Hi Nicolas, On 3/23/22 16:05, Nicolas Dufresne wrote: > Hi Dmitry, > > thanks for giving a second look a this issue. > > Le mardi 22 mars 2022 à 16:23 +0300, Dmitry Osipenko a écrit : >> Use data offsets provided by applications for multi-planar capture >> buffers. This allows V4L to import and use dma-bufs exported by other >> subsystems in cases where application wants to customize data offsets >> of capture buffers in order to meet hardware alignment requirements of >> both dma-buf exporter and importer. >> >> This feature is wanted for providing a better support of media hardware >> found on Chromebooks. In particular display and camera ISP hardware of >> Rockchip and MediaTek SoCs require special handling by userspace because >> display h/w has specific alignment requirements that don't match default >> alignments expected by V4L and there is a need to customize the data >> offsets in case of multi-planar formats. >> >> Some drivers already have preliminary support for data offsets >> customization of capture buffers, like NVIDIA Tegra video decoder driver >> for example, and V4L allows applications to provide data offsets for >> multi-planar output buffers, let's support such customization for the >> capture buffers as well. >> >> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> >> --- >> Documentation/userspace-api/media/v4l/buffer.rst | 9 ++++++++- >> drivers/media/common/videobuf2/videobuf2-v4l2.c | 7 +++++++ >> 2 files changed, 15 insertions(+), 1 deletion(-) >> >> diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst >> index 4638ec64db00..75b1929e2acb 100644 >> --- a/Documentation/userspace-api/media/v4l/buffer.rst >> +++ b/Documentation/userspace-api/media/v4l/buffer.rst >> @@ -369,13 +369,20 @@ struct v4l2_plane >> - ``data_offset`` >> - Offset in bytes to video data in the plane. Drivers must set this >> field when ``type`` refers to a capture stream, applications when >> - it refers to an output stream. >> + it refers to an output or capture stream. > > There is a clear contradiction in this paragraph. Both the driver and the > application MUST set the data_offset. I'm not sure where the contradiction is. Application must initialize the data_offset and driver must set data_offset too, if it's appropriate to do that for a particular driver. > Would it be possible to demo your idea by implementing this in a virtual driver > ? vivid already have data_offset for capture in some cases, you could verify if > your idea works without any conflict in this scenario. I actually considered implementing it in the vivid driver, but vivid driver already sets the data_offset to fixed values [1], so I decided that not to change it. But maybe we actually could extend the vivid driver by accepting data_offset from userspace for the cases where the fixed offset value is zero in the driver.. not sure. [1] https://elixir.bootlin.com/linux/latest/source/drivers/media/test-drivers/vivid/vivid-vid-cap.c#L172 I verified my idea using the NVIDIA Tegra video decoder driver, which already takes data_offsets for capture planes [3] and libvdpau-tegra imports DRM dma-bufs into the V4L driver [4][5]. [3] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/media/platform/nvidia/tegra-vde/v4l2.c#n236 [4] https://github.com/grate-driver/libvdpau-tegra/blob/master/src/decoder.c#L685 [5] https://github.com/grate-driver/libvdpau-tegra/blob/master/src/v4l2.c#L359 The plan is to extend RK ISP driver with support of data_offsets next, once we'll agree that this acceptable approach and we don't actually need go back to implementing the new VIDIOC_EXT_QBUF ioctl [6]. [6] https://patchwork.linuxtv.org/project/linux-media/cover/20210114180738.1758707-1-helen.koike@xxxxxxxxxxxxx/ This patch solves the problem for userspace when it wants to import buffers into V4L in case of multi-planar formats, but it doesn't cover all other possible cases that may require offsets customization too. On the other hand, it's easy to start accepting data_offset for the capture MPLANES without introducing new UAPIs, so I decided that will be best to start easy with the simplest solution.
