5Ghz WiFi blocked by vc4.ko on kernel 5.10.12 on RPi4B 8GB

Ryutaroh Matsumoto ryutaroh at ict.e.titech.ac.jp
Thu Feb 11 00:52:12 EST 2021

Hi Maxime, thank you for your response.

> And does fkms (or the simplefb driver at 1440p) show the same behaviour?

I do not think we can use fkms by the plain upstream kernel
(am I right?).

I found that giving


to config.txt makes simple framebuffer to use 3840x2160 with my display
(refresh rate unknown). With that setup, I can use 5GHz wifi but cannot use
2.4GHz wifi. Without hdmi_enable_4kp60=1, the output resolution is much
lower, but usablity of WiFi remains the same.

With vc4.ko, neither 2.4GHz or 5GHz passes ping packegs.

In all cases, WiFi association to SSIDs can be established.

Since 5GHz WiFi can only be used with module_blacklist=vc4,
I have been blacklisting vc4.ko for a while...

I am seeing the above with Debian kernel 5.10.12.

Besides, I am also experience instability of audio device driver
only when vc4.ko is loaded as reported at

Best regards, Ryutaroh

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