Geert Uytterhoeven <ge...@linux-m68k.org> writes:
> Hi Marcus,
>
> On Tue, 29 Apr 2025 at 08:15, Marcus Folkesson
> <marcus.folkes...@gmail.com> wrote:
>> On Thu, Apr 24, 2025 at 10:38:33AM +0200, Geert Uytterhoeven wrote:
>>
>> [...]
>>
>> > > + /*
>> > > + * As the display supports grayscale, all pixels
>> > > must be written as two bits
>> > > + * even if the format is monochrome.
>> > > + *
>> > > + * The bit values maps to the following
>> > > grayscale:
>> > > + * 0 0 = White
>> > > + * 0 1 = Light gray
>> > > + * 1 0 = Dark gray
>> > > + * 1 1 = Black
>> >
>> > That is not R2, but D2?
>> > include/uapi/drm/drm_fourcc.h:
>> >
>> > /* 2 bpp Red (direct relationship between channel value and
>> > brightness) */
>> > #define DRM_FORMAT_R2 fourcc_code('R', '2', ' ', ' ')
>> > /* [7:0] R0:R1:R2:R3 2:2:2:2 four pixels/byte */
>> >
>> > /* 2 bpp Darkness (inverse relationship between channel value and
>> > brightness) */
>> > #define DRM_FORMAT_D2 fourcc_code('D', '2', ' ', ' ')
>> > /* [7:0] D0:D1:D2:D3 2:2:2:2 four pixels/byte */
>> >
>> > So the driver actually supports D1 and D2, and XRGB8888 should be
>> > inverted while converting to monochrome (and grayscale, which is not
>> > yet implemented).
>>
>> The display supports "reverse" grayscale, so the mapping becomes
>> 1 1 = White
>> 1 0 = Light gray
>> 0 1 = Dark gray
>> 0 0 = Black
>> instead.
>>
>> So I will probably add support for D1 and D2 formats and invert the
>> pixels for the R1, R2 and XRGB8888 formats.
>>
>> Could that work or are there any side effects that I should be aware of?
>
> That should work fine.
Agree.
> Note that you do not have to support R1 and R2, as they are non-native.
> AFAIK XRGB8888 is the only format all drivers must support.
>
> Gr{oetje,eeting}s,
>
That's correct. The driver should only support D1 and D2 as native formats
and (emulated) XRGB8888 for compatibility with existing user-space. No need
to support R1 and R2 since the controller does not support these formats.
--
Best regards,
Javier Martinez Canillas
Core Platforms
Red Hat
