From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jiri Slaby <jirislaby@kernel.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
nouveau@lists.freedesktop.org,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
DRI Development <dri-devel@lists.freedesktop.org>,
Peter Rosin <peda@axentia.se>,
George Kennedy <george.kennedy@oracle.com>,
Tomi Valkeinen <tomi.valkeinen@ti.com>,
Ben Skeggs <bskeggs@redhat.com>,
Daniel Vetter <daniel.vetter@intel.com>,
Nathan Chancellor <natechancellor@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Peilin Ye <yepeilin.cs@gmail.com>
Subject: Re: [PATCH] fbcon: Disable accelerated scrolling
Date: Wed, 28 Oct 2020 17:57:37 +0100 [thread overview]
Message-ID: <20201028165737.GB2792004@kroah.com> (raw)
In-Reply-To: <20201028160600.3752105-1-daniel.vetter@ffwll.ch>
On Wed, Oct 28, 2020 at 05:06:00PM +0100, Daniel Vetter wrote:
> 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
> user of this accel code (it's not exposed as uapi through ioctls),
> which means we could garbage collect fairly enormous amounts of code
> if we kill this.
>
> Plus because syzbot only runs on virtual hardware, and none of the
> drivers for that have acceleration, we'd remove a huge gap in testing.
> And there's no other even remotely comprehensive testing aside from
> syzbot.
>
> This patch here just disables the acceleration code by always
> redrawing when scrolling. The plan is that once this has been merged
> for well over a year in released kernels, we can start to go around
> and delete a lot of code.
>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Ben Skeggs <bskeggs@redhat.com>
> Cc: nouveau@lists.freedesktop.org
> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Jiri Slaby <jirislaby@kernel.org>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Peilin Ye <yepeilin.cs@gmail.com>
> Cc: George Kennedy <george.kennedy@oracle.com>
> Cc: Nathan Chancellor <natechancellor@gmail.com>
> Cc: Peter Rosin <peda@axentia.se>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
> drivers/video/fbdev/core/fbcon.c | 38 ++++++--------------------------
> 1 file changed, 7 insertions(+), 31 deletions(-)
Nice!
But I'm with Sam, delete early :)
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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next prev parent reply other threads:[~2020-10-28 16:56 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 16:06 [PATCH] fbcon: Disable accelerated scrolling Daniel Vetter
2020-10-28 16:45 ` Sam Ravnborg
2020-10-28 16:48 ` Daniel Vetter
2020-10-28 16:57 ` Greg Kroah-Hartman [this message]
2020-10-28 18:50 ` Sam Ravnborg
2020-10-28 19:57 ` Daniel Vetter
2020-10-28 19:02 ` Thomas Zimmermann
2020-10-28 19:55 ` Daniel Vetter
2020-10-29 8:07 ` Thomas Zimmermann
2020-10-29 5:42 ` Jiri Slaby
2020-10-29 10:14 [PATCH 1/3] " Daniel Vetter
2020-10-29 13:22 ` [PATCH] " Daniel Vetter
2020-10-30 8:30 ` Tomi Valkeinen
2020-10-30 8:52 ` Daniel Vetter
2020-10-31 10:27 ` Geert Uytterhoeven
2020-10-31 14:17 ` Daniel Vetter
2020-11-18 9:21 ` Geert Uytterhoeven
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