mt76: mt7921: fix a possible race enabling/disabling runtime-pm

Fix a possible race enabling/disabling runtime-pm between
mt7921_pm_set() and mt7921_poll_rx() since mt7921_pm_wake_work()
always schedules rx-napi callback and it will trigger
mt7921_pm_power_save_work routine putting chip to in low-power state
during mt7921_pm_set processing.

Suggested-by: Deren Wu <deren.wu@mediatek.com>
Tested-by: Deren Wu <deren.wu@mediatek.com>
Fixes: 1d8efc7 ("mt76: mt7921: introduce Runtime PM support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/0f3e075a2033dc05f09dab4059e5be8cbdccc239.1640094847.git.lorenzo@kernel.org

drivers/net/wireless/mediatek/mt76/mt76_connac_mac.c

@@ -7,9 +7,6 @@ int mt76_connac_pm_wake(struct mt76_phy *phy, struct mt76_connac_pm *pm)
 {
 	struct mt76_dev *dev = phy->dev;
 
-	if (!pm->enable)
-		return 0;
-
 	if (mt76_is_usb(dev))
 		return 0;
 

drivers/net/wireless/mediatek/mt76/mt7921/debugfs.c

@@ -276,7 +276,7 @@ mt7921_pm_set(void *data, u64 val)
 	struct mt7921_dev *dev = data;
 	struct mt76_connac_pm *pm = &dev->pm;
 
-	mt7921_mutex_acquire(dev);
+	mutex_lock(&dev->mt76.mutex);
 
 	if (val == pm->enable)
 		goto out;
@@ -285,16 +285,22 @@ mt7921_pm_set(void *data, u64 val)
 		pm->stats.last_wake_event = jiffies;
 		pm->stats.last_doze_event = jiffies;
 	}
-	pm->enable = val;
+	/* make sure the chip is awake here and ps_work is scheduled
+	 * just at end of the this routine.
+	 */
+	pm->enable = false;
+	mt76_connac_pm_wake(&dev->mphy, pm);
 
 	ieee80211_iterate_active_interfaces(mt76_hw(dev),
 					    IEEE80211_IFACE_ITER_RESUME_ALL,
 					    mt7921_pm_interface_iter, dev);
 
 	mt76_connac_mcu_set_deep_sleep(&dev->mt76, pm->ds_enable);
 
+	pm->enable = val;
+	mt76_connac_power_save_sched(&dev->mphy, pm);
 out:
-	mt7921_mutex_release(dev);
+	mutex_unlock(&dev->mt76.mutex);
 
 	return 0;
 }