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Date:   Mon, 24 Jul 2023 08:40:33 -0500
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Subject: Re: [PATCH V7 4/9] wifi: mac80211: Add support for ACPI WBRF
To:     Andrew Lunn <andrew@lunn.ch>, Evan Quan <evan.quan@amd.com>
Cc:     rafael@kernel.org, lenb@kernel.org, Alexander.Deucher@amd.com,
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References: <20230719090020.2716892-1-evan.quan@amd.com>
 <20230719090020.2716892-5-evan.quan@amd.com>
 <9b1f45f9-02a3-4c03-b9d5-cc3b9ab3a058@lunn.ch>
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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.