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

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Date:   Wed, 19 Jan 2022 12:22:55 +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 12:08:39PM +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...

thanks,

greg k-h