linux-kernel - Re: "compatible" and "model" properties in .dts for ARC boards

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Message-ID: <C2D7FE5348E1B147BCA15975FBA23075F44D0C84@IN01WEMBXA.internal.synopsys.com>
Date:	Fri, 6 Nov 2015 04:45:24 +0000
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
CC:	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>,
	"jogo@...nwrt.org" <jogo@...nwrt.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>, Rob Herring <robh@...nel.org>
Subject: Re: "compatible" and "model" properties in .dts for ARC boards

+CC lkml,Arnd, Rob

On Friday 06 November 2015 12:20 AM, Alexey Brodkin wrote:
> Hi Vineet,
>
> During OpenWRT upsreaming process one interesting topic was raised.
> See in the middle of https://lists.openwrt.org/pipermail/openwrt-devel/2015-November/036959.html
>
> In Device Tree descriptions for our boards we don't use "model" property
> even though it is a required one as specified by ePAPR, see
> http://free-electrons.com/~thomas/pub/Power_ePAPR_APPROVED_v1.0.pdf,
> page 39 "Table 3-1 Root node properties".
>
> Instead we put 2 items in "compatible" property.
>
> For example:
> ------------------->8----------------
> compatible = "snps,axs101", "snps,arc-sdp";
> ------------------->8----------------
>
> And from ePAPR standpoint it makes sense to split contents of that "compatible"
> property in 2:
> ------------------->8----------------
> compatible = "snps,arc-sdp";
> model = "snps,axs101";
> ------------------->8----------------

It seems model is just a descriptive label and we can surely add them to existing DT.
compatible on the other hand is more fundamental used for exact comparisons etc
and follows the vendor,device convention.
It is pretty common for compatible to have multiple strings for exactly the same
reason as I have them here. Both axs101 and axs103 are based on sdp thus we want
the ability to have both pieces of information and use as needed.

While doing some other DT research recently, I found some of the best basic DT
documentation is a somewhat misnamed in-kernel document
Documentation/devicetree/booting-without-of.txt


> But I do see problems with implementation of that thing.
> Today we have a luxury of selection of AXS init functionality
> based on that compatible value and if "snps,axs101" goes in
> "model" then we'll need to add some more code in
> arch/arc/plat-axs10x/axs10x.c that reads "model" value with
> of_get_property() and then compare to "axs10{1|3}".
>
> Any thoughts?
>
> -Alexey

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