Re: [PATCH] MAINTAINERS: Add Helge as fbdev maintainer

[Thomas Zimmermann]

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@xxxxxxxxxx> 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@xxxxxxxxxxxxxx
>
> 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

Attachment: OpenPGP_signature
Description: OpenPGP digital signature