[ath9k-devel] QCA9558 problems for MCS 14/15

[Simon Wunderlich <simon@open-mesh.com>]

Hello ath9k-devs,

we have an issue with a new QCA9558 SoC based board (Rev 0, a 3x3 2.4G board). 
We were doing performance tests with various 2-stream 802.11n clients, but 
appearently the high MCS rates 14 and 15 can not be used reliably with ath9k - 
rc_stats show that transmission fail most of the time, and the connected 
clients don't receive them as well. The original firmware with an Atheros 9.5 
driver (9.5.3.15) does not show that behaviour and works fine. Therefore we 
assume that there is something missing/wrong in ath9k. Iperf tests in HT20 
showed 60 Mbit/s with ath9k and 80 Mbit/s with the original firmware (distance 
1-3 meter).

We have been in contact with Sujith who kindly helped us and checked for 
updates, thanks to his work some patches made it to the mailing list. However 
the problem is not yet solved on our AP, and while we are still working on it, 
I'd like to get your opinions as well.

What we did so far: We have tested Intel and Atheros clients (2-stream) which 
work fine with other Access Points. We have tested various driver versions 
(OpenWRT trunk, OpenWRT with manually backported drivers from latest wireless-
testing, including Sujiths latest patches). We have also tried different 
hardware samples. We experience the described problem in all of these 
combinations, ath9k/minstrel tops out at MCS12/13 maximum (manual setting 
MCS15 fails as well).

Any ideas and suggestions (also how to debug the problem further) would be 
very much appreciated.

Thank you,
   Simon