linux-kernel - Re: [PATCH 3/6] mfd: 88pm860x: enhance lock on i2c transaction

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Message-ID: <20110513182731.GX8970@sortiz-mobl>
Date:	Fri, 13 May 2011 20:27:32 +0200
From:	Samuel Ortiz <sameo@...ux.intel.com>
To:	Haojian Zhuang <haojian.zhuang@...il.com>
Cc:	Haojian Zhuang <haojian.zhuang@...vell.com>,
	linux-kernel@...r.kernel.org, lrg@...mlogic.co.uk,
	broonie@...nsource.wolfsonmicro.com, a.zummo@...ertech.it,
	khali@...ux-fr.org, ben-linux@...ff.org
Subject: Re: [PATCH 3/6] mfd: 88pm860x: enhance lock on i2c transaction

Hi Haojian,

On Fri, May 13, 2011 at 11:00:24PM +0800, Haojian Zhuang wrote:
> On Fri, May 13, 2011 at 10:20 PM, Samuel Ortiz <sameo@...ux.intel.com> wrote:
> > Hi Haojian,
> >
> > On Fri, May 06, 2011 at 05:21:22PM +0800, Haojian Zhuang wrote:
> >> Accessing test page in 88pm860x is a sequence of read/write on i2c bus.
> >> Bus lock is used in each small i2c transaction. But it may result the
> >> whole sequence interrupted by other i2c client transaction.
> > Sure, but what you mainly want is your MFD i2c IO calls to be serialized, and
> > that's already being taken care of by the current code.
> > Are other i2c clients (non MFD ones) touching the same i2c registers than the
> > MFD ones ?
> >
> Other process may not access the same register. But they may access same i2c
> bus. What I did is used to protect bus operation.
> 
> Even accessing one register in test page is composed by a sequence of accessing
> test page.
> 
> For example, read one byte of 0xbc in test page.
> 1) i2c read zero byte from 0xFA
> 2) i2c read zero byte from 0xFB
> 3) i2c read zero byte from 0xFF
> 4) i2c read one byte from 0xbc (desired operation)
> 5) i2c read zero byte from 0xFC
> 
> Step #1 to #3 is used to enter test page mode. Step 4 is used to read
> desired data.
> Step #5 is used to exit test page mode. If all these five steps are
> using standard
> i2c read operation, bus lock in i2c driver will be held and released
> five times. If another
> process is also accessing i2c bus, it may interrupt the sequence and
> import error to
> pmic.
I see. Wouldn't i2c_transfer() fix your problem then ?

Cheers,
Samuel.

-- 
Intel Open Source Technology Centre
http://oss.intel.com/
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