linux-kernel - RE: [PATCH V7 4/9] wifi: mac80211: Add support for ACPI WBRF

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Date:   Tue, 25 Jul 2023 10:38:22 +0000
From:   "Quan, Evan" <Evan.Quan@....com>
To:     "Limonciello, Mario" <Mario.Limonciello@....com>,
        Andrew Lunn <andrew@...n.ch>
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Subject: RE: [PATCH V7 4/9] wifi: mac80211: Add support for ACPI WBRF

[AMD Official Use Only - General]

> -----Original Message-----
> From: Limonciello, Mario <Mario.Limonciello@....com>
> Sent: Monday, July 24, 2023 9:41 PM
> To: Andrew Lunn <andrew@...n.ch>; Quan, Evan <Evan.Quan@....com>
> Cc: rafael@...nel.org; lenb@...nel.org; Deucher, Alexander
> <Alexander.Deucher@....com>; Koenig, Christian
> <Christian.Koenig@....com>; Pan, Xinhui <Xinhui.Pan@....com>;
> airlied@...il.com; daniel@...ll.ch; johannes@...solutions.net;
> davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> pabeni@...hat.com; mdaenzer@...hat.com;
> maarten.lankhorst@...ux.intel.com; tzimmermann@...e.de;
> hdegoede@...hat.com; jingyuwang_vip@....com; Lazar, Lijo
> <Lijo.Lazar@....com>; jim.cromie@...il.com; bellosilicio@...il.com;
> andrealmeid@...lia.com; trix@...hat.com; jsg@....id.au; arnd@...db.de;
> linux-kernel@...r.kernel.org; linux-acpi@...r.kernel.org; amd-
> gfx@...ts.freedesktop.org; dri-devel@...ts.freedesktop.org; linux-
> wireless@...r.kernel.org; netdev@...r.kernel.org
> Subject: Re: [PATCH V7 4/9] wifi: mac80211: Add support for ACPI WBRF
>
> 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.
Yes, exactly.