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

[Thomas Zimmermann]

Hi

Am 17.01.22 um 15:47 schrieb Helge Deller:
> On 1/17/22 15:10, Geert Uytterhoeven wrote:
> [...]
> > Using an XRGB32 intermediate would kill the user experience on old
> > machines, due to both increased memory usage and copy overhead.
> >
> > > Personally, I'd much appreciate if userspace would support more of the
> > > native formats and not rely on XRGB32.
> >
> > Supporting monochrome, 16 colors, and 256 colors would be nice.
>
>  From this conversation it seems DRM completely lacks backwards compatibility,
> including a missing 2D bitblt copy.
> Isn't that all what's needed and then migrating existing drivers would
> be easy ?

What exactly do you mean by 'backwards compatibility'? The driver API is 
different, of course. My conversion helpers can provide a starting point 
to move fbdev code into DRM drivers.

For fbdev 2d-bitblt ioctls, you can add them to DRM drivers and set up 
DRM's fbdev emulation accordingly. Some DRM drivers do/did this. To my 
knowledge, so far there's not been a use case where that provides a 
benefit over simple memcpy. For fast 2d blitting from userspace, you 
should read Daniel's comment at [1]. tl;dr: a generic solution is 
non-trivial.

Best regards
Thomas

[1] https://blog.ffwll.ch/2018/08/no-2d-in-drm.html

> Helge
>
>
> > > > 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.
> >
> > Which uses an DRM_FORMAT_XRGB8888 intermediate, and
> > drm_fb_xrgb8888_to_gray8() and repaper_gray8_to_mono_reversed()
> > to convert from truecolor to monochrome.  I guess that would work,
> > as this is a slow e-ink display.  Have fun as a text console ;-)
> >
> > 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

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