Re: [PATCH v4 0/9] drm: Support simple-framebuffer devices and firmware fbs

Thomas Zimmermann
2021-04-26T12:22:24Z

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Hi

Am 20.04.21 um 11:27 schrieb Geert Uytterhoeven:
> Hi Gerd,
>
> On Tue, Apr 20, 2021 at 11:22 AM Gerd Hoffmann <kraxel@redhat.com> wrote:
>>>>> Patches 4 to 8 add the simpledrm driver. It's build on simple DRM helpers
>>>>> and SHMEM. It supports 16-bit, 24-bit and 32-bit RGB framebuffers. During
>>>>
>>>> .... if support for 8-bit frame buffers would be added?
>>>
>>> Is that 8-bit greyscale or 8-bit indexed with 256 entry palette? Former
>>> shouldn't be a big thing, but the latter is only really supported by the
>>> overall drm ecosystem in theory. Most userspace assumes that xrgb8888
>>> works, and we keep that illusion up by emulating it in kernel for hw which
>>> just doesn't support it. But reformatting xrgb8888 to c8 is tricky at
>>> best.
>>
>> Well. cirrus converts xrgb8888 on the fly to rgb888 or rgb565
>> (depending on display resolution). We could pull off the same trick
>> here and convert to rgb332 (assuming we can program the palette with the
>> color cube needed for that). Wouldn't look pretty, but would probably
>> work better than expecting userspace know what color palettes are in
>> 2021 ...
>
> Yeah, I already had a similar idea for Amiga HAM ;-)

I vaguely remember that HAM mode uses some crazy format where pixel
colors depend in the values of their neighbors. (?) How complicated is
it to write a conversion from RGB to HAM?

Best regards
Thomas

>
> Gr{oetje,eeting}s,
>
> Geert
>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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