Missing scan results with SCAN_FLAG_COLOCATED_6GHZ set (Ath11k/WCN6855)

[James Prestwood]

Hi Ben,

On 10/4/24 12:18 PM, Ben Greear wrote:
> On 10/4/24 11:46, James Prestwood wrote:
>> Hi,
>>
>> I've noticed that when setting the colocated flag much of the scan 
>> results are not appearing when they should be. This was seen in a 
>> large warehouse where our network/SSID was using only the 6ghz band. 
>> There were other networks on 2.4/5ghz though, which maybe is having 
>> some effect, but those networks are not broadcasting on 6ghz.
>>
>> This first came to my attention when the majority of our clients were 
>> experiencing horrible signal quality. Upon looking at the logs and 
>> nl80211 messages to the kernel IWD was issuing both limited 6ghz 
>> scans as well as full spectrum scans and only showing a few 6ghz 
>> results, like 1-2 BSS's which should not have been the case. I was 
>> able to scan manually using "iw scan" and I saw all the expected 
>> BSS's. I isolated it to the fact that IWD was setting the 
>> SCAN_FLAG_COLOCATED_6GHZ and removing that flag resulted in all the 
>> BSS's showing up in scan results. Note, that with or without the flag 
>> all the 2.4/5ghz BSS's were showing up without a problem, it seems 
>> completely isolated to the 6ghz band.
>>
>> The NEW_SCAN_RESULTS event was indicating the kernel had scanned all 
>> the expected frequencies we were asking to scan, but the results were 
>> mostly empty for 6ghz. Only ever the connected BSS would show up and 
>> _sometimes_ another BSS, but generally not.
>>
>> I'm trying to read through the code associated with the COLOCATED 
>> flag, but its not exactly intuitive (to me at least). I'm not sure if 
>> this is something with mac80211 or at the driver level. I really 
>> don't have anything to compare it to as ath11k is the only hardware 
>> available at this warehouse with many APs around.
>>
>> I'm looking for some guidance on if this is expected behavior with 
>> the colocated flag, and if there is any concern with including it 
>> unconditionally on every scan. If it has unintended consequences like 
>> this, generally, across multiple drivers I'd like to re-think its use 
>> in IWD.
>
> I had some similar issues using hostap, and hacked it to do every 4th 
> or so scan with that
> flag set differently.  Hopefully that lets the 'fast' scan work when 
> it can, but still lets one
> scan the hard way...
>
> Possibly there are driver concerns too, I was using Intel be200 when 
> debugging this.

Thanks for the extra info. Seems like a mac80211 quirk if its also on an 
Intel card. Long term I may just parse RNR elements in userspace and 
issue extra scans if needed.

Thanks,

James