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>

drivers/net/wireless/iwlwifi/iwl-agn-lib.c

@@ -274,9 +274,20 @@ void iwlagn_send_advance_bt_config(struct iwl_priv *priv)
 		return;
 	}
 
+	/*
+	 * Possible situations when BT needs to take over for receive,
+	 * at the same time where STA needs to response to AP's frame(s),
+	 * reduce the tx power of the required response frames, by that,
+	 * allow the concurrent BT receive & WiFi transmit
+	 * (BT - ANT A, WiFi -ANT B), without interference to one another
+	 *
+	 * Reduced tx power apply to control frames only (ACK/Back/CTS)
+	 * when indicated by the BT config command
+	 */
 	basic.kill_ack_mask = priv->kill_ack_mask;
 	basic.kill_cts_mask = priv->kill_cts_mask;
-	basic.reduce_txpower = priv->reduced_txpower;
+	if (priv->reduced_txpower)
+		basic.reduce_txpower = IWLAGN_BT_REDUCED_TX_PWR;
 	basic.valid = priv->bt_valid;
 
 	/*
@@ -590,6 +601,15 @@ static bool iwlagn_set_kill_msk(struct iwl_priv *priv,
 	return need_update;
 }
 
+/*
+ * Upon RSSI changes, sends a bt config command with following changes
+ *  1. enable/disable "reduced control frames tx power
+ *  2. update the "kill)ack_mask" and "kill_cts_mask"
+ *
+ * If "reduced tx power" is enabled, uCode shall
+ *  1. ACK/Back/CTS rate shall reduced to 6Mbps
+ *  2. not use duplciate 20/40MHz mode
+ */
 static bool iwlagn_fill_txpower_mode(struct iwl_priv *priv,
 				struct iwl_bt_uart_msg *uart_msg)
 {

drivers/net/wireless/iwlwifi/iwl-commands.h

@@ -1910,6 +1910,8 @@ enum iwl_bt_kill_idx {
 					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 @@ struct iwl_basic_bt_cmd {
 	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;