linux-kernel - Re: [PATCH v4 04/22] of: add function to allow probing a device from a OF node

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Date:	Wed, 16 Sep 2015 20:35:19 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Thierry Reding <thierry.reding@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-acpi@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH v4 04/22] of: add function to allow probing a device from
 a OF node

On Wed, Sep 16, 2015 at 10:17:43AM +0200, Tomeu Vizoso wrote:

> AFAICS, this is a must currently for correct operation in simple-bus
> and simple-mfd situations, because probing order is currently very
> unpredictable and it's totally possible for the probing of a child to
> start before the probing of its parent has finished (if async probing
> is enabled or if a module is loaded that registers a child's driver at
> the wrong time).

Hrm.  That's worrying for devices that rely on peering into their parent
device for things...

> I would prefer if the core would take care of making sure that parents
> are always probed before their children, but the unconditional locking
> of the parent device stands in the way.

In the MFD case this is another reason for not putting the device
structure into the DT - if it isn't then the ordering is controlled by
the device being instantiated.

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