linux-kernel - Re: [RFC PATCH 0/9] dt: dependencies (for deterministic driver initialization order based on the DT)

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Date:	Tue, 26 Aug 2014 10:49:24 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Grant Likely <grant.likely@...aro.org>
Cc:	Jon Loeliger <jdl@....com>, Mark Rutland <mark.rutland@....com>,
	Alexander Holler <holler@...oftware.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <robh+dt@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 0/9] dt: dependencies (for deterministic driver
 initialization order based on the DT)

On Tue, Aug 26, 2014 at 09:42:08AM +0100, Grant Likely wrote:
> On Mon, 25 Aug 2014 15:37:16 +0200, Thierry Reding <thierry.reding@...il.com> wrote:
[...]
> > There are somewhat standardized bindings for the above and especially
> > for bindings of the type that clocks implement this is trivial. We can
> > simply iterate over each (phandle, specifier) tuple and check that the
> > corresponding clock provider can be resolved (which typically means that
> > it's been registered with the common clock framework).
> > 
> > For regulators (and regulator-like bindings) the problem is somewhat
> > more difficult because they property names are not standardized. One way
> > to solve this would be to look for property names with a -supply suffix,
> > but that could obviously lead to false positives. One alternative that I
> > think could eliminate this would be to explicitly list dependencies in
> > drivers. This would allow core code to step through such a list and
> > resolve the (phandle, specifier) tuples.
> 
> False positives and negatives may not actually be a problem. It is
> suboptimal, certainly, but it shouldn't outright break the kernel.

There could be cases where some random integer in a cell could be
interpreted as a phandle and resolve to a struct device_node. I suppose
it might be unlikely, but not impossible, that the device_node could
even match a device in the correct subsystem and you'd get a wrong
dependency. Granted, a wrong dependency may not be catastrophic in that
it won't lead to a crash, but it could lead to various kinds of
weirdness and hard to diagnose problems.

Thierry

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