ath9k: Add information about antenna diversity

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/antenna.c

@@ -16,6 +16,58 @@
 
 #include "ath9k.h"
 
+/*
+ * AR9285
+ * ======
+ *
+ * EEPROM has 2 4-bit fields containing the card configuration.
+ *
+ * antdiv_ctl1:
+ * ------------
+ * bb_enable_ant_div_lnadiv : 1
+ * bb_ant_div_alt_gaintb    : 1
+ * bb_ant_div_main_gaintb   : 1
+ * bb_enable_ant_fast_div   : 1
+ *
+ * antdiv_ctl2:
+ * -----------
+ * bb_ant_div_alt_lnaconf  : 2
+ * bb_ant_div_main_lnaconf : 2
+ *
+ * The EEPROM bits are used as follows:
+ * ------------------------------------
+ *
+ * bb_enable_ant_div_lnadiv      - Enable LNA path rx antenna diversity/combining.
+ *                                 Set in AR_PHY_MULTICHAIN_GAIN_CTL.
+ *
+ * bb_ant_div_[alt/main]_gaintb  - 0 -> Antenna config Alt/Main uses gaintable 0
+ *                                 1 -> Antenna config Alt/Main uses gaintable 1
+ *                                 Set in AR_PHY_MULTICHAIN_GAIN_CTL.
+ *
+ * bb_enable_ant_fast_div        - Enable fast antenna diversity.
+ *                                 Set in AR_PHY_CCK_DETECT.
+ *
+ * bb_ant_div_[alt/main]_lnaconf - Alt/Main LNA diversity/combining input config.
+ *                                 Set in AR_PHY_MULTICHAIN_GAIN_CTL.
+ *                                 10=LNA1
+ *                                 01=LNA2
+ *                                 11=LNA1+LNA2
+ *                                 00=LNA1-LNA2
+ *
+ * AR9485 / AR9565 / AR9331
+ * ========================
+ *
+ * The same bits are present in the EEPROM, but the location in the
+ * EEPROM is different (ant_div_control in ar9300_BaseExtension_1).
+ *
+ * ant_div_alt_lnaconf      ==> bit 0~1
+ * ant_div_main_lnaconf     ==> bit 2~3
+ * ant_div_alt_gaintb       ==> bit 4
+ * ant_div_main_gaintb      ==> bit 5
+ * enable_ant_div_lnadiv    ==> bit 6
+ * enable_ant_fast_div      ==> bit 7
+ */
+
 static inline bool ath_is_alt_ant_ratio_better(int alt_ratio, int maxdelta,
 					       int mindelta, int main_rssi_avg,
 					       int alt_rssi_avg, int pkt_count)