linux-kernel - Re: [PATCH v2 3/3] ACPI / sleep: EC-based wakeup from suspend-to-idle on recent Dell systems

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Date:   Tue, 20 Jun 2017 10:00:18 +0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Darren Hart <dvhart@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Mario Limonciello <mario.limonciello@...l.com>,
        Tom Lanyon <tom@...shoeco.com>,
        Jérôme de Bretagne 
        <jerome.debretagne@...il.com>
Subject: Re: [PATCH v2 3/3] ACPI / sleep: EC-based wakeup from suspend-to-idle
 on recent Dell systems

On Tue, Jun 20, 2017 at 9:13 AM, Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> My understanding is that Windows uses the ACPI_FADT_LOW_POWER_S0 flag.
> It generally enables non-S3 suspend/resume when this flag is set and
> it doesn't touch S3 then.  Keeping the EC GPE (and other GPEs for that
> matter) enabled over suspend/resume is part of that if my
> understanding is correct.
>
> During suspend we generally disable all GPEs that are not expected to
> generate wakeup events in order to avoid spurious wakeups, but we can
> try to keep them enabled if ACPI_FADT_LOW_POWER_S0 is set.  That will
> reduce the ugliness, but the cost may be more energy used while
> suspended on some systems.

I think trying to do something similar to what windows does is likely
the right thing, since that is (sadly) the only thing that tends to
get extensive testing still.

Of course, different versions of Windows then probably do different
things, but I guess ACPI_FADT_LOW_POWER_S0 ends up being a good sign
of "new machine designed for windows 10", so it's probably a good
thing to trigger that behavior on.

So I suspect it's worth testing, particularly if we're going to be in
the situation that a lot of machines are going to do this going
forward (ie the "all Dell" may end up being more than just Dell too?
Dell usually doesn't do particularly odd and out-of-the-norm design
choices like some vendors do).

              Linus