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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Thu, 7 Jan 2021 09:13:10 +0100
Message-ID: <CAMuHMdXRgam2zahPEGcw8+76Xm-0AO-Ci9-YmVa5JpTKVHphRw@mail.gmail.com>
Subject: Re: [PATCH 5.10 28/63] fbcon: Disable accelerated scrolling
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>,
        Tomi Valkeinen <tomi.valkeinen@ti.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Sam Ravnborg <sam@ravnborg.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ben Skeggs <bskeggs@redhat.com>,
        Nouveau Dev <nouveau@lists.freedesktop.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Peilin Ye <yepeilin.cs@gmail.com>,
        George Kennedy <george.kennedy@oracle.com>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Peter Rosin <peda@axentia.se>,
        Daniel Vetter <daniel.vetter@intel.com>
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On Mon, Jan 4, 2021 at 5:58 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> From: Daniel Vetter <daniel.vetter@ffwll.ch>
>
> commit 39aead8373b3c20bb5965c024dfb51a94e526151 upstream.
>
> So ever since syzbot discovered fbcon, we have solid proof that it's
> full of bugs. And often the solution is to just delete code and remove
> features, e.g.  50145474f6ef ("fbcon: remove soft scrollback code").
>
> Now the problem is that most modern-ish drivers really only treat
> fbcon as an dumb kernel console until userspace takes over, and Oops
> printer for some emergencies. Looking at drm drivers and the basic
> vesa/efi fbdev drivers shows that only 3 drivers support any kind of
> acceleration:
>
> - nouveau, seems to be enabled by default
> - omapdrm, when a DMM remapper exists using remapper rewriting for
>   y/xpanning
> - gma500, but that is getting deleted now for the GTT remapper trick,
>   and the accelerated copyarea never set the FBINFO_HWACCEL_COPYAREA
>   flag, so unused (and could be deleted already I think).
>
> No other driver supportes accelerated fbcon. And fbcon is the only

Note that there are 32 more drivers using acceleration under
drivers/video/fbdev/.

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