Matthias May wrote:
> I'm in the position where i want to use a 9390 as 2x2 instead of 3x3.
> I use backports-3.12-1.
> I've set the rx and tx mask in eeprom to 0x5.

0x5 is not a valid chainmask on AR9390. The official statement is:

"We intentionally didn’t productize the chain mask of 0x5 on AR9380/AR9580
because of the complexities of register addressing and getting through the ASIC
self-calibrations in this configuration."

I think for 2x2 operation, 0x3 is the only option. The problem with Chain-1
(which was mentioned in 
http://www.spinics.net/lists/linux-wireless/msg114607.html)
is probably for a specific board. So maybe you can just set 0x3 using iw and
see if things are okay.

> Nov 18 13:39:45 CHD500279 kernel: [16510.563694] ath: phy11: NF calibrated 
> [ctl] [chain 0] is -105
> Nov 18 13:39:45 CHD500279 kernel: [16510.563698] ath: phy11: NF calibrated 
> [ctl] [chain 2] is -50
> Nov 18 13:39:45 CHD500279 kernel: [16510.563701] ath: phy11: NF[2] (-50) > 
> MAX (-100), correcting to MAX
> Nov 18 13:39:45 CHD500279 kernel: [16510.563705] ath: phy11: NF calibrated 
> [ext] [chain 0] is -105
> Nov 18 13:39:45 CHD500279 kernel: [16510.563708] ath: phy11: NF calibrated 
> [ext] [chain 2] is -50
> Nov 18 13:39:45 CHD500279 kernel: [16510.563712] ath: phy11: NF[5] (-50) > 
> MAX (-100), correcting to MAX

Again, this is the side effect of using the unsupported mask, 0x5.

But, this is also a bug in ath9k. Right now the CCA registers assigned
in ar9003_hw_attach_phy_ops() are used in a sequential manner.

But, as per our systems engineers:

AR_PHY_CCA_0 - for 1st active chain, (value always valid).
AR_PHY_CCA_1 - for 2nd active chain, (value should be ignored except for chain 
mask 3,5,7).
AR_PHY_CCA_2 - for 3rd active chain, (value should be ignored except for chain 
mask 7).

So, if 0x5 is used, AR_PHY_CCA_0 and AR_PHY_CCA_1 should be used.
But, ath9k currently uses AR_PHY_CCA_0 and AR_PHY_CCA_2 for 0x5
(in ar9003_hw_do_getnf).

In any case, I don't think this needs to be fixed, since 0x5 is invalid.

Sujith
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