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

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Date:	Fri, 14 Dec 2012 09:06:49 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Naveen Krishna Chatradhi <ch.naveen@...sung.com>
CC:	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, grundler@...omium.org,
	devicetree-discuss@...ts.ozlabs.org,
	broonie@...nsource.wolfsonmicro.com, 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 12/13/2012 10:50 PM, Naveen Krishna Chatradhi wrote:
> The arbitrator is a general purpose function which uses two GPIOs to
> communicate with another device to claim/release a bus.

> diff --git a/Documentation/devicetree/bindings/i2c/arbitrator-i2c.txt b/Documentation/devicetree/bindings/i2c/arbitrator-i2c.txt
> new file mode 100644
> index 0000000..cb91ea8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/i2c/arbitrator-i2c.txt
> @@ -0,0 +1,56 @@
> +Device-Tree bindings for i2c gpio based bus arbitrator
> +
> +bus-arbitration-gpios :
> +	Two GPIOs to use with the GPIO-based bus arbitration protocol
> +(see below).
> +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.
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