Re: [PATCH V7 4/9] wifi: mac80211: Add support for ACPI WBRF

[Limonciello, Mario]

On 7/24/2023 04:22, Andrew Lunn wrote:
> > @@ -1395,6 +1395,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> >   	debugfs_hw_add(local);
> >   	rate_control_add_debugfs(local);
> >   
> > +	ieee80211_check_wbrf_support(local);
> > +
> >   	rtnl_lock();
> >   	wiphy_lock(hw->wiphy);
> >   
>
> > +void ieee80211_check_wbrf_support(struct ieee80211_local *local)
> > +{
> > +	struct wiphy *wiphy = local->hw.wiphy;
> > +	struct device *dev;
> > +
> > +	if (!wiphy)
> > +		return;
> > +
> > +	dev = wiphy->dev.parent;
> > +	if (!dev)
> > +		return;
> > +
> > +	local->wbrf_supported = wbrf_supported_producer(dev);
> > +	dev_dbg(dev, "WBRF is %s supported\n",
> > +		local->wbrf_supported ? "" : "not");
> > +}
>
> This seems wrong. wbrf_supported_producer() is about "Should this
> device report the frequencies it is using?" The answer to that depends
> on a combination of: Are there consumers registered with the core, and
> is the policy set so WBRF should take actions. >
> The problem here is, you have no idea of the probe order. It could be
> this device probes before others, so wbrf_supported_producer() reports
> false, but a few second later would report true, once other devices
> have probed.
>
> It should be an inexpensive call into the core, so can be made every
> time the channel changes. All the core needs to do is check if the
> list of consumers is empty, and if not, check a Boolean policy value.
>
>       Andrew

No, it's not a combination of whether consumers are registered with the 
core.  If a consumer probes later it needs to know the current in use 
frequencies too.

The reason is because of this sequence of events:
1) Producer probes.
2) Producer selects a frequency.
3) Consumer probes.
4) Producer stays at same frequency.

If the producer doesn't notify the frequency because a consumer isn't 
yet loaded then the consumer won't be able to get the current frequency.