[libcamera-devel] [RFC PATCH v2 3/5] libcamera: v4l2 device: Store buffer info in planes

[Vedant Paranjape]

Hello Gabby,

Thanks for your patch. This patch looks good to me.

On Mon, Aug 21, 2023 at 6:40 PM Gabby George <gabbymg94 at gmail.com> wrote:
>
> To perform a memory mapping using mmap, the MappedFrameBuffer class
> needs the plane offset and file descriptor information of the frame
> buffer's plane(s). This information is provided in the response to
> REQBUF, which happens during buffer allocation. Store the plane offset
> and file descriptor information in the buffer's plane at the time of
> allocation.
>
> Currently, there is a metadata buffer type (metadata format UVCH) that
> does not support exporting buffers using EXPBUF, so this should only
> be done if the buffer type is metadata capture.
>
> Signed-off-by: Gabby George <gabbymg94 at gmail.com>

Reviewed-by: Vedant Paranjape <vedantparanjape160201 at gmail.com>

> ---
>  src/libcamera/v4l2_videodevice.cpp | 31 +++++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> index a72ef64d..e57cb131 100644
> --- a/src/libcamera/v4l2_videodevice.cpp
> +++ b/src/libcamera/v4l2_videodevice.cpp
> @@ -1402,18 +1402,27 @@ std::unique_ptr<FrameBuffer> V4L2VideoDevice::createBuffer(unsigned int index)
>
>         std::vector<FrameBuffer::Plane> planes;
>         for (unsigned int nplane = 0; nplane < numPlanes; nplane++) {
> -               UniqueFD fd = exportDmabufFd(buf.index, nplane);
> -               if (!fd.isValid())
> -                       return nullptr;
> -
>                 FrameBuffer::Plane plane;
> -               plane.fd = SharedFD(std::move(fd));
> -               /*
> -                * V4L2 API doesn't provide dmabuf offset information of plane.
> -                * Set 0 as a placeholder offset.
> -                * \todo Set the right offset once V4L2 API provides a way.
> -                */
> -               plane.offset = 0;
> +
> +               if (buf.type == V4L2_BUF_TYPE_META_CAPTURE) {
> +                       /*
> +                        * Dmabuf fd is not exported for metadata, so store
> +                        * the offset from the querybuf call and this device's fd.
> +                        */
> +                       plane.fd = SharedFD(this->fd());
> +                       plane.offset = buf.m.offset;
> +               } else {
> +                       UniqueFD fd = exportDmabufFd(buf.index, nplane);
> +                       if (!fd.isValid())
> +                               return nullptr;
> +                       plane.fd = SharedFD(std::move(fd));
> +                       /*
> +                       * V4L2 API doesn't provide dmabuf offset information of plane.
> +                       * Set 0 as a placeholder offset.
> +                       * \todo Set the right offset once V4L2 API provides a way.
> +                       */
> +                       plane.offset = 0;
> +               }
>                 plane.length = multiPlanar ? buf.m.planes[nplane].length : buf.length;
>
>                 planes.push_back(std::move(plane));
> --
> 2.34.1
>