The AR9285 antenna diversity code, ported from Linux ath9k, seems to be making sub-optimal choices for antenna diversity.
An example of normal readings:
ar9285_ant_comb_scan: main: 61, alt: 22, rx_ant_conf: 0, main_ant_conf: 3
ar9285_ant_comb_scan: main: 61, alt: 22, rx_ant_conf: 0, main_ant_conf: 2
ar9285_ant_comb_scan: main: 61, alt: 22, rx_ant_conf: 0, main_ant_conf: 1
Here, an iperf TCP from STA (AR9285) to AP (tplink 11g wifi+adsl device) is around 25mbit. An AR2427 (AR9285 - 11n bits) gets around 30mbit; figuring that difference out can come later.
This matches the RSSI seen in the primary channel of ~ 30; (the hardware reports RSSI in 2* units.)
Then after some packet samples:
ar9285_ant_comb_scan: lna_conf: 2 -> 1
ar9285_ant_comb_scan: main_lna_conf: 1 -> 2
ar9285_ant_comb_scan: fast_div_bias: 2 -> 0
After that, the RSSI drops significantly on the main channel and is raised on the alt channel:
ar9285_ant_comb_scan: main: 47, alt: 41, rx_ant_conf: 0, main_ant_conf: 1
ar9285_ant_comb_scan: main: 45, alt: 41, rx_ant_conf: 0, main_ant_conf: 2
ar9285_ant_comb_scan: main: 45, alt: 41, rx_ant_conf: 0, main_ant_conf: 0
At this point, the iperf performance drops below 15mbit.
There also seems to be some invalid RSSI's creeping up, eg:
ar9285_ant_comb_scan: main: 9, alt: -90, rx_ant_conf: 2, main_ant_conf: 3
ar9285_ant_comb_scan: main: 46, alt: -103, rx_ant_conf: 3, main_ant_conf: 2
Fix: Patch attached with submission follows:
How-To-Repeat: I'm not sure if this is specific to my card and netbook/antenna or not; I'll do some further investigation to see what the root causes are.
But the diversity algorithm shouldn't make a poor antenna setup behave worse.. ?
I've disabled the diversity combining algorithm for now. HEAD works
fine now without it - cards that support fast diversity simply leave
it enabled by default (and the hardware does it) but without the
software changing the LNA/gain table/diversity bias configuration.
I think the main/alt logic is mis-classifying packets. I'll do some
further digging and reimplement things before I re-enable it.
For bugs that match the following
- Status Is In progress
- Untouched since 2018-01-01.
- Affects Base System OR Documentation
Reset to open status.
I did a quick pass but if you are getting this email it might be worthwhile to double check to see if this bug ought to be closed.