KMS seems broken in vc4.ko

[Maxime Ripard]

On Tue, Mar 16, 2021 at 07:08:50AM +0900, Ryutaroh Matsumoto wrote:
> Hi Maxime, thank you for your response.
> 
> > I'm not sure I follow you, last time you reported something you had to
> > blacklist vc4, not v3d?
> 
> Sure.
> 
> The context which I black-listed v3d.ko was
> https://github.com/raspberrypi/linux/issues/4202
> which was a "feature" (seems bug to me) only in Raspberry Pi OS...
> By investigating the above issue, I found that kmscube fails with vc4.ko.
> 
> The reported symptom here was, of course, verified with vc4.ko loaded.

I'm still confused, did you blacklist vc4 or v3d? 

> > v3d provides the 3d hardware acceleration on the bcm2711, so it's not
> > surprising to me that kmscube would fail if it's not there
> 
> Lucas provided a detailed analysis at the downstream bug report
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=985121#22
> By strace, he identified that kmscube fails at
> ioctl(3, DRM_IOCTL_MODE_SETCRTC, 0xffffc6e78bb0) = -1 EACCES (Permission denied)
> 
> Is it an expected behavior??

I mean, it depends on what mesa and kmscube are trying to do? Can you
enable drm.debug and see if there's any clearer error message?

Maxime
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