linux-kernel - Re: i2c-i801 retries on lost arbitration (resent: no gpg)

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Message-ID: <20100430114822.1a5e0cf9@hyperion.delvare>
Date:	Fri, 30 Apr 2010 11:48:22 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	"Ben Dooks (embedded platforms)" <ben-linux@...ff.org>,
	Wolfram Sang <w.sang@...gutronix.de>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: i2c-i801 retries on lost arbitration (resent: no gpg)

Hi Sergey,

On Fri, 30 Apr 2010 12:44:12 +0300, Sergey Senozhatsky wrote:
> Soory, forgot to turn-off gpg.

gpg is fine.

> Both i2c spec and ICH7 datasheet requires to restart transaction in
> case of lost arbitration.
> 
> "No information is lost during the arbitration process. A master that
> loses the arbitration can generate clock pulses until the end of the
> byte in which it loses the arbitration and must restart its transaction
> when the bus is idle."
>         
> Please see the following patch. Is it correct?

No, it's not. As you wrote above, this is not specific to the Intel ICH
but a general I2C issue. As such it must be handled in i2c-core and not
by individual drivers. And as a matter of fact, it is already handled.
Look at functions i2c_transfer and i2c_smbus_xfer in i2c-core.c, see
the comments "Retry automatically on arbitration loss", the code is
already there. It's just a matter of bus drivers properly setting
adapter->retries (which i2c-i801.c does already.)

So I don't know which kernel you're using, but with the latest upstream
kernel, things should work just fine already.

-- 
Jean Delvare
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