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

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Date:   Wed, 19 Jan 2022 14:01:44 +0100
From:   Sven Schnelle <svens@...ckframe.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Helge Deller <deller@....de>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-fbdev@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.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-devel@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
        Gerd Hoffmann <kraxel@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sam Ravnborg <sam@...nborg.org>, Claudio Suarez <cssk@...-c.es>
Subject: Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"

Hi Greg,

Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:

> On Wed, Jan 19, 2022 at 12:22:55PM +0100, Greg Kroah-Hartman wrote:
>> On Wed, Jan 19, 2022 at 12:08:39PM +0100, Helge Deller wrote:
>> > This reverts commit 39aead8373b3c20bb5965c024dfb51a94e526151.
>> > 
>> > Revert this patch.  This patch started to introduce the regression that
>> > all hardware acceleration of more than 35 existing fbdev drivers were
>> > bypassed and thus fbcon console output for those was dramatically slowed
>> > down by factor of 10 and more.
>> > 
>> > Reverting this commit has no impact on DRM, since none of the DRM drivers are
>> > tagged with the acceleration flags FBINFO_HWACCEL_COPYAREA,
>> > FBINFO_HWACCEL_FILLRECT or others.
>> > 
>> > Signed-off-by: Helge Deller <deller@....de>
>> > Cc: stable@...r.kernel.org # v5.16
>> 
>> Why just 5.16?  This commit came in on 5.11 and was backported to
>> 5.10.5.
>> 
>> As for "why", I think there was a number of private bugs that were
>> reported in this code, which is why it was removed.  I do not think it
>> can be safely added back in without addressing them first.  Let me go
>> dig through my email to see if I can find them...
>
> Ah, no, that was just the soft scrollback code I was thinking of, which
> was a different revert and is still gone, thankfully :)
>
> This one was just removed because Daniel noticed that only 3 drivers
> used this (nouveau, omapdrm, and gma600), so this shouldn't have caused
> any regressions in any other drivers like you are reporting here.

I'm counting more than 3 drivers using this. I think one of the reasons
why it was reverted was that no one is actively maintaining fbdev. With
Helge now volunteering i don't see a reason why it should stay reverted.
If there are issues coming up i'm pretty sure Helge would care, and i
would probably also take a look.

/Sven