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

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Date:   Wed, 19 Jan 2022 12:28:38 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Helge Deller <deller@....de>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-fbdev@...r.kernel.org, Sven Schnelle <svens@...ckframe.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"

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.

So perhaps this regression is caused by something else?

thanks,

greg k-h