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

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Message-ID: <YY0A8LOVhs5JbMXW@kroah.com>
Date:   Thu, 11 Nov 2021 12:39:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     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 12:11:20PM +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.

thanks,

greg k-h