iwlwifi: add documentation for bt reduced tx power

Change-Id: Ia6294d651dcffdcaf8b62e67bcef52bd8c158dea
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Reviewed-on: http://git-mwg.jer.intel.com/gerrit/1947
Tested-by: Jenkins
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-commands.h b/drivers/net/wireless/iwlwifi/iwl-commands.h
index 83a6930..2813a0a 100644
--- a/drivers/net/wireless/iwlwifi/iwl-commands.h
+++ b/drivers/net/wireless/iwlwifi/iwl-commands.h
@@ -1910,6 +1910,8 @@
 					IWLAGN_BT_VALID_REDUCED_TX_PWR | \
 					IWLAGN_BT_VALID_3W_LUT)
 
+#define IWLAGN_BT_REDUCED_TX_PWR	BIT(0)
+
 #define IWLAGN_BT_DECISION_LUT_SIZE	12
 
 struct iwl_basic_bt_cmd {
@@ -1923,6 +1925,10 @@
 	u8 bt3_timer_t2_value;
 	__le16 bt4_reaction_time; /* unused */
 	__le32 bt3_lookup_table[IWLAGN_BT_DECISION_LUT_SIZE];
+	/*
+	 * bit 0: use reduced tx power for control frame
+	 * bit 1 - 7: reserved
+	 */
 	u8 reduce_txpower;
 	u8 reserved;
 	__le16 valid;