Re: Compex WLE200NX: regdomain sanitized regression

[Kalle Valo <kvalo@kernel.org>]

Thorsten Leemhuis <regressions@leemhuis.info> writes:

> Hi, this is your Linux kernel regression tracker speaking.
>
> On 27.11.21 13:21, Nuno Oliveira wrote:
>> * Sebastian Bachmann <hello@reox.at> [2021-11-27 08:17]:
>>
>>> 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)
>> 
>> After June 2020 there were other users also affected by this change (see
>> e.g.,
>> https://lists.infradead.org/pipermail/ath10k/2021-August/012802.html).
>> Users were complaining that this change was too restrictive since it
>> meant that the intersection of restrictions for regdomains 0x00, 0x64,
>> US, and their local domain, together with a cumulative mode of applying
>> these constraints meant that, in practice, they would not be able to use
>> their world domain cards anymore as APs in the 5GHz band, for certain
>> regdomains where they were located.
>> 
>> And several people pinpointed the exact source changes responsible for
>> this. In my case, I ended up applying the attached patch, that just
>> loads the parameters for the regdomain that I'm interested in
>> (CTRY_PORTUGAL). I'm not in the US; and I care for their regulatory
>> restrictions as much as they are interested in mine.
>> 
>> So I think that you might be able to use the attached changes, with the
>> specific CTRY_xxx parameter suitable for your case. And then recompile
>> the respective Debian kernel package, which takes a lot of CPU if you
>> just recompile the whole package. Let me know if you need instructions.
>> 
>> A more robust option would be to go the OpenWRT way, and use their
>> patches to make this country selection a parameter for the kernel
>> module. This way, you would just reload the kernel module to change to a
>> new regdomain, subject to the restrictions of your hardware / firmware.
>> I have not looked into that. Please let me know if you isolate these
>> patches.
>> 
>> In any case it seems difficult to escape a kernel recompile, due to this
>> small, entirely legitimate, yet remarkable decision by the driver
>> maintainers.
>
> This is a regression due to 2dc016599cfa ("ath: add support for special
> 0x0 regulatory domain") that seems to affect quite a few users, but
> afaics was never properly addressed. I fully understand that this might
> be a special case where Linus' "no regressions" rule can't be simply
> applied.

Yes, this is a tricky problem and I am taking a second look at this.
Regulatory rules are complicated and we do not want to break them in any
circumstance.

I see two ways to workaround this:

1) calibrate your board with a correct country code (which is impossible
   for an average user)

2) use 2.4 GHz band

> But isn't there some way to provide users with a solution that doesn't
> force users to compile a module or a kernel? Like a module-parameter
> that only works if the the regulatory domain code in the EEPROM is empty
> (as apparently used by OpenWRT?). Yes, module parameters are normally a
> bad idea, but this case it might be a situation where it's the best
> solution.

I don't think setting the country code via a module parameter would be
acceptable for the authorities, more info here:

https://wireless.wiki.kernel.org/en/developers/regulatory

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