Re: [PATCH] ath9k: ignore radar PHY errors when DFS is not enabled

[Zefir Kurtisi <zefir.kurtisi@neratec.com>]

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On 01/10/2015 05:26 PM, Simon Wunderlich wrote:
> On Friday 09 January 2015 19:57:37 Arend van Spriel wrote:
>> On 01/09/15 17:54, Simon Wunderlich wrote:
>>> Performing spectral scans on 5 GHz channels may result in PHY errors
>>> sent by the hardware, even if DFS support is not enabled in the driver
>>> (e.g. channel scanning or passive monitoring). In that case channels may
>>> falsely get marked as 'unusable'. To fix that, only process radar PHY
>>> errors when radar is explicitly enabled in the driver.
>>
>> Hi Simon,
>>
>> Not an ath9k expert, but I would think those channels would already be
>> marked as unusable, because DFS is disabled in the driver. Or does this
>> also affect 5G channels that do not require DFS.
>>
>> Regards,
>> Arend
> 
> Hey Arend,
> 
> maybe that was not really clear, but this is talking about the DFS state 
> "unusable". By default, channels are marked in DFS state "usable", and after 
> the clear channel assessment (which is done e.g. when starting AP mode) they 
> are marked as "available". As soon as radar is detected they are marked as 
> "unusable".
> 
> These DFS state changes should only happen while there is something operating 
> with radar enabled, e.g. AP mode. It should not happen if we just have monitor 
> mode or scan for channels. These channels should then stay in their previous 
> DFS state (e.g. 'usable'). This was borked and this patch tries to fix it. :)
> 
> Cheers,
>      Simon
> 
Hi,

the issue here is that DFS and spectral use the same PHY_ERROR reporting
mechanism, and the dfs module is still in its initial state prior the spectral
support was added. With that, feeding the dfs detector with PHY_ERROR frames
generated by spectral scanner might cause false radar detections.

I did not dig how the hw->conf.radar_enabled flag is set in monitor mode, but if
it is same as for master (i.e. set for DFS channels), then it would be a better
approach to prevent calling ath9k_dfs_process_phyerr() altogether from
ath9k_rx_skb_preprocess() if not set.

And while you're at that: slaves do not need to scan for radar, might be worth
checking if it makes sense to selectively disable radar detection in STA mode. I
am using attached private OpenWRT patch for that - which still would interfere
with spectral scanning. Generally, the PHY_ERROR processing should be reworked but
becomes quite complicated when you take into account special use-cases. Think of
radar events being treated differently depending on whether a master or a monitor
detected them (OC-CAC vs. ISM).


Cheers,
Zefir


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>From 089ab0d624d4b6f3a206ea8a81b4a3e061cf3edb Mon Sep 17 00:00:00 2001
From: Zefir Kurtisi <zefir.kurtisi@neratec.com>
Date: Thu, 30 Jan 2014 13:33:50 +0100
Subject: [PATCH] ath9k: do not enable radar pulse detection in STA mode

---
 drivers/net/wireless/ath/ath9k/recv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/wireless/ath/ath9k/recv.c
+++ b/drivers/net/wireless/ath/ath9k/recv.c
@@ -384,7 +384,7 @@ u32 ath_calcrxfilter(struct ath_softc *s
 		| ATH9K_RX_FILTER_MCAST;
 
 	/* if operating on a DFS channel, enable radar pulse detection */
-	if (sc->hw->conf.radar_enabled)
+	if (sc->hw->conf.radar_enabled && sc->sc_ah->opmode != NL80211_IFTYPE_STATION)
 		rfilt |= ATH9K_RX_FILTER_PHYRADAR | ATH9K_RX_FILTER_PHYERR;
 
 	spin_lock_bh(&sc->chan_lock);