Re: Reply cause of the image error in Gnome Snapshot [PATCH v3 0/3] media: Add support for the Sony IMX681

[Sergey Lebedev <lsa.uz@pm.me>]

Short, because the detail belongs on another list.

The colour errors and the lines German reported are not in the sensor
drivers. His control shows it: the same pipeline renders correctly when the
software ISP is forced onto the CPU.

  LIBCAMERA_SOFTISP_MODE=cpu qcam --stream "width=1920,height=1080"

Same kernel, same driver, same sensor, same resolution. Only the debayer
implementation changes.

It is a GPU debayer problem in libcamera, and it turns on the input stride
being larger than the width. I measured that side here. The IPU7 ISYS video
node rounds width up to a multiple of 32 pixels - fourteen widths, no
exceptions - and German's IMX681 figure reproduces exactly: width 3844 gives
a stride of 7744 bytes, which is 3872 pixels.

That padding is the ISYS node's. A sensor subdev has no bytesperline to set.
It is also ordinary V4L2: a driver may pad, and a consumer must use the
bytesperline it is handed.

So nothing in this thread asks for a change to the IMX681 series. I am
sending German the rest separately - the upstream patch this matches, what
the v0.7.2 source actually does, and where I would look next - so that it can
go to libcamera-devel, where it belongs and where I do not want to drag this
thread.

Sergey