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SubjectRe: [PATCH] MAINTAINERS: Add Helge as fbdev maintainer
From
Hi

Am 17.01.22 um 14:29 schrieb Geert Uytterhoeven:
> Hi Gerd,
>
> On Mon, Jan 17, 2022 at 1:57 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
>>> b) to include new drivers (for old hardware) if they arrive (probably happens rarely but there can be).
>>> I know of at least one driver which won't be able to support DRM....
>>
>> Hmm? I seriously doubt that. There is always the option to use a
>> shadow framebuffer, then convert from standard drm formats to whatever
>> esoteric pixel format your hardware expects.
>>
>> Been there, done that. Have a look at the cirrus driver. The physical
>> hardware was designed in the early 90-ies, almost 30 years ago. These
>> days it exists in virtual form only (qemu emulates it). Thanks to the
>> drm driver it runs wayland just fine even though it has a bunch of
>> constrains dictated by the hardware design.
>
> The Cirrus DRM driver supports TrueColor (RGB565/888 and ARGB8888)
> modes only. The Cirrus fbdev driver also supports mochrome and 256
> color modes.
>
> There exist some DRM drivers that do support DRM_FORMAT_C8, but none of
> the "tiny" ones do. Same for DRM_FORMAT_RGB{332,233}. Using a shadow
> frame buffer to convert from truecolor to 256 colors would be doable,
> but would give bad results. And what about less colors?
> Adding support for e.g. DRM_FORMAT_C4 is not straight-forward, as
> the DRM core assumes in many places that a pixel is at least 1 byte,
> and would crash otherwise (yes I tried). Other modes needed are
> DRM_FORMAT_Y4 and DRM_FORMAT_{BW,WB} (monochrome).

We export XRGB32 from each driver, because userspace expects it. But
that is not a hard requirement. Userspace can use any format. It's just
that no one seems to have any use cases so far, so no work has been
done. Think of XRGB32 as a fallback.

Personally, I'd much appreciate if userspace would support more of the
native formats and not rely on XRGB32.


> This not only to support "old" hardware, but also modern small OLED
> and e-ink displays.

There's a DRM driver for Repaper e-Ink displays. So it seems doable at
least.

Best regards
Thomas

>
> On the positive side: DRM would force e.g. the Amiga and Atari
> bitplane formats to become internal to the kernel driver, with the
> kernel driver converting from packed pixels to bitplanes. Hence
> userspace would no longer have to care about bitplanes.
>
>
> 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

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