linux-kernel - Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"

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Date:   Wed, 19 Jan 2022 15:11:58 +0100
From:   Helge Deller <deller@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Sven Schnelle <svens@...ckframe.org>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Ilia Mirkin <imirkin@...m.mit.edu>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Pavel Machek <pavel@....cz>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Sam Ravnborg <sam@...nborg.org>, Claudio Suarez <cssk@...-c.es>
Subject: Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"

On 1/19/22 15:01, Linus Torvalds wrote:
> On Wed, Jan 19, 2022 at 2:29 PM Helge Deller <deller@....de> wrote:
>>
>>>>
>>>> Ah, no, that was just the soft scrollback code I was thinking of, which
>>
>> Right.
>> That was commit 973c096f6a85 and it was about vgacon, not fbcon.
>
> No, fbcon had some bug too, although I've paged out the details. See
> commit 50145474f6ef ("fbcon: remove soft scrollback code").

Yes, but those bugs didn't affected

> If I remember correctly (and it's entirely possible that I don't), the
> whole "softback_lines" logic had serious problems with resizing the
> console (or maybe changing the font size).

Right.
I'm not asking to revert any soft scrollback functions.

It's about if you allow to use the fbdev-drivers hardware acceleration
to move parts of the screen or if you are stuck to software memcpy() and
repainting instead.
None of the bug reports touched that part.

> There may have been some other bad interaction with
> foreground/background consoles too, I forget.

I think that is independend if you use hardware acceleration or not.

Helge