch-cap.c | 26 +- > .../test-drivers/vivid/vivid-touch-cap.h | 3 +- > .../media/test-drivers/vivid/vivid-vid-cap.c | 169 +--- > .../media/test-drivers/vivid/vivid-vid-cap.h | 15 +- > .../media/test-drivers/vivid/vivid-vid-out.c | 193 ++-- > .../media/test-drivers/vivid/vivid-vid-out.h | 15 +- > drivers/media/v4l2-core/v4l2-dev.c | 50 +- > drivers/media/v4l2-core/v4l2-ioctl.c | 934 ++++++++++++++++-- > include/media/v4l2-ioctl.h | 60 ++ > include/media/v4l2-mediabus.h | 42 + > include/media/videobuf2-core.h | 6 +- > include/media/videobuf2-v4l2.h | 21 +- > include/uapi/linux/videodev2.h | 144 +++ > 19 files changed, 1650 insertions(+), 718 deletions(-) I don't see any documentation being added by this series. I think it's been a long standing issue with this series and makes it difficult to review the UAPI itself, in separation from the kernel implementation details, which is especially important for any non-kernel developers willing to provide feedback. Best regards, Tomasz
