mt7603 not entering dynamic power save at association, only after explicit power save frame

[wryun]

The STA may use the SM Power Save frame to communicate its SM power save state. The STA may also use SM Power Save subfield in the HT Capabilities element of its (Re)Association Request frame to achieve the same purpose. The latter allows the STA to use only a single receive chain immediately after (re)association.

Unfortunately, it seems like it's only if an explicit action frame is sent that this is working (at least with an iwlwifi station connected to an mt7603 access point). i.e. on connection, the AP sends at MCS15 without RTS/CTS, and it's only after toggling power_save on/off on the iwlwifi station that that AP uses RTS/CTS.

[wryun]

On further investigation, it seems like the SMPS command to the MCU is applied too early (before assocation). Or at least things work better if I do:

--- a/mt7603/main.c
+++ b/mt7603/main.c
@@ -373,6 +373,12 @@ mt7603_sta_assoc(struct mt76_dev *mdev, struct ieee80211_vif *vif,
                 struct ieee80211_sta *sta)
 {
        struct mt7603_dev *dev = container_of(mdev, struct mt7603_dev, mt76);
+       struct mt7603_sta *msta = (struct mt7603_sta *)sta->drv_priv;
+
+       // Once association has happened, we need to make sure that the SMPS
+       // mode is set again (if it's happened earlier, the firmware seems to forget
+       // about it, at least in terms of the observed behaviour).
+       msta->smps = ~0;
 
        mt7603_wtbl_update_cap(dev, sta);
 }

This forces the SMPS command to run after association, and the observed behaviour is now correct (i.e. RTS/CTS).