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

From: Jon Loeliger <jdl@jdl.com>
To: Thierry Reding <thierry.reding@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Alexander Holler <holler@ahsoftware.de>,
	"grant.likely@linaro.org" <grant.likely@linaro.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Russell King <linux@arm.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rob Herring <robh+dt@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH 0/9] dt: dependencies (for deterministic driver initialization order based on the DT)
Date: Mon, 25 Aug 2014 08:08:59 -0500	[thread overview]
Message-ID: <E1XLu15-0002DP-6o@jdl.com> (raw)
In-Reply-To: <20140825093931.GB2399@ulmo>

> 

> 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