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

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Message-ID: <ebe9c076-e2a9-0cb7-eb6a-ae71c075975e@gmx.de>
Date:   Tue, 18 Jan 2022 09:20:43 +0100
From:   Helge Deller <deller@....de>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        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>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] MAINTAINERS: Add Helge as fbdev maintainer

On 1/18/22 07:29, Gerd Hoffmann wrote:
>> Please correct me if I'm wrong, but text-console emulation/scrolling on DRM is
>> currently unaccelerated and bound to Truecolour modes only,
>
> Yes.  Adding support for formats beside argb8888 to the drm fbcon
> emulation shouldn't be that much of a problem though.

Really? Assuming a graphic card which runs with only 256 colors framebuffer
is easily supported by DRM, and you can use fbcon without using lots of memcpy()?

> Acceleration is harder.  The scroll acceleration had issues nobody
> addressed for years, and on modern hardware it is simply not used, which
> is probably the reason nobody stepped up fixing things and it ended up
> being dropped.

The DRM layer doesn't use scroll acceleration.
More than 30 other existing fbdev drivers use it.

> Bringing it back is much more work than just reverting the commits removing it.

Reverting those commits have no effect on DRM's usage of fbcon.
But reverting those commits bring back scroll acceleration for all others.
I'm trying to find out which patches did apparently fixed such issues
for the REDRAW case. If you have a pointer it would be helpful.

> Also note that using a shadow framebuffer allows to decouple fbcon
> updates and scanout framebuffer updates.  Can be used to speed up
> things without depending on the 2d blitter.

Not on older hardware.

Helge