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

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Message-ID: <20130126050004.GC10580@opensource.wolfsonmicro.com>
Date:	Sat, 26 Jan 2013 13:00:06 +0800
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Wolfram Sang <w.sang@...gutronix.de>
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

On Thu, Jan 24, 2013 at 12:39:48PM +0100, Wolfram Sang wrote:
> On Thu, Jan 24, 2013 at 07:18:47PM +0800, Mark Brown wrote:

> > A read is typically implemented as a write of the register address
> > followed by a read of the value, usually with the ability to free the
> > bus in between.  If two devices attempt to access the register map
> > simultaneously this results in the address going wrong.

> Could happen. But in what situations will one not use repeated start
> here? Especially when designing a multi-master bus?

Well, you're depending on the specific drivers doing things that way and
it's actually quite rare for the controller drivers in Linux to support
I2C_M_NOSTART which discourages this.

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