linux-kernel - Re: [PATCH] ACPI: scan: Turn off unused power resources during initialization

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Message-ID: <CAJZ5v0iDofnMTO8-GkBMGeQJkr1hSKU_uihKR87xTT1zJ2J_MQ@mail.gmail.com>
Date:   Thu, 18 Mar 2021 12:07:16 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        David Box <david.e.box@...ux.intel.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH] ACPI: scan: Turn off unused power resources during initialization

On Wed, Mar 17, 2021 at 10:27 PM Paul Menzel <pmenzel@...gen.mpg.de> wrote:
>
> Dear Rafael,
>
>
> Am 17.03.21 um 17:49 schrieb Rafael J. Wysocki:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > It is reported that on certain platforms unused ACPI power resources
> > that have not been explicitly turned off prevent the platform from
> > reaching the lowest power state in suspend-to-idle which leads to
> > excessive power draw.
> >
> > For this reason, turn all of the unused ACPI power resources off
> > at the end of the initial namespace scan for devices in analogy with
> > resume from suspend-to-RAM.
> >
> > Reported-by: David Box <david.e.box@...ux.intel.com>
>
> Thank you for the patch. Could you please add more details to the commit
> message, saying what device this was on, and if there were some
> error/warning messages pointing to the problem?

The actual report is not public, so I cannot quote it.

In essence, there is a power resource in the affected system that
would be dedicated to a specific device, but that device is not
present in that variant of the platform.

However, the behavior introduced by this patch is generally mandated
by the spec and evidently depended on by firmware developers (see the
second paragraph in
https://uefi.org/specs/ACPI/6.4/07_Power_and_Performance_Mgmt/device-power-management-objects.html).