linux-kernel - Re: [GIT PULL] On-demand device probing

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Message-ID: <Pine.LNX.4.44L0.1510201036290.1855-100000@iolanthe.rowland.org>
Date:	Tue, 20 Oct 2015 10:40:03 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Rob Herring <robh@...nel.org>
cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
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Subject: Re: [GIT PULL] On-demand device probing

On Tue, 20 Oct 2015, Rob Herring wrote:

> > The probe ordering is not the entire picture, though.
> >
> > Even if you get the probe ordering right, the problem is going to show up in
> > multiple other places: system suspend/resume, runtime PM, system shutdown,
> > unbinding of drivers.  In all of those cases it is necessary to handle things
> > in a specific order if there is a dependency.
> 
> My understanding was with deferred probe that it also solves suspend
> ordering problems because things are suspended in reverse order of
> probing.

Devices are suspended in reverse order of _registration_.  Not of 
probing.

Furthermore, that applies only to devices that use synchronous suspend.  
Async suspend is becoming common, and there the only restrictions are 
parent-child relations plus whatever explicit requirements that drivers 
impose by calling device_pm_wait_for_dev().

Alan Stern

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