2016-01-27 2:46 GMT-05:00 Grumbach, Emmanuel <emmanuel.grumbach@xxxxxxxxx>: >> Hi >> >> 2016-01-26 3:28 GMT-05:00 Grumbach, Emmanuel >> <emmanuel.grumbach@xxxxxxxxx>: >> > >> > >> > On 01/26/2016 12:20 AM, Nikolay Martynov wrote: >> >> It looks like sometimes firmware returns zero for chain noise and >> >> signal during calibration period. This seems to be a known problem >> >> and current implementation accounts for this by ignoring invalid data >> >> when all chains return zero signal and noise. >> >> >> >> The problem is that sometimes firmware returns zero for only one >> >> chain for some (not all) beacons used for calibration. This leads to >> >> perfectly valid chains be disabled and may cause invalid gain settings. >> >> For example this is calibration data taken on laptop with Intel 6300 >> >> card with all three antennas attached: >> >> >> >> active_chains: 3 >> >> chain_noise_a: 312 >> >> chain_noise_b: 297 >> >> chain_noise_c: 0 >> >> chain_signal_a: 549 >> >> chain_signal_b: 513 >> >> chain_signal_c: 0 >> >> beacon_count: 16 >> >> disconn_array: 0 0 1 >> >> delta_gain_code: 4 0 0 >> >> radio_write: 1 >> >> state: 3 >> >> >> >> This patch changes statistics gathering to make sure that zero noise >> >> results are ignored for valid rx chains. The rationale being that >> >> even if anntenna is not connected we should be able to see non zero >> >> noise if rx chain is present. >> > >> > But then the firmware will continue to send zero for signal and this >> > will impact lots of flows like roaming. If the driver allows the >> > firmware to use that antenna, the firmware may use this antenna for >> > scanning and roaming will be broken. >> > This seems to be a bug in the firmware, but there isn't much I can do >> > about it. >> > Sorry, I have to NACK this patch. >> >> Could you please elaborate on how this patch would affect roaming or other >> things. As far as I can see this patch doesn't change much behavior apart >> from ignoring invalid values from firmware. >> Disconnected antennas still get disabled (as before) connected antennas still >> work (more often than before). So I'm not sure I can see how this patch >> would change what firmware does at all. I really hope you could find a >> moment and explain this. >> > > What you are saying here is that there is a bug in the firmware which makes it report wrong > values for one of the antennas. But when you will have this antenna enabled (with your patch), > the firmware will keep sending bad signal / noise values for it. If the driver allows the firmware > to use this antenna (after your patch), the firmware will choose this antenna to receive beacons > or to scan. Then, the driver will look at the beacons' rssi (which will be wrong) and it will think that > an AP which is very close is in fact far away. > No. That is not correct, I think. What I'm saying is that sometimes (not always) firmware is sending 0 (exactly 0) for signal and noise for some (or all) chains. The case when all chains get 0 seem to be a known problem: it is worked around in iwl_find_disconn_antenna. The case when only one chain gets zero is not currently handled. And just to clarify - all chains are affected by this problem, it's not like one specific chain is broken in some way and gets zero. So both of the cards I have may be running with 3 chains or with 2 chains depending on how lucky I'm during initial scan. It's just firmware that has a bug that sometimes returns zero for chain 1, sometimes for chain 2, and sometimes for all of them. So currently driver is already enabling chains for which we may get zero later for rssi (presumably this is true) if it gets non zero during scan for first 16 beacons. Moreover, if it gets non-zero for 15 out of 16 beacons the chain is not disabled but gain values are wrong because of this - and one chain would be amplifying things more than it should - this is currently happening to the best of my understanding. So my patch filters out results that we know are bad to account for this firmware bug. With this patch all chains with antenna attached get signal and noise reading - suggesting that firmware actually returns zero only some times and after several retries we get reasonable statistics. It looks like there are some 'transitioning' processes in firmware and if we out-wait them we get good statistics. I'm not sure I see how this patch makes anything more worse than they currently already are. Currently it is already (presumably) possible to get wrong rssi reading because chain that may have been enabled during first scan may get zeros later. All my patch does is to enable all equivalently good (or bad) antennas, instead of two equivalently good (or bad) as current code does. Does this explanation make any sense? Is it flawed in some way? If patch in it's current state seems too controversial would patch that enables this check if some module parameter is set (and it is not set my default) be more acceptable? Thanks! -- Martynov Nikolay. Email: mar.kolya@xxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
