Bug#968181: linux-image-5.7.0-2-arm64: DRM unavailable on Rapsberry Pi 4B

[Ryutaroh Matsumoto <ryutaroh@ict.e.titech.ac.jp>]

Control: forwarded -1 https://github.com/raspberrypi/firmware/issues/1247
Control: tags -1 + fixed-upstream

> On the other hand, gdm3 and weston gives the following error in dmesg,
> "kernel: [drm:vc4_bo_create [vc4]] *ERROR* Failed to allocate from CMA:"
> and no graphics come. Rendering by wayland does not work at all with
> vc4.ko in 5.10.9.

The above symptom is "fixed" by adding
CMA=256M@128M
to the kernel command line.

Then the gdm3 display manager starts up well, and I have
# grep -i cma /proc/meminfo 
CmaTotal:         262144 kB
CmaFree:          143008 kB

Best regards, Ryutaroh Matsumoto