Re: [RFC v5 10/15] media: v4l: uapi: Add a control for colour pattern flipping effect

Sakari Ailus
2025-02-10T13:53:22Z

Hi Mirela,

On Sun, Feb 09, 2025 at 07:23:10PM +0200, Mirela Rabulea wrote:
> Hi Sakari,
>
> On 03.02.2025 10:58, Sakari Ailus wrote:
> > Add a bitmask control (V4L2_CID_COLOUR_PATTERN_FLIP) to tell whether
> > flipping results in a change in the sensor's colour pattern, separately
> > horizontally and vertically. The information is essential for raw formats
> > when using generic raw mbus codes.
>
> Is this control really necessary? Are there cases when V4L2_CID_HFLIP or/and
> V4L2_CID_VFLIP is enabled and the CFA pattern does not change?

Some sensors have some tricks in firmware to avoid changing the pattern (I
suppose in reality they crop one line / column) but this may not be
controllable by the driver, so this possibility should be taken into
account.

>
> Could a raw sensor driver be capable of reporting the
> V4L2_CID_COLOUR_PATTERN based on current values of the HFLIP/VFLIP? I'm not
> sure I understood all the aspects of patch #7 (V4L2_CID_COLOUR_PATTERN).

In principle it could. The two were originally made independent also
because there was an inconvenient dependency between mbus codes and
controls. If the pattern control does not specify the native pattern but an
active pattern (whatever has an effect on it), the userspace also must
check that configuration to determine the native pattern. My understanding
is the preference on that side is the native pattern.

--
Regards,

Sakari Ailus