Message-ID: <1360767542.8868.20.camel@jlt4.sipsolutions.net> (sfid-20130213_155913_750414_C452071F)
Subject: Re: [RFCv2 2/3] mac80211: mesh power save doze scheduling
From: Johannes Berg <johannes@sipsolutions.net>
To: Marco Porsch <marco@cozybit.com>
Cc: mcgrof@qca.qualcomm.com, jouni@qca.qualcomm.com,
	vthiagar@qca.qualcomm.com, senthilb@qca.qualcomm.com,
	linux-wireless@vger.kernel.org, devel@lists.open80211s.org,
	ath9k-devel@lists.ath9k.org
Date: Wed, 13 Feb 2013 15:59:02 +0100
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On Mon, 2013-02-11 at 13:03 +0100, Marco Porsch wrote:
> On 02/08/2013 10:57 PM, Johannes Berg wrote:
> > On Fri, 2013-02-08 at 11:09 +0100, Marco Porsch wrote:
> >
> >>>> For mesh Awake Windows wakeup on SWBA (beacon_get_tim) and start
> >>>> a timer which triggers a doze call on expiry.
> >>>
> >>> That seems questionable -- drivers are not required to request each
> >>> beacon. I know you only want to make it work on ath9k, but I don't think
> >>> "stretching" the API, without even documenting it, is a good idea.
> >>
> >> Currently, we already use ieee80211_beacon_get_tim as time reference for
> >> mesh sync's adjust_tbtt. And, as far as I know, all mesh-capable drivers
> >> use the call for each and every beacon.
> >
> > Oops, why did I miss that before? :-)
> >
> >> So what would you recommend: keep using beacon_get and adding
> >> documentation - or - creating an exported callback for awake_window_start?
> >
> > I guess you could add it... However, I don't really fully understand.
> > There's no guarantee that fetching the beacon is done anywhere close to
> > TBTT? Or does ath9k happen to do it just after TXing a beacon? You're
> > encoding quite a lot of ath9k-specific assumptions here it seems?
> 
> I think the assumption is currently correct for ath5k, ath9k, ath9k_htc, 
> carl9170 and rt2800 (that's as far as I checked). All of these fetch a 
> beacon on SWBA/PRETBTT interrupt (more or less) immediately before TBTT.

It's still pretty bad to make that assumption implicitly -- I think you
should at least document it as a big todo item :)

johannes