linux-kernel - Re: [dtc RFC PATCH] Enforce node name unit-address presence/absence

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Date:	Thu, 19 Sep 2013 22:31:03 +1000
From:	David Gibson <david@...son.dropbear.id.au>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Olof Johansson <olof@...om.net>, Jon Loeliger <jdl@....com>,
	Frank Rowand <frowand.list@...il.com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Stephen Warren <swarren@...dia.com>
Subject: Re: [dtc RFC PATCH] Enforce node name unit-address presence/absence

On Wed, Sep 18, 2013 at 05:02:20PM -0600, Stephen Warren wrote:
> On 09/18/2013 02:41 PM, Olof Johansson wrote:
> > On Wed, Sep 18, 2013 at 1:23 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> >> From: Stephen Warren <swarren@...dia.com>
> >>
> >> ePAPR 1.1 section 2.2.1.1 "Node Name Requirements" specifies that any
> >> node that has a reg property must include a unit address in its name
> >> with value matching the first entry in its reg property. Conversely, if
> >> a node does not have a reg property, the node name must not include a
> >> unit address.
> >>
> >> Implement a check for this. The code doesn't validate the format of the
> >> unit address; ePAPR implies this may vary from binding to binding, so
> >> I'm not sure that it's possible to validate the value itself.
> ...
> > Anyway, I think it'd be better to produce warnings than errors for
> > this. That way we could also merge it now while the trees are fixed
> > up.
> 
> Yes, that makes sense.
> 
> > Also, maybe warn for @0x<foo>, which is another unpreferred syntax, it
> > should just be @<foo> (with foo being in hex).
> 
> ePAPR doesn't seem to disallow that; it explicitly says that the
> unit-address consists of the characters from table 2-1, which is the
> same table of characters used for the node name itself. However, it does
> state that the binding for a particular bus may impose additional
> restrictions; should I implement such a check but limit it to the root
> node or specific known bus types? That would require explicitly
> whitelisting the check for a lot of bus types, given that each I2C/...
> controller binding is a bus type...

Yeah, I think that's the wrong approach.  Instead I think we need a
table of bus type -> unit address validation functions.  That way we
can start with the common ones - plain memory address, PCI, USB and
I2C, then add more as we need them.

I actually started implementing this once, but I seem to have lost the
patch.

One thing to bear in mind if you do have a crack at this - the correct
encoding of reg -> unit address isn't always unique, although it
usually is.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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