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/ (local)
Fixes: d391c5827107 ("drivers/firmware: move x86 Generic System Framebuffers support")
Reported-by: Ilya Trukhanov <redacted>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Vetter <redacted>
---

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