linux-kernel - Re: [PATCH v1 2/4] ARM: dts: Add i2c-arbitrator bus for exynos5250-snow

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Date:	Wed, 13 Feb 2013 21:42:39 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Doug Anderson <dianders@...omium.org>
CC:	Simon Glass <sjg@...omium.org>,
	Naveen Krishna Chatradhi <ch.naveen@...sung.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Yuvaraj Kumar <yuvaraj.cd@...il.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	u.kleine-koenig@...gutronix.de,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Girish Shivananjappa <girish.shivananjappa@...aro.org>,
	"bhushan.r" <bhushan.r@...sung.com>,
	"sreekumar.c" <sreekumar.c@...sung.com>,
	Prashanth G <prashanth.g@...sung.com>,
	Olof Johansson <olof@...om.net>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Grant Grundler <grundler@...omium.org>,
	Russell King <linux@....linux.org.uk>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Rahul Sharma <rahul.sharma@...sung.com>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wolfram Sang <wolfram@...-dreams.de>
Subject: Re: [PATCH v1 2/4] ARM: dts: Add i2c-arbitrator bus for exynos5250-snow

On 02/13/2013 05:38 PM, Doug Anderson wrote:
> Stephen,
> 
> 
> On Wed, Feb 13, 2013 at 1:04 PM, Stephen Warren <swarren@...dotorg.org> wrote:
>> On 02/13/2013 11:02 AM, Doug Anderson wrote:
>>> We need to use the i2c-arbitrator to talk to any of the devices on i2c
>>> bus 4 on exynos5250-snow so that we don't confuse the embedded
>>> controller (EC).  Add the i2c-arbitrator to the device tree.  As we
>>> add future devices (keyboard, sbs, tps65090) we'll add them on top of
>>> this.
>>>
>>> The arbitrated bus is numbered 104 simply as a convenience to make it
>>> easier for people poking around to guess that it might have something
>>> to do with the physical bus 4.
>>>
>>> The addition is split between the cros5250-common and the snow device
>>> tree file since not all cros5250-class devices use arbitration.

>>> diff --git a/arch/arm/boot/dts/exynos5250-snow.dts b/arch/arm/boot/dts/exynos5250-snow.dts
>>
>>> +     i2c-arbitrator {
>>> +             compatible = "i2c-arbitrator";
>>> +             #address-cells = <1>;
>>> +             #size-cells = <0>;
>>
>>> +             /* Use ID 104 as a hint that we're on physical bus 4 */
>>> +             i2c_104: i2c@0 {
>>
>> Does something use that hint? It sounds a little odd.
> 
> The i2c bus numbering patches will end up creating "/dev/i2c-104".

Oh sorry, I see this is just the alias doing it's job. I'd misread that
as the reg value being 104 and driving the bus ID.
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