[libcamera-devel] [PATCH v2 11/27] libcamera: v4l2_videodevice: Document plane handling in createBuffer()

[Jean-Michel Hautbois]

Hi Laurent,

On 06/09/2021 04:00, Laurent Pinchart wrote:
> The V4L2VideoDevice::createBuffer() calculates offsets manually when
> using a multi-planar pixel format and a single-planar V4L2 format. The
> process isn't trivial, document it.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/libcamera/v4l2_videodevice.cpp | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> index 1483181a0856..88535f5a07c7 100644
> --- a/src/libcamera/v4l2_videodevice.cpp
> +++ b/src/libcamera/v4l2_videodevice.cpp
> @@ -1334,10 +1334,19 @@ std::unique_ptr<FrameBuffer> V4L2VideoDevice::createBuffer(unsigned int index)
>  	}
>  
>  	/*
> +	 * If we have a multi-planar format with a V4L2 single-planar buffer,
> +	 * split the single V4L2 plane into multiple FrameBuffer planes by
> +	 * computing the offsets manually.
> +	 *
>  	 * The format info is not guaranteed to be valid, as there are no
>  	 * PixelFormatInfo for metadata formats, so check it first.
>  	 */
>  	if (formatInfo_->isValid() && formatInfo_->numPlanes() != numPlanes) {
> +		/*
> +		 * There's no valid situation where the number of colour planes
> +		 * differs from the number of V4L2 planes and the V4L2 buffer
> +		 * has more than one plane.
> +		 */
>  		ASSERT(numPlanes == 1u);
>  
>  		planes.resize(formatInfo_->numPlanes());
>