linux-kernel - Re: ath9k becon loss messages

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Date:	Mon, 6 Apr 2009 12:51:10 +0200
From:	Helmut Schaa <helmut.schaa@...glemail.com>
To:	Kalle Valo <kalle.valo@....fi>
Cc:	Michael Buesch <mb@...sch.de>,
	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Sujith <Sujith.Manoharan@...eros.com>,
	wireless <linux-wireless@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: ath9k becon loss messages

Am Montag, 6. April 2009 schrieb Kalle Valo:
> Michael Buesch <mb@...sch.de> writes:
> 
> >> NetworkManager typically scans every 120 seconds and I can also trigger
> >> the messages by a manual scan with iwlist. I did not dig any further but
> >> the messages seem to appear right at the end of the scan. Tried with iwlagn
> >> and both sw_scan and hw_scan.
> >
> > Yeah OK. While scanning it's expected to lose some frames.
> >
> > However, the driver should probably protect against this by using the
> > scan notification callbacks. It could disable beacon-loss reporting
> > while scanning.
> 
> That case is already covered. In sw_scan mac80211 will disable power
> save and hence beacon filter is also disabled.

Ok, that explains why the beacon loss is first detected after the scan
finished.

> But ath9k nor iwlwifi don't support beacon filtering and this is a
> problem in mac80211. We need to disable the beacon loss check in
> mac80211, most probably by stopping the associated timer whenever
> scanning.

Yeah, but the first execution of the timer will then also detect
beacon loss:

1006   if (!((local->hw.flags & IEEE80211_HW_BEACON_FILTER) &&
1007         (local->hw.conf.flags & IEEE80211_CONF_PS)) &&
1008       time_after(jiffies,
1009            ifmgd->last_beacon + IEEE80211_MONITORING_INTERVAL)) {

If the scan took longer then IEEE80211_MONITORING_INTERVAL (=2 sec) this
condition will apply just after the scan finished. Maybe this issue could be
avoided by making the beacon loss detection smarter then just checking if no
beacon was received within the last two seconds.

Helmut
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