linux-kernel - Re: [patch update] PM: Introduce core framework for run-time PM of I/O devices

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Date:	Mon, 15 Jun 2009 17:08:56 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Oliver Neukum <oliver@...kum.org>, Magnus Damm <damm@...l.co.jp>,
	<linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>, Greg KH <gregkh@...e.de>
Subject: Re: [patch update] PM: Introduce core framework for run-time PM of
 I/O devices

On Mon, 15 Jun 2009, Rafael J. Wysocki wrote:

> On Sunday 14 June 2009, Rafael J. Wysocki wrote:
> > On Sunday 14 June 2009, Rafael J. Wysocki wrote:
> > > Hi,
> > > 
> > > Below is the current version of my "run-time PM for I/O devices" patch.
> > > 
> > > I've done my best to address the comments received during the recent
> > > discussions, but at the same time I've tried to make the patch only contain
> > > the most essential things.  For this reason, for example, the sysfs interface
> > > is not there and it's going to be added in a separate patch.
> > > 
> > > Please let me know if you want me to change anything in this patch or to add
> > > anything new to it.  [Magnus, I remember you wanted something like
> > > ->runtime_wakeup() along with ->runtime_idle(), but I'm not sure it's really
> > > necessary.  Please let me know if you have any particular usage scenario for
> > > it.]
> 
> Appended is an update of the patch addressing the today's comments from Magnus.

This is really looking very good.  I'll do a more detailed review
later.  (In particular, I have not checked the details of the rather
intricate state machine transitions.)  For now, a couple of things 
struck my eye:

Shouldn't the calls to complete() really be complete_all()?  There
might be more than one thread waiting for a suspend or resume callback
to finish.

Since pm_runtime_resume() takes care of powering up the parent, there's 
no need for pm_request_resume() to worry about it also.

The documentation should mention that the runtime_suspend method is 
supposed to enable remote wakeup if it as available and if 
device_may_wakeup(dev) is true.

Alan Stern

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