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

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Message-Id: <E1XLu15-0002DP-6o@jdl.com>
Date:	Mon, 25 Aug 2014 08:08:59 -0500
From:	Jon Loeliger <jdl@....com>
To:	Thierry Reding <thierry.reding@...il.com>
cc:	Mark Rutland <mark.rutland@....com>,
	Alexander Holler <holler@...oftware.de>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"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)

> 

> Anyway, instead of going back and forth between "deferred probe is good"
> and "deferred probe is bad", how about we do something useful now and
> concentrate on how to make use of the information we have in DT with the
> goal to reduce the number of cases where deferred probing is required?

Good idea.

The proposal on the table is to allow the probe code
to make a topological sort of the devices based on
dependency information either implied, explicitly stated
or both.  That is likely a fundamentally correct approach.

I believe some of the issues that need to be resolved are:

    1) What constitutes a dependency?
    2) How is that dependency expressed?
    3) How do we add missing dependencies?
    4) Backward compatability problems.

There are other questions, of course.  Is it a topsort
per bus?  Are there required "early devices"?  Should
the inter-node dependencies be expressed at each node,
or in a separate hierarchy within the DTS?  Others.

HTH,
jdl
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