linux-kernel - Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap

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Date:	Wed, 7 Nov 2012 12:23:25 +0100
From:	Pantelis Antoniou <panto@...oniou-consulting.com>
To:	Benoit Cousson <b-cousson@...com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <robherring2@...il.com>,
	Deepak Saxena <dsaxena@...aro.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Scott Wood <scottwood@...escale.com>,
	Tony Lindgren <tony@...mide.com>, Russ Dill <Russ.Dill@...com>,
	Felipe Balbi <balbi@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Matt Porter <mporter@...com>, <linux-omap@...r.kernel.org>,
	Kevin Hilman <khilman@...com>, Paul Walmsley <paul@...an.com>,
	<devicetree-discuss@...ts.ozlabs.org>
Subject: Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap_devices to mach-omap2)

Hi Benoit,

On Nov 7, 2012, at 12:12 PM, Benoit Cousson wrote:

> On 11/07/2012 12:02 PM, Pantelis Antoniou wrote:
>> Hi Benoit,
>> 

[snip]

>> I don't know if this breaks any conventions but seems to work fine for our case.
> 
> Yeah, my main concern with that approach is that you change the
> structure of the tree by adding an extra node/hierarchy that will not be
> there in case of non-versioned tree.
> That's why I think we should have something lighter that will not change
> the structure.
> Ideally we should be able to add extra versioned node to the original
> dts without changing it at all.
> 

You will still need the versioned nodes to be injected to the non-versioned
ones. FWIW the driver will use the standard of_property_read_* interface.

You can patch of_property_read to hide the version node matching, and it will
work.

I'll leave Grant answer what approach is better, I don't claim to have the insight
to handle all cases.

>>> Maybe some extra version match table can just be passed during the board machine_init 
>>> 
>>> 	of_platform_populate(NULL, omap_dt_match_table, NULL, NULL, panda_version_match_table);
>>> 
>> 
>> Would we need explicit of_platform_populate calls if we have node modification notifiers?
>> In that case the notifier would pick it up automatically, and can do the per
>> version matching internally.
> 
> Yes indeed, but here I was thinking about an intermediate step, i.e.
> now, without any dynamic node insertion mechanism.
> Thanks to this simple approach, when can already fix the board
> versionning problem.
> 

As I pointed, with a kind of injection mechanism. the versioned node contents end up in
the proper place in the device tree.
Your method will work in a much more simpler way.

> Regards,
> Benoit
> 

Regards

-- Pantelis


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