linux-kernel - Re: [PATCH] AB3100 regulator support v1

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Date:	Sun, 30 Aug 2009 20:01:07 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linus Walleij <linus.ml.walleij@...il.com>,
	linux-kernel@...r.kernel.org,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: [PATCH] AB3100 regulator support v1

On Sun, Aug 30, 2009 at 12:27:32PM -0400, Alan Stern wrote:
> On Sun, 30 Aug 2009, Mark Brown wrote:

> > On the face of it (and without having actually looked at a running
> > system or anything yet) I'm rather surprised that platform based MFD
> > drivers aren't running into this issue more often.  CCing in Alan who
> > made the change.

> I'm not at all familiar with the detailed issues involved here.  
> Perhaps because of this, I don't see why there's any reason for
> deadlocking.  __driver_attach() is invoked when a new driver is
> registered; to avoid problems all you have to do is make sure you
> aren't holding any device locks when you register a driver.

Ah, it's platform_driver_probe() that's causing issues.  When it is used
the devices need to have been registered previously since the driver
probe function isn't kept around.  In order to do this for the child
device the driver for the subdevice has to be registered from within the
probe function of the parent, which is itself happening within the
parent device registration.
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