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

From: Thierry Reding
Date: Tue Aug 26 2014 - 06:25:16 EST

On Tue, Aug 26, 2014 at 11:42:04AM +0200, Alexander Holler wrote:
> Am 26.08.2014 10:49, schrieb Thierry Reding:
> >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@xxxxxxxxx> 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.
> You need either the type information in the DTB (that's why I've add those
> "dependencies" to identify phandles), or you need to know every binding (at
> "dependency-resolve-time" to identify phandles. The latter is impracticable
> to implement in a generic way (for use with every possible binding).

Like I already mentioned, this could be done in drivers who contain that
information already anyway. Or parts of it could be done in subsystem-
specific callbacks where a generic binding is available.


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