Hi Thomas,

On Mon, Apr 26, 2021 at 2:22 PM Thomas Zimmermann [off-list ref] wrote:

Am 20.04.21 um 11:27 schrieb Geert Uytterhoeven:

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On Tue, Apr 20, 2021 at 11:22 AM Gerd Hoffmann [off-list ref] wrote:

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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?

Not that complicated, unless you want to do it Good & Fast ;-)

https://en.wikipedia.org/wiki/Hold-And-Modify

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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