linux-kernel - Re: "memory" binding issues

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Message-ID: <52372F2A.2050003@wwwdotorg.org>
Date:	Mon, 16 Sep 2013 10:17:46 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	devicetree@...r.kernel.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	m.szyprowski@...sung.com, swarren@...dia.com,
	rob.herring@...xeda.com, Grant Likely <grant.likely@...retlab.ca>
Subject: Re: "memory" binding issues

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. 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:

        memory { device_type = "memory"; reg = <0 0>; };

... and the fact that reg in /memory can have multiple entries seems to
support the expectation we only have a single node here. I'm not sure
how we could possibly change this now it's become so entrenched?
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