Re: Missing scan results with SCAN_FLAG_COLOCATED_6GHZ set (Ath11k/WCN6855)

[Ben Greear <greearb@candelatech.com>]

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,
Ben

> 
> Thanks,
> 
> James
> 
> 

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com