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Date:   Wed, 19 Jan 2022 12:22:55 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Helge Deller <deller@gmx.de>
Cc:     Thomas Zimmermann <tzimmermann@suse.de>,
        linux-fbdev@vger.kernel.org, Sven Schnelle <svens@stackframe.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Ilia Mirkin <imirkin@alum.mit.edu>,
        Tomi Valkeinen <tomi.valkeinen@ti.com>,
        dri-devel@lists.freedesktop.org,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org,
        Gerd Hoffmann <kraxel@redhat.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Sam Ravnborg <sam@ravnborg.org>, Claudio Suarez <cssk@net-c.es>
Subject: Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"
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References: <20220119110839.33187-1-deller@gmx.de>
 <20220119110839.33187-3-deller@gmx.de>
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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@gmx.de>
> Cc: stable@vger.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...

thanks,

greg k-h