mt76: MT7921K monitor mode not working

[Sven Eckelmann]

On Saturday, 4 December 2021 01:55:04 CET sean.wang at mediatek.com wrote:
> >ack, I agree, but I guess the point here is what is the difference (from the fw pov) if you disable runtime-pm/deep-sleep before/after the vif is added. I guess it is supposed to be the same, right?
> 
> yes, it is supposed to be the same.

Two things which were noticed too:

First finding: If I run `iw dev mon0 del` after a non-working tcpdump dump 
session then I get following error messages before my complete system freezes:

    [  492.812050] mt7921e 0000:04:00.0: Message 40000002 (seq 14) timeout
    [  492.818587] mt7921e 0000:04:00.0: chip reset
    [  495.883934] mt7921e 0000:04:00.0: Message 00000046 (seq 15) timeout

Second one: We cannot see beacons on 2.4Ghz and 5GHz when runtime-pm + deep-
sleep is set to 0.



Regarding the initial problem: following works (when ignoring the missing 
beacons for now):

    echo 0 > /sys/kernel/debug/ieee80211/phy0/mt76/runtime-pm
    echo 0 > /sys/kernel/debug/ieee80211/phy0/mt76/deep-sleep
    iw dev wlp4s0 del
    iw phy0 interface add mon0 type monitor
    ip link set up dev mon0
    iw dev mon0 set channel 11
    tcpdump -ni mon0


What is often not working:

    iw dev wlp4s0 del
    iw phy0 interface add mon0 type monitor
    ip link set up dev mon0
    iw dev mon0 set channel 11
    tcpdump -ni mon0 &
    sleep 10
    echo 0 > /sys/kernel/debug/ieee80211/phy0/mt76/runtime-pm
    sleep 5
    echo 0 > /sys/kernel/debug/ieee80211/phy0/mt76/deep-sleep


What I have seem to break sometimes (but cannot reproduce reliably):

    iw dev wlp4s0 del
    iw phy0 interface add mon0 type monitor
    ip link set up dev mon0
    iw dev mon0 set channel 11
    echo 0 > /sys/kernel/debug/ieee80211/phy0/mt76/runtime-pm
    echo 0 > /sys/kernel/debug/ieee80211/phy0/mt76/deep-sleep
    tcpdump -ni mon0


The channel 11 is rather busy. It is for example also used for our community 
mesh network in the city center - so is rather easy for me to see that it is 
able to sniff traffic or not.

Kind regards,
	Sven
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