linux-kernel - Re: [PATCH] MAINTAINERS: Add Helge as fbdev maintainer

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Date:   Mon, 24 Jan 2022 19:38:54 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Gerd Hoffmann <kraxel@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Helge Deller <deller@....de>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Sven Schnelle <svens@...ckframe.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] MAINTAINERS: Add Helge as fbdev maintainer

Hi Daniel,

On Fri, Jan 21, 2022 at 9:55 AM Daniel Vetter <daniel@...ll.ch> wrote:
> Just to clarify, since we had lots of smaller and bigger
> misunderstandings in the thread thus far: DRM_FORMAT_RGB332 exists, so
> drm support that already. The fbdev emulation doesn't yet, but all
> that's needed for that is filling out the code to remap the drm
> description to the fbdev format description for this case. Plus
> testing it all works ofc with fbcon and whatelse. Note that RGB332  is
> a bit more work than e.g. C4, since atm fbdev still uses only bpp to
> identify formats, so would need to be switch over to drm_fourcc first
> before adding anything which aliases with something existing (we have
> C8 already wired up).

I doubt that RGB332 would be a bit more work than C4, as RGB332 is still
8 bpp, while C4 is less.  To support C4, all DRM code that cannot
handle format->cpp[0] < 1 or drm_format_info_block_width() > 1 has to be
fixed first.

On the plus side, I finally got my proof-of-concept Atari DRM driver
working with fbcon on ARAnyM.  Mapping /dev/fb0 from userspace doesn't
work (fbtest SEGVs while reading from the mapped frame buffer).  I don't
know yet if this is a general issue without deferred I/O in v5.17-rc1,
or a bug in the m68k MM code...

So far it supports C8 only, but I hope to tackle C4 and monochrome soon.
Whether the end result will be usable on real hardware is still to be
seen, but at least I hope to get some DRM code written...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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