linux-kernel - Re: "memory" binding issues

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Date:	Mon, 16 Sep 2013 15:48:22 -0700
From:	Olof Johansson <olof@...om.net>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	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>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: "memory" binding issues

On Mon, Sep 16, 2013 at 3:46 PM, Benjamin Herrenschmidt
<benh@...nel.crashing.org> wrote:
> On Mon, 2013-09-16 at 10:17 -0600, Stephen Warren wrote:
>> On 09/15/2013 08:57 PM, Benjamin Herrenschmidt wrote:
>> > [resent to the right list this time around]
>> >
>> > Hi folks !
>> >
>> > So I don't have the bandwidth to follow closely what's going on, but I
>> > just today noticed the crackpot that went into 3.11 as part of commit:
>> >
>> > 9d8eab7af79cb4ce2de5de39f82c455b1f796963
>> > drivers: of: add initialization code for dma reserved memory
>> >
>> > Fist of all, do NOT add (or change) a binding as part of a patch
>> > implementing code, it's gross.
>>
>> Personally, I would argue the opposite; it's much easier to see what's
>> going on when it's all together in one patch.
>
> One patch series eventually, but not the same patch.
>
>> Ensuring ABI stability can
>> only be achieved through code review, i.e. splitting into separate
>> DT/code patches won't achieve that, so that argument doesn't affect this.
>>
>> ...
>> > Additionally, it has the following issues:
>> >
>> >  - It describes the "memory" node as /memory, which is WRONG
>> >
>> > 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.


-Olof
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