vc4.ko causes another misterious error

[Ryutaroh Matsumoto]

Hi Nicolas, thank you for your reply.

>> I found another mysterious error caused by vc4.ko.
>> Only when vc4.ko is loaded AND the SD card slot is empty in my RPi4B 8GB,
>> I observe the following harmless error message at every 10 seconds:
>> 
>> [  255.457584] mmc1: Timeout waiting for hardware cmd interrupt.
> I've been looking at this issue for a while already. See here[1], it's not yet
> ready for merging, I'm waiting for someone with access to proper documentation
> to comment on it. But it does the trick.

>From  https://lore.kernel.org/linux-mmc/20210322185816.27582-1-nsaenz@kernel.org/
>I found out that by bumping the controller's frequency to 150MHz the
>issue disapears. So let's do that.

I wonder if 150MHz is enough for 4K 60fps display output of RPi4B
(I am using 4K 30fps display).

Best regards, Ryutaroh