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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: 10+ 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
     [not found] <YS+Lhz9gg/>
2021-09-09 15:52 ` Noralf Trønnes
2021-09-09 16:27   ` Noralf Trønnes

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