linux-kernel - Re: [PATCH v2 18/19] Revert "fbdev: Prevent probing generic drivers if a FB is already registered"

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Message-ID: <4ae20b63-f452-fdb4-ced6-d4968a8d69f0@redhat.com>
Date:   Wed, 9 Feb 2022 01:19:26 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Cc:     Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        linux-fbdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Zack Rusin <zackr@...are.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Ilya Trukhanov <lahvuun@...il.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Peter Jones <pjones@...hat.com>
Subject: Re: [PATCH v2 18/19] Revert "fbdev: Prevent probing generic drivers
 if a FB is already registered"

On 2/8/22 22:08, Daniel Vetter wrote:
> This reverts commit fb561bf9abde49f7e00fdbf9ed2ccf2d86cac8ee.
> 
> With
> 
> commit 27599aacbaefcbf2af7b06b0029459bbf682000d
> Author: Thomas Zimmermann <tzimmermann@...e.de>
> Date:   Tue Jan 25 10:12:18 2022 +0100
> 
>     fbdev: Hot-unplug firmware fb devices on forced removal
> 
> this should be fixed properly and we can remove this somewhat hackish
> check here (e.g. this won't catch drm drivers if fbdev emulation isn't
> enabled).
>

Unfortunately this hack can't be reverted yet. Thomas' patch solves the issue
of platform devices matched with fbdev drivers to be properly unregistered if
a DRM driver attempts to remove all the conflicting framebuffers.

But the problem that fb561bf9abde ("fbdev: Prevent probing generic drivers if
a FB is already registered") worked around is different. It happens when the
DRM driver is probed before the {efi,simple}fb and other fbdev drivers, the
kicking out of conflicting framebuffers already happened and these drivers
will be allowed to probe even when a DRM driver is already present.

We need a clearer way to prevent it, but can't revert fb561bf9abde until that.

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat