linux-kernel - Re: [PATCH] drm/fb-helper: Only reject FB changes if FB_MISC_USER

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Message-ID: <CAPj87rNUj4b7nMkqDBp-cB8unoFjBGU=juTK8eyKmkTADWHmhw@mail.gmail.com>
Date:   Thu, 16 Mar 2017 10:09:17 +0000
From:   Daniel Stone <daniel@...ishbar.org>
To:     Michel Dänzer <michel@...nzer.net>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/fb-helper: Only reject FB changes if
 FB_MISC_USER_EVENT is set

Hi,

On 16 March 2017 at 09:55, Michel Dänzer <michel@...nzer.net> wrote:
> Otherwise this can also prevent modesets e.g. for switching VTs.
>
> FB_MISC_USER_EVENT is set when the request originates from userspace,
> which is what we're interested in here according to the DRM_DEBUG
> output.
>
> Bugzilla: https://bugs.freedesktop.org/99841
> Fixes: 865afb11949e ("drm/fb-helper: reject any changes to the fbdev")
> Signed-off-by: Michel Dänzer <michel.daenzer@....com>
> ---
>
> I'm not entirely sure why the values can not match for a VT switch. If
> anybody thinks this just papers over the real issue, please speak up.

It happens for me in multi-head with different resolutions. A real
compositor will set native resolutions with separate framebuffers, and
then fbcon will try to set one buffer for both outputs. This works on
the output with the larger resolution, but the one with the smaller
resolution will fail due to [xy]res_virtual (IIRC) being different.

I'll test this out later today.

Cheers,
Daniel