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SubjectRe: [PATCH] fbdev: wait for references go away
  Hi,

> > open. Which can result in drm driver not being able to grab resources
> > (and fail initialization) because the firmware framebuffer still holds
> > them. Reportedly plymouth can trigger this.
>
> Could you please describe issue some more?
>
> I guess that a problem is happening during DRM driver load while fbdev
> driver is loaded? I assume do_unregister_framebuffer() is called inside
> do_remove_conflicting_framebuffers()?

Yes. Specifically bochs-drm.ko and efifb in virtual machines.

> At first glance it seems to be an user-space issue as it should not be
> holding references on /dev/fb0 while DRM driver is being loaded.

Well, the drm driver is loaded by udev like everything else.

Dunno what plymouth (graphical boot screen tool) does to handle the
situation. I guess listening to udev events. So it should notice efifb
going away and drop the /dev/fb0 reference, but this races against
bochs-drm initializing.

> > Fix this by trying to wait until all references are gone. Don't wait
> > forever though given that userspace might keep the file handle open.
>
> Where does the 1s maximum delay come from?

Pulled out something out of thin air which I expect being on the safe
side. plymouth responding on the udev event should need only a small
fraction of that.

cheers,
Gerd

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