KMS seems broken in vc4.ko

[Ryutaroh Matsumoto]

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.

> 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??

Best regards, Ryutaroh