drm/vc4: module dysfunctional on Raspberry Pi 3B as of 5.18.0

[Maxime Ripard]

On Wed, Jun 08, 2022 at 04:14:22PM +0100, Peter Robinson wrote:
> > > > As of Linux 5.18.0, module vc4 apparently isn't working on Raspberry Pi
> > > > 3B any more.
> > > >
> > > > If a monitor is attached to the device, the boot messages show up as
> > > > usual, but right when KMS starts, the screen turns black. Similarly, the
> > > > screen also turns black when the module is blacklisted at boot time and
> > > > loaded from the running system.
> > > > The problem looks quite similar to the one posted some months ago in [1].
> >
> > If I understand you properly, it results in a blank screen if the
> > monitor is connected, but the system is still responsive?
> 
> Yes, it boots fine, I see all serial console output and the module
> loads etc, without a screen I didn't notice the issue
> 
> > If so, it's a very different problem than the link you provided, since
> > it was occurring when no monitor was connected and resulted in a total
> > system hang.
> >
> > > > Unfortunately, looking through systemd's journal didn't seem to yield
> > > > any real hint. Nevertheless, the results from grepping vc4 are
> > >
> > > I'm seeing the same issue with vc4 on a RPi3 on 5.18.1 on Fedora so
> > > can confirm the regression. Maxime would know what might be up here?
> >
> > I tested on 5.18 on my 3B and it works well. Could you paste your kernel
> > configuration and config.txt somewhere?
> 
> It boots with output on 5.17.13, and not on 5.18.

Interestingly, it works for 5.18 in my case but doesn't for the current
drm-misc-next branch with similar symptoms.

I'll look into that one and see if the two might be related.

Thanks!
Maxime
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