mt76: mt7603: add upper limit for dynamic sensitivity minimum receive power

If the minimum power is raised too much, it can make it impossible for weaker
clients to connect, and there are some scenarios where the false detects will
not go down no matter how much the sensitivity is adjusted.
Fixes connectivity issues in some rare cases
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7603/debugfs.c

@@ -121,4 +121,6 @@ void mt7603_init_debugfs(struct mt7603_dev *dev)
 				    mt7603_reset_read);
 	debugfs_create_devm_seqfile(dev->mt76.dev, "radio", dir,
 				    mt7603_radio_read);
+	debugfs_create_u8("sensitivity_limit", 0600, dir,
+			    &dev->sensitivity_limit);
 }

drivers/net/wireless/mediatek/mt76/mt7603/init.c

@@ -540,6 +540,7 @@ int mt7603_register_device(struct mt7603_dev *dev)
 		dev->mphy.antenna_mask = 1;
 
 	dev->slottime = 9;
+	dev->sensitivity_limit = 28;
 
 	ret = mt7603_init_hardware(dev);
 	if (ret)

drivers/net/wireless/mediatek/mt76/mt7603/mac.c

@@ -1750,7 +1750,8 @@ mt7603_false_cca_check(struct mt7603_dev *dev)
 	min_signal -= 15;
 
 	false_cca = dev->false_cca_ofdm + dev->false_cca_cck;
-	if (false_cca > 600) {
+	if (false_cca > 600 &&
+	    dev->sensitivity < -100 + dev->sensitivity_limit) {
 		if (!dev->sensitivity)
 			dev->sensitivity = -92;
 		else

drivers/net/wireless/mediatek/mt76/mt7603/mt7603.h

@@ -143,6 +143,7 @@ struct mt7603_dev {
 	u8 ed_strong_signal;
 
 	s8 sensitivity;
+	u8 sensitivity_limit;
 
 	u8 beacon_check;
 	u8 tx_hang_check;