Subject: Re: Power saving on mac80211
From: Johannes Berg <johannes@sipsolutions.net>
To: Kalle Valo <kalle.valo@nokia.com>
Cc: "Luis R. Rodriguez" <mcgrof@gmail.com>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Zhu Yi <yi.zhu@intel.com>
In-Reply-To: <871vyc7st7.fsf@nokia.com>
References: <43e72e890810171810t1c65642g998db601cfe2a390@mail.gmail.com>
	 <87bpxh6t1n.fsf@nokia.com> <87y70l59p4.fsf@nokia.com>
	 <1224412006.6324.45.camel@johannes.berg>  <871vyc7st7.fsf@nokia.com>
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Date: Sun, 19 Oct 2008 18:48:05 +0200
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On Sun, 2008-10-19 at 14:00 +0300, Kalle Valo wrote:

> > Then add a new flag to mac80211 hw description that says "driver will
> > watch beacons". This means that the code above that rearms the timer fo=
r
> > the future 'nothing from AP' check is skipped.
>=20
> I will. I need to check that if the "firmware beacon watch" is enabled
> only when PSM is enabled. If it is, we might have to make the flag
> dynamic.

IIRC it's a separate flag.

> > Also add a way for mac80211 to tell the driver after how many beacons
> > (or calculate the timeout in ms, it's convertible) it should tell
> > mac80211 about the situation. Finally, to make it possible to have the
> > driver tell mac80211, extend the MLME callback (ieee80211_notify_mac)
>=20
> The beacon filtering in stlc4560 works so that a beacon is passed to
> the host only when the TIM bit for the AID is set.

There's also a beacon checksum feature which we might want to enable,
just in case the AP ever changes QoS parameters etc.

>  There isn't any
> timeout for delivering beacons to the host, if the data path is idle
> for 24 hours, mac80211 will not receive any beacons for the 24 hours.
> I don't see why we need a timeout here.

Right. But we need to program the chip to tell the chip "hey please tell
me if you haven't seen a beacon in X seconds".

> I believe that there's also a feature in stlc4560 that the driver can
> provide a checksum of the beacon and the firmware will send the beacon
> if checksum doesn't match. But I don't yet know how that works in
> practise.

It seems to be a firmware feature, first beacon from the BSS the
firmware computes the checksum, and if it changes it lets the beacon go
through and re-computes the checksum, so you see all beacon changes.
Maybe it excludes the TIM. I think we want this for when the QoS
parameters or something else changes.

johannes

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