ath9k_hw: Fix Tx IQ Calibration hang issue in AR9003 chips

ath9k_hw: Fix Tx IQ Calibration hang issue in AR9003 chips

On AR9003 chips, doing three IQ calibrations will possibly cause chip
in stuck state. In noisy environment, chip could receive
a packet during the middle of three calibrations and it causes
the conflict of HW access and the eventual failure. It also
causes IQ calibration outliers which results in poor Tx EVM.

The IQ Cal procedure is after resetting the chip, run IQ cal 3 times
per each cal cycle and find the two closest readings and average of two.
The advantage of running Tx IQ cal more than once is that we can compare
calibration results for the same gain setting over multiple iterations.
Most of the cases the IQ failures were observed after first pass.

For the AR9485 and later chips, Tx IQ Calibration is performed along
with AGC cal. But for pre-AR9485 chips, Tx IQ cal HW has to be separated
from the rest of calibration HW to avoid chip hang. After all
calibrations are done in HW, we can start SW post-processing.
By doing this way, we minimize the SW difference among all chips.

The order of calibration (run IQ cal before other calibration) is also
needed to avoid chip hang for chips before AR9485. This issue was
originally observed with AR9382.

During the issue kernel log was filled with following message
ath: timeout (100000 us) on reg 0xa640: 0x00000001 & 0x00000001 != 0x00000000
ath: timeout (100000 us) on reg 0xa2c4: 0x00158dd9 & 0x00000001 != 0x00000000
ath: Unable to reset channel (2412 MHz), reset status -5
ath: Unable to set channel

Signed-off-by: Rajkumar Manoharan <rmanoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>