mt76: MT7921K monitor mode not working

[Lorenzo Bianconi]

> Hi,

Hi Jan,

> 
> we are not able to obtain any packets when packet capturing with the
> Mediatek MT7921K in monitor mode on 2.4, 5 and 6 GHz.
> tcpdump will show you 0 recorded packets. When doing a "iw dev wls1 scan" on
> a parallel running managed interface on the same phy, the packet capture
> will contain beacons and probe responses from the scan though.
> Can anyone confirm that?
> 
> mt76 (https://github.com/openwrt/mt76/commits/master): commit
> 6fad970893dd26ef6e6c8344b958344254f6362a (HEAD -> master, origin/master,
> origin/HEAD)
> Kernel: 5.16.0-rc2-next-20211124+
> WM Firmware Version: ____010000, Build Time: 20211014150922

IIRC you need to disable runtime-pm and deep-sleep to proper enable monitor
mode:

echo 0 > /sys/kernel/debug/ieee80211/phy<x>/mt76/runtime-pm
echo 0 > /sys/kernel/debug/ieee80211/phy<x>/mt76/deep-sleep

Can you please give it whirl?

Regards,
Lorenzo

> 
> Steps to reproduce:
> sudo iw dev wls1 del
> sudo iw phy phy0 interface add mon0 type monitor
> sudo ip link set dev mon0 up
> sudo iw dev mon0 set freq 6115
> sudo tcpdump -i mon0 -w 6g-capture.pcap
> 
> Kinds regards, Jan
> 
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