brcmfmac disconnects AP mode while scanning

brcmfmac disconnects AP mode while scanning

[KeithG]

I posted this over on the linux-wireless board as well but did not
learn much towards a fix.

We are using iwd to manage the wireless on RPis. We discovered that
when the brcmfmac in the Pi is set to be in AP mode and then iwd
initiates a scan on the interface, all clients on the AP are
disconnected. This is unexpected and does not happen when
wpa_supplicant is used then scans.

I have been discussing this with one of the IWD devs and he pinpointed
it to the fact that when iwd scans, it is using 'passive scan' to scan
for ssids and when it does it shuts down the AP. We do not witness
this behavior with intel cards and it also does not happen when
wpa_supplicant is used instead of iwd and then it scans for ssids. The
dev determined that wpa_suplicant uses 'active scan' and when it scans
for ssids whereas iwd uses 'passive scan'. Our Pis are stable with
wpa_supplicant/Hostapd, but not with iwd. We prefer using iwd.

He passed on some patches that change the behavior of iwd to only use
'active scans'. With iwd built with these patches (only to use active
scan) the AP is stable when iwd scans for ssids.
This behavior/modification is not consistent with other cards, though.
The question is: why are we seeing this behavior on brcmfmac? Is
wpa_suplicant doing it properly and iwd not? If so, why? Could the
brcmfmac driver be patched so that iwd will work properly with a
passive scan and not disconnect all AP connected clients?

Keith