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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 19 Jan 2022 12:47:50 +0100
Message-ID: <CAMuHMdVWFJEDwjf-htZ_D1484efmuPnz_L-qhcTeUE-GVpvZXA@mail.gmail.com>
Subject: Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Helge Deller <deller@gmx.de>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Linux Fbdev development list <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 Development <dri-devel@lists.freedesktop.org>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Pavel Machek <pavel@ucw.cz>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Sam Ravnborg <sam@ravnborg.org>, Claudio Suarez <cssk@net-c.es>
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Hi Greg,

On Wed, Jan 19, 2022 at 12:28 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> 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@gmx.de>

> > 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

So the bugs argument is moot.

> was a different revert and is still gone, thankfully :)

FTR, not everyone else was thankful about that one...

> 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?

1. Daniel's patch was not CCed to linux-fbdev,
2. When I discovered the patch, I pointed out that the premise of 3
   drivers was not true, and that it affects 32 more fbdev drivers[1] .
   The patch was applied regardless.
3. When the patch was suggested for backporting, I pointed out the
   same[2].
   The patch was backported regardless.

[1] https://lore.kernel.org/r/alpine.DEB.2.22.394.2010311116530.379363@ramsan.of.borg/
[2] https://lore.kernel.org/r/CAMuHMdXRgam2zahPEGcw8+76Xm-0AO-Ci9-YmVa5JpTKVHphRw@mail.gmail.com/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds