Re: [RFC PATCH 0/9] dt: dependencies (for deterministic driver initialization order based on the DT)
From: Alexander Holler
Date: Tue Aug 26 2014 - 05:42:49 EST
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).
Regards,
Alexander Holler
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