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

From: Alexander Holler
Date: Tue Aug 26 2014 - 07:01:55 EST

Am 26.08.2014 12:44, schrieb Alexander Holler:
Am 26.08.2014 12:25, schrieb Thierry Reding:
On Tue, Aug 26, 2014 at 11:42:04AM +0200, Alexander Holler wrote:

You need either the type information in the DTB (that's why I've add
"dependencies" to identify phandles), or you need to know every
binding (at
"dependency-resolve-time" to identify phandles. The latter is
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.

That would end up with almost the same ugly driver-based workarounds as
now. It's much better if a driver author only has to define it's
prerequisits (in form of dependencies in the dts) and could be sure the
driver will only be probed if those are met, than to do that stuff based
on a subsystem or even driver level.

If you add dependency-information to drivers, you have two problems:

- How do you get these information from the driver (remember, currently
there is only one initial call, a initcall which might do almost anything)

- These information might become outdated and you would have to change
all drivers. E.g. if the name of a dependency (driver) changes it
wouldn't be done with changing the dts (maybe plural), but you would
have to change the source of all dependant drivers too.

And after having sorted my brain:

A driver depends on a binding (and its API), but not on explicit named other drivers. So trying it (again) on driver level is doomed to fail.

Alexander Holler
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