linux-kernel - Re: [PATCH 1/2] i2c: mux: add device tree support

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Date:	Mon, 23 Apr 2012 10:13:19 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Wolfram Sang <w.sang@...gutronix.de>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Ben Dooks <ben-linux@...ff.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	devicetree-discuss@...ts.ozlabs.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, Stephen Warren <swarren@...dia.com>,
	David Daney <ddaney.cavm@...il.com>
Subject: Re: [PATCH 1/2] i2c: mux: add device tree support

On 04/23/2012 05:15 AM, Wolfram Sang wrote:
> On Tue, Apr 17, 2012 at 12:49:04PM -0600, Stephen Warren wrote:
>> From: Stephen Warren <swarren@...dia.com>
>>
>> * Define core portions of the DT binding for I2C bus muxes.
>> * Enhance i2c_add_mux_adapter():
>> ** Add parameters required for DT support. Update all callers.
>> ** Set the appropriate adap->dev.of_node for the child bus.
>> ** Call of_i2c_register_devices() for the child bus.
>>
>> Signed-off-by: Stephen Warren <swarren@...dia.com>
> 
> David Daney (CCed) posted another variant [1]. Just looking at the
> patches (and not really using them), I tend to like the approach using
> <reg> better. But I am open for discussion, so I'd appreciate your
> feedback.
> 
> Regards,
> 
>    Wolfram
> 
> [1] http://lkml.org/lkml/2012/4/12/423

Ah, that does look like a reasonable binding.

I had meant to call out to reviewers the potentially unusual use of
explicitly named sub-nodes, rather than using the usual reg-based matching.

The main reason I chose named sub-nodes for the busses was so the
sub-nodes would match the pinctrl named states. However, I think we can
make the pinctrl numbering match rather than the pinctrl naming instead.
The only issue is the "idle" state; if we allow it to exist anywhere in
the pinctrl-names list, it'll make the pinctrl numbering mismatch the
sub-node numbering. I think we can solve this by forcing the idle state
to be listed last in pinctrl-names (if it's listed at all). I'll update
my patches based on that David's patch.
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