linux-kernel - Re: [PATCH v1] platform/x86: intel_pmc_core: promote S0ix failure warn() to WARN()

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Date:   Mon, 31 Oct 2022 21:38:42 -0400
From:   Sven van Ashbrook <svenva@...omium.org>
To:     "Limonciello, Mario" <Mario.Limonciello@....com>
Cc:     Rajneesh Bhardwaj <irenic.rajneesh@...il.com>,
        Hans de Goede <hdegoede@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "S-k, Shyam-sundar" <Shyam-sundar.S-k@....com>,
        "rrangel@...omium.org" <rrangel@...omium.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>,
        Rafael J Wysocki <rjw@...ysocki.net>,
        Rajat Jain <rajatja@...gle.com>,
        David E Box <david.e.box@...el.com>,
        Mark Gross <markgross@...nel.org>
Subject: Re: [PATCH v1] platform/x86: intel_pmc_core: promote S0ix failure
 warn() to WARN()

On Mon, Oct 31, 2022 at 3:39 PM Limonciello, Mario
<Mario.Limonciello@....com> wrote:
>
> Just thinking about it a little bit more, it could be a lot nicer to have something like:
>
> /sys/power/suspend_stats/last_hw_deepest_state

While I agree that reporting through a framework is generally better
than getting infrastructure to grep for specific strings, I believe
that a simple sysfs file is probably too simplistic.

1. We need more sophisticated reporting than just last_hw_deepest_state:

- sometimes the system enters the deep state we want, yet after a
while moves back up and gets "stuck" in an intermediate state (below
S0). Or, the system enters the deep state we want, but moves back to
S0 after a time without apparent reason. These platform-dependent
failures are not so easily describable in a generic framework.

- ChromeOS in particular has multiple independent S0ix / S3 / s2idle
failure report sources. We have the kernel warning above; also our
Embedded Controller monitors suspend failure cases which the simple
kernel warning cannot catch, reported through a separate WARN_ONCE().

2. A simple sysfs file will need to be polled by the infrastructure
after every suspend; it would be preferable to have some signal or
callback which the infrastructure could register itself with.

The generic infrastructure to support this sounds like quite a bit of
work, and for what gain? Compared to simply matching a log string and
sending the whole dmesg if there's a match.

Is the light worth the candle?

Sven