From: Mark Brown <broonie-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>
To: Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
Cc: Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>,
Naveen Krishna Chatradhi
<ch.naveen-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
grundler-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org,
devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org,
ben-linux-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org,
khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org,
naveen-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org
Subject: Re: [PATCH 1/2] i2c-core: Add gpio based bus arbitration implementation
Date: Sat, 26 Jan 2013 13:00:06 +0800 [thread overview]
Message-ID: <20130126050004.GC10580@opensource.wolfsonmicro.com> (raw)
In-Reply-To: <20130124113948.GD12933-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
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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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WARNING: multiple messages have this Message-ID (diff)
From: Mark Brown <broonie@opensource.wolfsonmicro.com>
To: Wolfram Sang <w.sang@pengutronix.de>
Cc: Stephen Warren <swarren@wwwdotorg.org>,
Naveen Krishna Chatradhi <ch.naveen@samsung.com>,
linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-samsung-soc@vger.kernel.org, grundler@chromium.org,
devicetree-discuss@lists.ozlabs.org, ben-linux@fluff.org,
khali@linux-fr.org, naveen@chromium.org
Subject: Re: [PATCH 1/2] i2c-core: Add gpio based bus arbitration implementation
Date: Sat, 26 Jan 2013 13:00:06 +0800 [thread overview]
Message-ID: <20130126050004.GC10580@opensource.wolfsonmicro.com> (raw)
In-Reply-To: <20130124113948.GD12933@pengutronix.de>
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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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next prev parent reply other threads:[~2013-01-26 5:00 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-14 5:50 [PATCH 0/2] i2c: Implement generic gpio based bus arbitration Naveen Krishna Chatradhi
[not found] ` <1355464254-12768-1-git-send-email-ch.naveen-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
2012-12-14 5:50 ` [PATCH 1/2] i2c-core: Add gpio based bus arbitration implementation Naveen Krishna Chatradhi
2012-12-14 5:50 ` Naveen Krishna Chatradhi
2012-12-14 16:06 ` Stephen Warren
2012-12-15 14:21 ` Mark Brown
[not found] ` <20121215142135.GB22033-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>
2013-01-24 11:13 ` Wolfram Sang
2013-01-24 11:13 ` Wolfram Sang
[not found] ` <20130124111329.GC12933-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
2013-01-24 11:18 ` Mark Brown
2013-01-24 11:18 ` Mark Brown
[not found] ` <20130124111845.GO4955-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>
2013-01-24 11:39 ` Wolfram Sang
2013-01-24 11:39 ` Wolfram Sang
[not found] ` <20130124113948.GD12933-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
2013-01-26 5:00 ` Mark Brown [this message]
2013-01-26 5:00 ` Mark Brown
[not found] ` <1355464254-12768-2-git-send-email-ch.naveen-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
2012-12-19 12:32 ` Grant Likely
2012-12-19 12:32 ` Grant Likely
2012-12-19 17:14 ` Mark Brown
2012-12-20 0:17 ` Simon Glass
[not found] ` <CAPnjgZ30MQS1OT3GOFLG9HntoD8NrzNw6bB_d1fiJEgHcMDGUA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2012-12-20 0:58 ` Grant Likely
2012-12-20 0:58 ` Grant Likely
[not found] ` <20121219171423.GW4985-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>
2012-12-20 0:53 ` Grant Likely
2012-12-20 0:53 ` Grant Likely
2012-12-14 5:50 ` [PATCH 2/2] i2c-s3c2410: Add GPIO based bus arbitration functionality Naveen Krishna Chatradhi
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