linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Javier Martinez Canillas <javierm@redhat.com>
To: Thomas Zimmermann <tzimmermann@suse.de>,
	linux-kernel@vger.kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	x86@kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-fbdev@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	Maxime Ripard <mripard@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	Peter Robinson <pbrobinson@gmail.com>,
	Hans de Goede <hdegoede@redhat.com>,
	dri-devel@lists.freedesktop.org, Ingo Molnar <mingo@redhat.com>,
	David Airlie <airlied@linux.ie>
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: <b6ba8f6b-4f0c-53cc-e384-ecea3af78410@redhat.com> (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:

[snip]

>>
>> 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/0Caa+0@ravnborg.org>
2021-09-09 15:52 ` Noralf Trønnes
2021-09-09 16:27   ` Noralf Trønnes

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:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

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

  git send-email \
    --in-reply-to=b6ba8f6b-4f0c-53cc-e384-ecea3af78410@redhat.com \
    --to=javierm@redhat.com \
    --cc=airlied@linux.ie \
    --cc=bp@alien8.de \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=hdegoede@redhat.com \
    --cc=hpa@zytor.com \
    --cc=linux-fbdev@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=maarten.lankhorst@linux.intel.com \
    --cc=mingo@redhat.com \
    --cc=mripard@kernel.org \
    --cc=pbrobinson@gmail.com \
    --cc=tglx@linutronix.de \
    --cc=tzimmermann@suse.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* 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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).