linux-kernel - Re: [PATCH 2/5] drivercore: Add driver probe deferral mechanism

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Message-ID: <Pine.LNX.4.44L0.1110131202350.2026-100000@iolanthe.rowland.org>
Date:	Thu, 13 Oct 2011 12:04:25 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <tom.leiming@...il.com>
cc:	Grant Likely <grant.likely@...retlab.ca>,
	Andrei Warkentin <awarkentin@...are.com>,
	Greg KH <greg@...ah.com>, Dilan Lee <dilee@...dia.com>,
	"G, Manjunath Kondaiah" <manjugk@...com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	<linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Josh Triplett <josh@...htriplett.org>, <Manjunath@...per.es>,
	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Linux PM List <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH 2/5] drivercore: Add driver probe deferral mechanism

On Thu, 13 Oct 2011, Ming Lei wrote:

> Hi,
> 
> On Thu, Oct 13, 2011 at 10:31 PM, Alan Stern <stern@...land.harvard.edu>
> >> Maybe we should understand the correct model of the ordering constraints
> >> for the multiple device dependancies first, could you give a description or
> >> some examples about it?
> >
> > The requirement is that devices must be capable of resuming in the
> > order given by dpm_list, and they must be capable of suspending in
> > the reverse order.
> >
> > Therefore if device A can't work unless device B is functional, then B
> > must come before A in dpm_list.
> 
> If all devices can support async suspend and resume correctly, looks like
> the device order given by dpm_list is not needed any longer, doesn't it?

It _is_ needed, because the user can disable async suspend/resume via 
/sys/power/pm_async.

Also, not all devices do support async suspend/resume.

Alan Stern

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