wifi: mt76: mt7921: fix missing mutex protection in multiple paths

The MT7921 driver has the same mutex protection bugs as MT7925 - they were
inherited when MT7925 was forked from MT7921. Several code paths iterate
over active interfaces and call MCU functions without proper mutex protection.

Add mutex protection in the following locations:

1. mt7921_set_runtime_pm() in main.c:
   Called when runtime PM settings change. The callback
   mt7921_pm_interface_iter() calls MCU functions that require
   the device mutex to be held.

2. mt7921_regd_set_6ghz_power_type() in main.c:
   Called during VIF add/remove for 6GHz power type determination.
   Uses ieee80211_iterate_active_interfaces() without mutex.

3. mt7921_mac_reset_work() in mac.c:
   After firmware recovery, iterates interfaces to reconnect them.
   The mt7921_vif_connect_iter() callback calls MCU functions.

4. mt7921_roc_abort_sync() in main.c:
   The function iterates interfaces and calls MCU functions via
   mt7921_roc_iter() callback. The mutex must be held during
   the iteration, not at call sites, to avoid nested mutex
   acquisition deadlocks in suspend paths.

These bugs can cause system hangs during:
- Power management state transitions
- WiFi reset/recovery
- Suspend/resume cycles
- 6GHz regulatory power type changes

The fix follows the same pattern used in the MT7925 patches, with
the mutex protection moved inside mt7921_roc_abort_sync() to avoid
deadlocks when called from suspend paths. Suspend paths (pci.c, sdio.c)
are updated to remove the outer mutex since mt7921_roc_abort_sync()
now handles mutex internally.

Signed-off-by: Zac Bowling <zac@zacbowling.com>

Author: zbowling

mt7921/mac.c

@@ -693,9 +693,11 @@ void mt7921_mac_reset_work(struct work_struct *work)
 	clear_bit(MT76_RESET, &dev->mphy.state);
 	pm->suspended = false;
 	ieee80211_wake_queues(hw);
+	mt792x_mutex_acquire(dev);
 	ieee80211_iterate_active_interfaces(hw,
 					    IEEE80211_IFACE_ITER_RESUME_ALL,
 					    mt7921_vif_connect_iter, NULL);
+	mt792x_mutex_release(dev);
 	mt76_connac_power_save_sched(&dev->mt76.phy, pm);
 }
 

mt7921/main.c

@@ -373,10 +373,13 @@ void mt7921_roc_abort_sync(struct mt792x_dev *dev)
 
 	del_timer_sync(&phy->roc_timer);
 	cancel_work_sync(&phy->roc_work);
-	if (test_and_clear_bit(MT76_STATE_ROC, &phy->mt76->state))
+	if (test_and_clear_bit(MT76_STATE_ROC, &phy->mt76->state)) {
+		mt792x_mutex_acquire(dev);
 		ieee80211_iterate_interfaces(mt76_hw(dev),
 					     IEEE80211_IFACE_ITER_RESUME_ALL,
 					     mt7921_roc_iter, (void *)phy);
+		mt792x_mutex_release(dev);
+	}
 }
 EXPORT_SYMBOL_GPL(mt7921_roc_abort_sync);
 
@@ -619,9 +622,11 @@ void mt7921_set_runtime_pm(struct mt792x_dev *dev)
 	bool monitor = !!(hw->conf.flags & IEEE80211_CONF_MONITOR);
 
 	pm->enable = pm->enable_user && !monitor;
+	mt792x_mutex_acquire(dev);
 	ieee80211_iterate_active_interfaces(hw,
 					    IEEE80211_IFACE_ITER_RESUME_ALL,
 					    mt7921_pm_interface_iter, dev);
+	mt792x_mutex_release(dev);
 	pm->ds_enable = pm->ds_enable_user && !monitor;
 	mt76_connac_mcu_set_deep_sleep(&dev->mt76, pm->ds_enable);
 }
@@ -765,9 +770,11 @@ mt7921_regd_set_6ghz_power_type(struct ieee80211_vif *vif, bool is_add)
 	struct mt792x_dev *dev = phy->dev;
 	u32 valid_vif_num = 0;
 
+	mt792x_mutex_acquire(dev);
 	ieee80211_iterate_active_interfaces(mt76_hw(dev),
 					    IEEE80211_IFACE_ITER_RESUME_ALL,
 					    mt7921_calc_vif_num, &valid_vif_num);
+	mt792x_mutex_release(dev);
 
 	if (valid_vif_num > 1) {
 		phy->power_type = MT_AP_DEFAULT;