linux-kernel - Re: [patch update 3] PM: Introduce core framework for run-time PM of I/O devices

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Date:	Tue, 23 Jun 2009 13:02:15 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Oliver Neukum <oliver@...kum.org>,
	Magnus Damm <magnus.damm@...il.com>,
	<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 3] PM: Introduce core framework for run-time PM
 of I/O devices

On Mon, 22 Jun 2009, Rafael J. Wysocki wrote:

> > And of course, synchronous pm_runtime_resume should always increment the 
> > counter.
> 
> Sure.

Now that I've thought about it some more, I decided that we might want
to be more flexible.  Without subjecting you to the entire line of
reasoning, let's just say that I'm starting to wonder whether it's such
a good idea to tie the counter increments to the PM core runtime resume
calls at all.

Maybe it would be better (easier to use, less constraining) to require
the runtime_resume callback to do its own pm_runtime_get.  That way the
driver would be entirely responsible for managing the usage counter;
the PM core wouldn't be involved.  pm_runtime_get would simply
increment the counter, so it could be used even in interrupt context.  
At the moment, I don't see any need for it to queue an autoresume
request if the device happens to be suspended.

Something like this was probably your intention all along.  :-)

Alan Stern

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