Compex WLE200NX: regdomain sanitized regression

[Sebastian Bachmann]

Hello,

I recently upgraded my Debian based AP from buster to bullseye, just to 
find out that hostapd does not work any more, because all 5GHz channels 
are marked as No-IR. This regression was already discussed on this ML 
here: https://www.mail-archive.com/ath10k@lists.infradead.org/msg12018.html
and there is also an entry in Debian's bug tracker for the same issue: 
https://bugs.debian.org/959821

I have a slightly different card (branded Compex WLE200NX):
04:00.0 Network controller: Qualcomm Atheros AR928X Wireless Network 
Adapter (PCI-Express) (rev 01)
         Subsystem: Qualcomm Atheros AR928X Wireless Network Adapter 
(PCI-Express)
         Kernel driver in use: ath9k
         Kernel modules: ath9k

But as you can see, also the EEPROM gets sanitized:
[   15.461755] ath9k 0000:04:00.0: enabling device (0000 -> 0002)
[   15.911600] ath: EEPROM regdomain sanitized
[   15.911612] ath: EEPROM regdomain: 0x64
[   15.911615] ath: EEPROM indicates we should expect a direct regpair map
[   15.911625] ath: Country alpha2 being used: 00
[   15.911628] ath: Regpair used: 0x64

I read in the other thread, that this is a regression, but the actual 
commit causing it was never reverted.
I tried to search for newer messages explaining the issue, however as 
far as I can tell, the thread ends in June 2020 with no solution available.

Therefore, I kindly want to ask if there is any workaround available to 
re-enable 5GHz channels in AP mode for my card? (expect sticking to a 
pre-5.6 kernel or manually patching and recompiling ath)

Best,
Sebastian