linux-kernel - Re: [PATCH] platform/x86: acer-wmi: improve platform profile handling

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Message-ID: <20e3ac66-b040-49a9-ab00-0adcfdaed2ff@gmx.de>
Date: Fri, 3 Jan 2025 22:07:57 +0100
From: Armin Wolf <W_Armin@....de>
To: Hridesh MG <hridesh699@...il.com>, Kurt Borja <kuurtb@...il.com>
Cc: "Lee, Chun-Yi" <jlee@...e.com>, Hans de Goede <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
 Shuah Khan <skhan@...uxfoundation.org>, onenowy@...il.com
Subject: Re: [PATCH] platform/x86: acer-wmi: improve platform profile handling

Am 03.01.25 um 20:52 schrieb Hridesh MG:

>> Do you perhaps know if users expect a thermal profile change on AC
>> connect/disconnect events on Windows? This would solve this discussion
>> [1].
> Yep, there is a profile change on AC disconnect on Windows.
> Specifically, it forces the balanced platform profile and returns to
> the last active profile on replugging (the UI disallows changing of
> profiles when disconnected but it is possible via WMI)
>
>>  From my testing, what I've found out is that even if we don't handle
>> on_AC, the profile is still set but the hardware will not put the
>> changes into effect until we plug in AC.
> I did some more testing and I was a bit mistaken in the way it works.
> While the system is unplugged it will still apply the three different
> profiles (as evident by the differing fan speeds) but the CPU will
> aggressively throttle under stress, placing an upper limit on the
> maximum clock rate, this limit is lifted upon plugging in AC.

That is some very important information right here. The platform-profile documentation states:

	"Specifically when selecting a high performance profile the actual achieved
	 performance may be limited by various factors such as: the heat generated
	 by other components, room temperature, free air flow at the bottom of a
	 laptop, etc. It is explicitly NOT a goal of this API to let userspace know
	 about any sub-optimal conditions which are impeding reaching the requested
	 performance level."

I think the AC handling is unnecessary in this case as the hardware seems to accept different profiles
even when not running on AC. This would simplify the platform profile cycling inside the driver and
allow us to use platform_profile_cycle().

I wonder if this special behavior of the acer-wmi driver is documented somewhere. I am asking this since
this has a great potential to confuse users.

Thanks,
Armin Wolf

>
> --
> Thanks,
> Hridesh MG