linux-kernel - Re: [PATCH 1/2] PM: docs: Describe high-level PM strategies and sleep states

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Date:   Sun, 20 Aug 2017 20:23:26 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Linux Documentation <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 1/2] PM: docs: Describe high-level PM strategies and
 sleep states

On Sun, Aug 20, 2017 at 06:05:05PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Reorganize the power management part of admin-guide by adding a
> description of major power management strategies supported by the
> kernel (system-wide and working-state power management) to it and
> dividing the rest of the material into the system-wide PM and
> working-state PM chapters.
> 
> On top of that, add a description of system sleep states to the
> system-wide PM chapter.

Found no typos and no factual inaccuracies, the only thing that
irritated me a bit was the part about "working state" power
management:

> +The other strategy, referred to as the
> +:doc:`working-state power management <working-state>`, is based on adjusting the
> +power states of individual hardware components of the system, as needed, in the
> +working state.  In consequence, if this strategy is in use, the working state
> +of the system usually does not correspond to any particular physical
> +configuration of it, but can be treated as a metastate covering a range of
> +different power states of the system in which the individual components of it
> +can be either ``active`` (in use) or ``inactive`` (idle).  If they are active,
> +they have to be in power states allowing them to process data and to be accessed
> +by software.  In turn, if they are inactive, they are expected to be in
> +low-power states in which they may not be accessible.
> +
> +If all of the system components are active, the system as a whole is regarded as
> +``runtime active`` and that situation typically corresponds to the maximum power
> +draw (or maximum energy usage) of it.  If all of them are inactive, the system
> +as a whole is regarded as ``runtime idle`` which may be very close to a sleep

The code uses the terms pm_runtime_active() and pm_runtime_suspended(),
not "runtime idle".  Taking the ->runtime_idle callback as guidance,
"runtime idle" would mean that a component is runtime active, but idling
and could thus be transitioned to runtime suspended state.  However above
it says that if it's idle, it's already "in low-power states and may
not be accessible".  For someone reading this it may be difficult to
reconcile it with the terminology used in the code.

Otherwise,
Reviewed-by: Lukas Wunner <lukas@...ner.de>

Thanks,

Lukas