Missing scan results with SCAN_FLAG_COLOCATED_6GHZ set (Ath11k/WCN6855)
James Prestwood
prestwoj at gmail.com
Fri Oct 4 11:46:54 PDT 2024
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.
Thanks,
James
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