linux-kernel - Re: [PATCH 1/2] i2c-core: Add gpio based bus arbitration implementation

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Date:	Sat, 15 Dec 2012 23:21:36 +0900
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Naveen Krishna Chatradhi <ch.naveen@...sung.com>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, grundler@...omium.org,
	devicetree-discuss@...ts.ozlabs.org, w.sang@...gutronix.de,
	ben-linux@...ff.org, khali@...ux-fr.org, naveen@...omium.org
Subject: Re: [PATCH 1/2] i2c-core: Add gpio based bus arbitration
 implementation

On Fri, Dec 14, 2012 at 09:06:49AM -0700, Stephen Warren wrote:
> On 12/13/2012 10:50 PM, Naveen Krishna Chatradhi wrote:

> > +The first should be an output, and is used to claim the I2C bus,
> > +the second should be an input, and signals that the other side (Client)
> > +wants to claim the bus. This allows two masters to share the same I2C bus.

> I'm confused why this is even needed; the I2C protocol itself defines
> how multi-master is supposed to work, just using the regular SCL/SDA lines.

Practically speaking essentially no systems actually do that - mostly
Linux will treat failure to get the bus as an error for example.  You
also get things like read operations which appear as multiple
transactions on the I2C bus so require something higher level than what
multi-master provides.

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