All of
 help / color / mirror / Atom feed
From: Javier Martinez Canillas <>
To: Thomas Zimmermann <>,, "H . Peter Anvin" <>,
	Maarten Lankhorst <>,, Greg Kroah-Hartman <>,, Thomas Gleixner <>,
	Maxime Ripard <>,
	Borislav Petkov <>,
	Peter Robinson <>,
	Hans de Goede <>,, Ingo Molnar <>,
	David Airlie <>
Subject: Re: [RFC PATCH 0/4] Allow to use DRM fbdev emulation layer with CONFIG_FB disabled
Date: Wed, 1 Sep 2021 11:08:10 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <YS4iIR689bAZ4QT9@phenom.ffwll.local>

On 8/31/21 2:35 PM, Daniel Vetter wrote:
> On Sat, Aug 28, 2021 at 12:02:21AM +0200, Javier Martinez Canillas wrote:


>> We talked about a drmcon with Peter Robinson as well but then decided that a
>> way to disable CONFIG_FB but still having the DRM fbdev emulation could be a
>> intermediary step, hence these RFC patches.
>> But yes, I agree that a drmcon would be the proper approach for this, to not
>> need any fbdev support at all. We will just keep the explicit disable for the
>> fbdev drivers then in the meantime.
> I think the only intermediate step would be to disable the fbdev uapi
> (char node and anything in sysfs), while still registering against the
> fbcon layer so you have a console.

Right, $subject disabled the sysfs interface but left the fbdev chardev. I can
try to do a v2 that also disables that interface but just keep the fbcon part.
> But looking at the things syzbot finds the really problematic code is all
> in the fbcon and console layer in general, and /dev/fb0 seems pretty
> solid.

Yes, but still would be an improvement in the sense that no legacy fbdev uAPI
will be exposed and so user-space would only depend on the DRM/KMS interface.

> I think for a substantial improvement here in robustness what you really
> want is
> - kmscon in userspace
> - disable FB layer
> - ideally also disable console/vt layer in the kernel

Earlier in the thread it was mentioned that an in-kernel drmcon could be used
instead. My worry with kmscon is that moving something as critical as console
output to user-space might make harder to troubleshoot early booting issues.

And also that will require user-space changes. An in-kernel drmcon could be a
drop-in replacement though.

> - have a minimal emergency/boot-up log thing in drm, patches for that
>   floated around a few times

Interesting. Do you have any pointers for this? My search-fu failed me when
trying to find these patches.

Best regards,
Javier Martinez Canillas
Linux Engineering
Red Hat

  reply	other threads:[~2021-09-01  9:08 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-27 10:00 [RFC PATCH 0/4] Allow to use DRM fbdev emulation layer with CONFIG_FB disabled Javier Martinez Canillas
2021-08-27 10:00 ` [RFC PATCH 1/4] fbdev: Rename fb_*_device() functions names to match what they do Javier Martinez Canillas
2021-08-27 17:50 ` [RFC PATCH 0/4] Allow to use DRM fbdev emulation layer with CONFIG_FB disabled Thomas Zimmermann
2021-08-27 20:20   ` Daniel Vetter
2021-08-27 22:02     ` Javier Martinez Canillas
2021-08-31 12:35       ` Daniel Vetter
2021-09-01  9:08         ` Javier Martinez Canillas [this message]
2021-09-02 14:31           ` Daniel Vetter
2021-09-01 14:17         ` Sam Ravnborg
2021-09-09 15:52           ` Noralf Trønnes
2021-09-09 16:27             ` Noralf Trønnes
2021-09-10 16:05               ` Sam Ravnborg

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.