ath9k: Add information about antenna diversity

#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)