mt76: fix rounding issues on converting per-chain and combined txpower

Unify code converting between the different txpower values. Always add/remove
the combined txpower delta before dividing half-dB values.
Also fix the combined txpower delta values. The correct half-dB delta for
3 chains is 9, not 8.
Signed-off-by: NFelix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mac80211.c

@@ -1051,25 +1051,9 @@ int mt76_get_txpower(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 {
 	struct mt76_phy *phy = hw->priv;
 	int n_chains = hweight8(phy->antenna_mask);
+	int delta = mt76_tx_power_nss_delta(n_chains);
 
-	*dbm = DIV_ROUND_UP(phy->txpower_cur, 2);
-
-	/* convert from per-chain power to combined
-	 * output power
-	 */
-	switch (n_chains) {
-	case 4:
-		*dbm += 6;
-		break;
-	case 3:
-		*dbm += 4;
-		break;
-	case 2:
-		*dbm += 3;
-		break;
-	default:
-		break;
-	}
+	*dbm = DIV_ROUND_UP(phy->txpower_cur + delta, 2);
 
 	return 0;
 }

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

@@ -755,6 +755,13 @@ static inline bool mt76_is_skb_pktid(u8 pktid)
 	return pktid >= MT_PACKET_ID_FIRST;
 }
 
+static inline u8 mt76_tx_power_nss_delta(u8 nss)
+{
+	static const u8 nss_delta[4] = { 0, 6, 9, 12 };
+
+	return nss_delta[nss - 1];
+}
+
 void mt76_rx(struct mt76_dev *dev, enum mt76_rxq_id q, struct sk_buff *skb);
 void mt76_tx(struct mt76_phy *dev, struct ieee80211_sta *sta,
 	     struct mt76_wcid *wcid, struct sk_buff *skb);

drivers/net/wireless/mediatek/mt76/mt7615/init.c

@@ -269,6 +269,7 @@ mt7615_init_txpower(struct mt7615_dev *dev,
 	int i, n_chains = hweight8(dev->mphy.antenna_mask), target_chains;
 	u8 *eep = (u8 *)dev->mt76.eeprom.data;
 	enum nl80211_band band = sband->band;
+	int delta = mt76_tx_power_nss_delta(n_chains);
 
 	target_chains = mt7615_ext_pa_enabled(dev, band) ? 1 : n_chains;
 	for (i = 0; i < sband->n_channels; i++) {
@@ -283,21 +284,7 @@ mt7615_init_txpower(struct mt7615_dev *dev,
 			target_power = max(target_power, eep[index]);
 		}
 
-		target_power = DIV_ROUND_UP(target_power, 2);
-		switch (n_chains) {
-		case 4:
-			target_power += 6;
-			break;
-		case 3:
-			target_power += 4;
-			break;
-		case 2:
-			target_power += 3;
-			break;
-		default:
-			break;
-		}
-
+		target_power = DIV_ROUND_UP(target_power + delta, 2);
 		chan->max_power = min_t(int, chan->max_reg_power,
 					target_power);
 		chan->orig_mpwr = target_power;

drivers/net/wireless/mediatek/mt76/mt7615/mcu.c

@@ -1595,14 +1595,14 @@ int mt7615_mcu_rdd_send_pattern(struct mt7615_dev *dev)
 
 static void mt7615_mcu_set_txpower_sku(struct mt7615_phy *phy, u8 *sku)
 {
-	static const u8 nss_delta[4] = { 0, 6, 8, 12 };
 	struct mt76_phy *mphy = phy->mt76;
 	struct ieee80211_hw *hw = mphy->hw;
 	int n_chains = hweight8(mphy->antenna_mask);
 	int tx_power;
 	int i;
 
-	tx_power = hw->conf.power_level * 2 - nss_delta[n_chains - 1];
+	tx_power = hw->conf.power_level * 2 -
+		   mt76_tx_power_nss_delta(n_chains);
 	mphy->txpower_cur = tx_power;
 
 	for (i = 0; i < MT_SKU_1SS_DELTA; i++)
@@ -1612,7 +1612,8 @@ static void mt7615_mcu_set_txpower_sku(struct mt7615_phy *phy, u8 *sku)
 		int delta = 0;
 
 		if (i < n_chains - 1)
-			delta = nss_delta[n_chains - 1] - nss_delta[i];
+			delta = mt76_tx_power_nss_delta(n_chains) -
+				mt76_tx_power_nss_delta(i + 1);
 		sku[MT_SKU_1SS_DELTA + i] = delta;
 	}
 }