Re: [RFC v2] mac80211: extend/document powersave API

[Johannes Berg <johannes@sipsolutions.net>]

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On Wed, 2009-01-07 at 17:49 +0200, Kalle Valo wrote:

> > + * First, it can support hardware that handles all powersaving by
> > + * itself, such hardware should simply set the %IEEE80211_HW_SUPPORTS_PS
> > + * hardware flag. In that case, it will be told about the desired
> > + * powersave mode regardless of association status, and the driver or
> > + * hardware must take care of enabling/disabling powersave depending on
> > + * the association status and TIM bit and send nullfunc frames by
> > + itself.
> 
> Actually I'm not aware of any hardware designs which enables and
> disables power save according to association status (modulo fullmac
> design, of course). Even iwlwifi, which I think has the most
> sophisticated power save support, requires the host to enable power
> save according to the association status. Hence I would like to have
> the power save enable/disable logic based on association status in
> mac80211.

Yeah, good point. But iwlwifi is confusing me ;) Since iwlwifi is the
only user, I'll clean that up along with cleaning up iwlwifi, would you
mind leaving it as-is, and I'll fix it in the short term?

> We already have this support in ieee80211_set_associated() 
> 
> [Reads the function again] 
> 
> Or, actually we had it. I think Vivek's patch changed the
> functionality. But anyway, it's very easy to add the support back.
> 
> The reason why I would like to have this in mac80211 is to avoid
> having duplicate bugs in different drivers and make the driver
> implementation easier.

Makes sense.

> > + * Additionally, such hardware may set the %IEEE80211_HW_SUPPORTS_DYNAMIC_PS
> > + * flag to indicate that it can support dynamic PS mode (see below).
> > + *
> > + * Other hardware designs cannot send nullfunc frames by themselves and
> > + * need to be told explicitly about powersave transitions depending on
> > + * association status, need software support for parsing the TIM bitmap
> > + * and can implement dynamic PS mode in software. This is also supported
> > + * by mac80211 by combining the %IEEE80211_HW_SUPPORTS_PS and
> > + * %IEEE80211_HW_PS_NULLFUNC_STACK flags.
> 
> stlc45xx (and p54spi) wakeup for multicast frames automatically, but
> ath5/9k need the host to do it. I think we will need a separate flag
> for that, but I can add it later.

Good point, we need to add that later.

> > @@ -858,8 +861,17 @@ static int ieee80211_ioctl_siwpower(stru
> >  	if (wrq->flags & ~(IW_POWER_MODE | IW_POWER_TIMEOUT))
> >  		return -EINVAL;
> >  
> > -	if (wrq->flags & IW_POWER_TIMEOUT)
> > +	if (wrq->flags & IW_POWER_TIMEOUT) {
> > +		/*
> > +		 * dynamic PS only supported if nullfunc handling in stack
> > +		 * or hardware supports dynamic PS itself
> > +		 */
> > +		if (!(local->hw.flags & IEEE80211_HW_SUPPORTS_DYNAMIC_PS) &&
> > +		    !(local->hw.flags & IEEE80211_HW_PS_NULLFUNC_STACK))
> > +			return -EOPNOTSUPP;
> > +
> >  		timeout = wrq->value / 1000;
> > +	}
> 
> Actually there are hardware designs which don't have dynamic power
> save but have null frame creation in firmware (and hence don't need
> IEEE80211_HW_PS_NULLFUNC_STACK). So IEEE80211_HW_SUPPORTS_DYNAMIC_PS
> and IEEE80211_HW_PS_NULLFUNC_STACK are not related to each other in
> any way. I suspect at76_usb is such design, but I need to recheck
> that.

But if they don't have dynps but nullfunc in firmware then we can't
support dynamic ps at all, can we?

> So I would like to implement this so that if
> IEEE80211_HW_SUPPORTS_DYNAMIC_PS is not set mac80211 will always use
> it's own timer, independent of IEEE80211_HW_PS_NULLFUNC_STACK. If you
> agree, I can create a separate patch for this.

Oh, I see now, so the firmware just creates the nullfunc whenever you
tell it to? bit strange, I guess.

johannes

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