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

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Date:	Thu, 13 Oct 2011 10:31:45 -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:

> >> Inside device_add(), device_pm_add is called before bus_probe_device,
> >> so the patch can't change the device order in pm list, and just change
> >> the driver probe order.
> >
> > That's the way it works now, but can it be reworked?  It would be
> 
> IMO, it depends on what shape you plan to rework.  Currently, the
> deferred probe may found a resource dependency, but I am not sure
> that pm dependency is same with the resource dependency found
> during probe.
> 
> > possible to adjust the list order after successful probe.  However,
> > I'm not clear on the ordering rules for the dpm_list.  Right now it is
> > explicitly ordered to have parents before children, but as already
> > expressed, that doesn't accurately represent ordering constraints for
> > multiple device dependancies.
> 
> 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.

Alan Stern

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