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

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Date:   Fri, 12 Nov 2021 17:12:20 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>,
        Peter Jones <pjones@...hat.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>,
        Ilya Trukhanov <lahvuun@...il.com>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v2] fbdev: Prevent probing generic drivers if a FB is
 already registered

On Thu, Nov 11, 2021 at 12:39:28PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Nov 11, 2021 at 12:11:20PM +0100, Javier Martinez Canillas wrote:
> > The efifb and simplefb drivers just render to a pre-allocated frame buffer
> > and rely on the display hardware being initialized before the kernel boots.
> > 
> > But if another driver already probed correctly and registered a fbdev, the
> > generic drivers shouldn't be probed since an actual driver for the display
> > hardware is already present.
> > 
> > This is more likely to occur after commit d391c5827107 ("drivers/firmware:
> > move x86 Generic System Framebuffers support") since the "efi-framebuffer"
> > and "simple-framebuffer" platform devices are registered at a later time.
> > 
> > Link: https://lore.kernel.org/r/20211110200253.rfudkt3edbd3nsyj@lahvuun/
> > Fixes: d391c5827107 ("drivers/firmware: move x86 Generic System Framebuffers support")
> > Reported-by: Ilya Trukhanov <lahvuun@...il.com>
> > Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> > Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> > ---
> > 
> > Changes in v2:
> > - Add a Link: tag with a reference to the bug report (Thorsten Leemhuis).
> > - Add a comment explaining why the probe fails earlier (Daniel Vetter).
> > - Add a Fixes: tag for stable to pick the fix (Daniel Vetter).
> 
> That does not mean that it will make it into the stable tree.  Please
> read:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.

Defacto your auto-picker is aggressive enough that just Fixes: is actually
good enough to get it into stable :-)

But yeah explicit cc: stable can't hurt.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch