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

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Message-ID: <20130124111329.GC12933@pengutronix.de>
Date:	Thu, 24 Jan 2013 12:13:29 +0100
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	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, ben-linux@...ff.org,
	khali@...ux-fr.org, naveen@...omium.org
Subject: Re: [PATCH 1/2] i2c-core: Add gpio based bus arbitration
 implementation

Hi,

On Sat, Dec 15, 2012 at 11:21:36PM +0900, Mark Brown wrote:
> 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.

It is true that Linux currently does not have proper multi-master
support. It is worth a look what is missing and how far we can get with
the I2C specified arbitration IMO.

> 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.

I don't get what you mean here. Can you elaborate?

That being said. Grant's design was the most promising one.

Thanks,

   Wolfram

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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