ath9k: adjust tx power reduction for US regulatory domain

FCC regulatory rules allow for up to 3 dBi antenna gain. Account for
this in the EEPROM based tx power reduction code.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/kernel/mac80211/patches/330-ath9k-adjust-tx-power-reduction-for-US-regulatory-do.patch

@@ -0,0 +1,23 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Wed, 19 Jul 2017 08:49:31 +0200
+Subject: [PATCH] ath9k: adjust tx power reduction for US regulatory domain
+
+FCC regulatory rules allow for up to 3 dBi antenna gain. Account for
+this in the EEPROM based tx power reduction code.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/drivers/net/wireless/ath/ath9k/hw.c
++++ b/drivers/net/wireless/ath/ath9k/hw.c
+@@ -2954,6 +2954,10 @@ void ath9k_hw_apply_txpower(struct ath_h
+ 	if (ant_gain > max_gain)
+ 		ant_reduction = ant_gain - max_gain;
+ 
++	/* FCC allows maximum antenna gain of 3 dBi */
++	if (reg->region == NL80211_DFS_FCC)
++		ant_reduction = min_t(int, ant_reduction - 6, 0);
++
+ 	ah->eep_ops->set_txpower(ah, chan, ctl, ant_reduction, new_pwr, test);
+ }
+