linux-kernel - [PATCH 0/3] PM / Domains: Fix device stop and domain power off governor functions, take 2

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Date:	Wed, 25 Apr 2012 21:28:32 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linux PM list <linux-pm@...r.kernel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Kevin Hilman <khilman@...com>,
	Magnus Damm <magnus.damm@...il.com>, linux-sh@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	markgross@...gnar.org, Jean Pihet <j-pihet@...com>,
	Simon Horman <horms@...ge.net.au>
Subject: [PATCH 0/3] PM / Domains: Fix device stop and domain power off governor functions, take 2

Hi all,

On Tuesday, April 24, 2012, Rafael J. Wysocki wrote:
> Hi all,
> 
> It turns out that the PM domains device stop and domain power off governor
> functions I invented some time ago don't really make sense, because they
> should only decide whether or not the resulting low-power state will be
> too deep and that only depends on latencies.  In particular, the time
> when devices have been suspended doesn't really matter here, so the
> results returned by those functions shouldn't depend on it either (as it
> shouldn't depend on any "break even" values that only make sense when we
> know how much time in advance the device is going to be used, but this
> information is not related to the PM QoS latency constraint).
> 
> If this functions are fixed (patches [1/3] and [2/3]), then some ugly
> computations can be removed from rpm_suspend() and other places and the
> whole framework can be simplified quite a bit (patch [3/3]).

I noticed a few problems with the patches sent yesterday.  Most importantly:

* dev_pm_qos_read_value() should be used rather than its unlocked counterpart.
* All children of the device have to be taken into account, not only those
  belonging to generic PM domains.
* default_power_down_ok() should take restore_state_latency_ns into account.
* default_power_down_ok() should not assume that default_stop_ok() will always
  be called before it (the domain may choose to use a different device stop
  governor function in principle).
* rpm_resume() still should check the devices PM QoS constraint and return
  error code if the value is negative (which means never suspend).

Updated patches follow.

Thanks,
Rafael

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