linux-kernel - Re: [RFC 2/2] platform/x86/amd: pmf: Add manual control support

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Message-ID: 
 <CAGwozwGXh1RV96hvSEd3HQoKGY+DeRPrhcKMxJUu7STRZURsmg@mail.gmail.com>
Date: Thu, 26 Sep 2024 10:52:24 +0200
From: Antheas Kapenekakis <lkml@...heas.dev>
To: Mario Limonciello <superm1@...nel.org>
Cc: Shyam Sundar S K <Shyam-sundar.S-k@....com>,
 "Rafael J . Wysocki" <rafael@...nel.org>,
	Hans de Goede <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	"Luke D . Jones" <luke@...nes.dev>, Mark Pearson <mpearson-lenovo@...ebb.ca>,
	"open list:AMD PMF DRIVER" <platform-driver-x86@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:ACPI" <linux-acpi@...r.kernel.org>,
 "Derek J . Clark" <derekjohn.clark@...il.com>,
	me@...egospodneti.ch, Denis Benato <benato.denis96@...il.com>,
	Mario Limonciello <mario.limonciello@....com>
Subject: Re: [RFC 2/2] platform/x86/amd: pmf: Add manual control support

Hi Mario,

It is fine to require a module parameter for turning on custom profiles.

However, distributions such as Bazzite use per-device kernel
parameters, which, while user accessible, will not be modified by the
user for 95% of use-cases. In fact, the Bazzite update system manages
the kernel parameters of devices automatically.

What this would mean in practice is that for devices where this custom
control may be used, the module parameter will be set globally for all
of them and taint their kernels.

Instead, only taint the kernel when entering custom mode. If combined
with something such as `custom_mode_choices`, only taint the kernel if
`amd-pmf-user` is selected after that.

> +{
> +       add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
> +       pr_crit("Manual PMF control is enabled, please disable it before "
> +               "reporting any bugs unrelated to PMF.\n");
> +}

"Manual PMF control is enabled. If the device supports other ways of
thermal management, please use those before reporting any bugs
unrelated to PMF. If not, only if setting TDP is required for testing
(e.g., under load in specific thermal conditions), proceed with the
understanding that this module may cause interference, especially with
the amd-gpu driver, the suspend process, and, if the parameters are
out of spec, general stability of the system."

Antheas