linux-kernel - Re: "memory" binding issues

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Message-Id: <20130918013112.1104CC42BDB@trevor.secretlab.ca>
Date:	Tue, 17 Sep 2013 18:31:12 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Tomasz Figa <tomasz.figa@...il.com>,
	Olof Johansson <olof@...om.net>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Stephen Warren <swarren@...dotorg.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Stephen Warren <swarren@...dia.com>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: "memory" binding issues

On Tue, 17 Sep 2013 09:56:39 +0200, Tomasz Figa <tomasz.figa@...il.com> wrote:
> On Monday 16 of September 2013 15:48:22 Olof Johansson wrote:
> > On Mon, Sep 16, 2013 at 3:46 PM, Benjamin Herrenschmidt
> > > On Mon, 2013-09-16 at 10:17 -0600, Stephen Warren wrote:
> > >> On 09/15/2013 08:57 PM, Benjamin Herrenschmidt wrote:
> > >> > It should be "/memory@...t-address, this is important because the
> > >> > Linux
> > >> > kernel of_find_device_by_path() isn't smart enough to do partial
> > >> > searches (unlike the real OFW one) and thus to ignore the unit
> > >> > address
> > >> > for search purposes, and you *need* the unit address if you have
> > >> > multiple memory nodes (which you typically do on NUMA machines).
> > >> 
> > >> Perhaps /memory should have had a unit-address, but it never has had
> > >> on
> > > 
> > >> ARM; see arch/arm/boot/dts/skeleton.dtsi which says:
> > > Well, this is a mistake ARM folks might have done from day one but it
> > > should still be fixed :-)
> > > 
> > > A node that has a "reg" property should have the corresponding unit
> > > address.
> > 
> > No, absolutely _NOT_ a requirement. Unit address is only required if
> > needed to disambiguate two properties with the same name.
> > 
> > If there are no ambiguities, then leaving off the unit address is much
> > preferred.
> 
> I'm afraid that I must disagree. For consistency I'd rather go with what 
> Ben said. Please see ePAPR chapter 2.2.1.1, which clearly defines how 
> nodes should be named.

Regardless of the ePAPR spec, there is loads of precidence of having a
single memory node without the unit address, and we have to continue to
support those device trees. Just do a "git grep 'memory ' arch/*/boot/dts/*"
to get a big list. You'll note that there are a lot of powerpc matches
in that list.

Similarly, if the kernel chokes on memory node(s) that have the unit
address then that is a bug and needs to be fixed.

g.
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