linux-kernel - Re: [PATCH] i2c-omap: always send stop after nack

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Message-ID: <51E5137B.7000302@yahoo.es>
Date:	Tue, 16 Jul 2013 17:33:47 +0800
From:	Hein Tibosch <hein_tibosch@...oo.es>
To:	balbi@...com
CC:	Tony Lindgren <tony@...mide.com>,
	linux-i2c <linux-i2c@...r.kernel.org>,
	linux-omap <linux-omap@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c-omap: always send stop after nack

On 7/16/2013 5:03 PM, Felipe Balbi wrote:
> Hi,
>
> On Tue, Jul 16, 2013 at 04:19:35PM +0800, Hein Tibosch wrote:
>> Hi Vikram,
>>
>> On a OMAP4460, i2c-bus-3:
>>
>> A driver (lm75) is causing many 'timeout waiting for bus ready' errors.
>> SDA remains high (as it should), but SCL remains low after a NACK.
>> The bus becomes _unusable for other clients_.
>>
>> While probing, "lm75" writes a command, followed by a read + stop,
>> but the write command is NACK'd. The chip does accept other writes/reads,
>> it just refuses to ack invalid commands.
>>
>> Can you tell me if the patch below would make any sense? Or is it the
>> responsibility of the client to reset the i2c_smbus?
> patch below breaks repeated start.
Hi,

No, after the NACK, no more commands are being processed,
including a repeated start. omap_i2c_xfer() returns -EREMOTEIO
without ever freeing the bus.

The bus is left in an impossible state with SCL constantly low
and all next commands (to different chips) will therefore get
a -ETIMEDOUT

With this patch, the bus will become idle again and new commands
can be processed normally

Hein

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