linux-kernel - Re: [RFC][PATCH] PM: Introduce core framework for run-time PM of I/O devices (rev. 8)

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Message-Id: <200907082329.51795.rjw@sisk.pl>
Date:	Wed, 8 Jul 2009 23:29:50 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Magnus Damm <magnus.damm@...il.com>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	Greg KH <gregkh@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC][PATCH] PM: Introduce core framework for run-time PM of I/O devices (rev. 8)

On Wednesday 08 July 2009, Alan Stern wrote:
> On Wed, 8 Jul 2009, Rafael J. Wysocki wrote:
> 
> > > I thought you wanted to avoid this sort of complication.
> > 
> > I did, but there might be some benefits.  For example, the timer and the work
> > structure provided by dev.power can be used for scheduling such operations
> > if they are defined at the core level.
> > 
> > Suppose your device has 3 low power states D1 - D3 (like PCI) and you want it
> > to go into D1 first, then, after a delay, to D2 and finally, again after a
> > delay, to D3.  Of course, if there's a resume in the meantime, it should cancel
> > whichever transition is in progress.
> > 
> > pm_runtime_suspend() can be used for the first transition, but the bus type or
> > driver will have to provide its own mechanics for going down to D2 and D3,
> > which must be synchronized with its ->runtime_resume().  That might be tricky
> > and the core already has what's necessary (well, almost).
> 
> Maybe we can provide a way for drivers to set up their own timer 
> callback or work routine for use while the status is RPM_SUSPENDED.

Agreed.

Anyway, I don't think it's really necessary in the Magnus' usage case, as
you pointed out earlier in this thread, so I think we can consider it as
something to add in future.

The current patch is already more that 1200 lines and there's some
documentation to add, so I wouldn't like to make it any bigger. :-)

Best,
Rafael
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