linux-kernel - Re: [PATCH] PM: Introduce core framework for run-time PM of I/O devices (rev. 3)

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Message-Id: <200906240208.23482.rjw@sisk.pl>
Date:	Wed, 24 Jun 2009 02:08:22 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-pm@...ts.linux-foundation.org,
	Oliver Neukum <oliver@...kum.org>,
	Magnus Damm <magnus.damm@...il.com>,
	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>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] PM: Introduce core framework for run-time PM of I/O devices (rev. 3)

On Tuesday 23 June 2009, Alan Stern wrote:
> On Tue, 23 Jun 2009, Rafael J. Wysocki wrote:
> 
> > Hi,
> > 
> > Below is a new revision of the patch introducing the run-time PM framework.
> > 
> > The most visible changes from the last version:
> > 
> > * I realized that if child_count is atomic, we can drop the parent locking from
> >   all of the functions, so I did that.
> > 
> > * Introduced pm_runtime_put() that decrements the resume counter and queues
> >   up an idle notification if the counter went down to 0 (and wasn't 0 previously).
> >   Using asynchronous notification makes it possible to call pm_runtime_put()
> >   from interrupt context, if necessary.
> > 
> > * Changed the meaning of the RPM_WAKE bit slightly (it is now also used for
> >   disabling run-time PM for a device along with the resume counter).
> > 
> > Please let me know if I've overlooked anything. :-)
> 
> This first thing to strike me was that you moved the idle notifications 
> into the workqueue.

Yes, I did.
 
> Is that really needed?  Would we be better off just make the idle
> callbacks directly from pm_runtime_put?  They would run in whatever
> context the driver happened to be in at the time.
> 
> It's not clear exactly how much work the idle callbacks will need to 
> do, but it seems likely that they won't have to do too much more than 
> call pm_request_suspend.  And of course, that can be done in_interrupt.

I just don't want to put any constraints on the implementation of
->runtime_idle().  The requirement that it be suitable for calling from
interrupt context may be quite inconvenient for some drivers and I'm afraid
they may have problems with meeting it.

Best,
Rafael
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