mt76: mt7615: fix getting maximum tx power from eeprom

On top of the EEPROM target power, each rate can also has a power offset.
On many devices, this power offset is used to boost the tx power of lower
rates. Take this into account when parsing rate power.
The assumption here is, that the first rate (OFDM 6M or CCK 1M) has the
highest tx power
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7615/eeprom.h

@@ -32,6 +32,8 @@ enum mt7615_eeprom_field {
 	MT_EE_TX0_2G_TARGET_POWER =		0x058,
 	MT_EE_TX0_5G_G0_TARGET_POWER =		0x070,
 	MT_EE_TX1_5G_G0_TARGET_POWER =		0x098,
+	MT_EE_2G_RATE_POWER =			0x0be,
+	MT_EE_5G_RATE_POWER =			0x0d5,
 	MT_EE_EXT_PA_2G_TARGET_POWER =		0x0f2,
 	MT_EE_EXT_PA_5G_TARGET_POWER =		0x0f3,
 	MT7663_EE_TX0_2G_TARGET_POWER =		0x123,
@@ -43,6 +45,10 @@ enum mt7615_eeprom_field {
 	MT7663_EE_MAX =				0x400,
 };
 
+#define MT_EE_RATE_POWER_MASK			GENMASK(5, 0)
+#define MT_EE_RATE_POWER_SIGN			BIT(6)
+#define MT_EE_RATE_POWER_EN			BIT(7)
+
 #define MT_EE_CALDATA_FLASH_TX_DPD		BIT(0)
 #define MT_EE_CALDATA_FLASH_RX_CAL		BIT(1)
 

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

@@ -198,6 +198,17 @@ void mt7615_init_txpower(struct mt7615_dev *dev,
 	u8 *eep = (u8 *)dev->mt76.eeprom.data;
 	enum nl80211_band band = sband->band;
 	int delta = mt76_tx_power_nss_delta(n_chains);
+	u8 rate_val;
+
+	/* assume the first rate has the highest power offset */
+	if (band == NL80211_BAND_2GHZ)
+		rate_val = eep[MT_EE_2G_RATE_POWER];
+	else
+		rate_val = eep[MT_EE_5G_RATE_POWER];
+
+	if ((rate_val & ~MT_EE_RATE_POWER_MASK) ==
+	    (MT_EE_RATE_POWER_EN | MT_EE_RATE_POWER_SIGN))
+		delta += rate_val & MT_EE_RATE_POWER_MASK;
 
 	target_chains = mt7615_ext_pa_enabled(dev, band) ? 1 : n_chains;
 	for (i = 0; i < sband->n_channels; i++) {