Re: [PATCH] Let PCA9564 recover from unacked data byte (state 0x30)

[Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

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Hi Enrik,

On Tue, Apr 07, 2009 at 12:38:56PM +0200, Enrik Berkhan wrote:
> Currently, the i2c-algo-pca driver does nothing if the chip enters state
> 0x30 (Data byte in I2CDAT has been transmitted; NOT ACK has been
> received).  Thus, the i2c bus connected to the controller gets stuck
> afterwards.
> 
> I have seen this kind of error on a custom board in certain load
> situations most probably caused by interference or noise.
> 
> A possible reaction is to let the controller generate a STOP condition.
> This is documented in the controller data sheet and the same is done for
> other NACK states as well.
> 
> Signed-off-by: Enrik Berkhan <Enrik.Berkhan-JJi787mZWgc@public.gmane.org>
> ---
>  drivers/i2c/algos/i2c-algo-pca.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> Index: drivers/i2c/algos/i2c-algo-pca.c
> ===================================================================
> --- drivers/i2c/algos/i2c-algo-pca.c.orig	2009-04-07 11:23:08.000000000 +0200
> +++ drivers/i2c/algos/i2c-algo-pca.c	2009-04-07 11:24:56.000000000 +0200
> @@ -270,10 +270,12 @@ static int pca_xfer(struct i2c_adapter *
>  
>  		case 0x30: /* Data byte in I2CDAT has been transmitted; NOT ACK has been received */
>  			DEB2("NOT ACK received after data byte\n");
> +			pca_stop(adap);

This looks okay.

>  			goto out;
>  
>  		case 0x38: /* Arbitration lost during SLA+W, SLA+R or data bytes */
>  			DEB2("Arbitration lost\n");
> +			// XXX pca_start()? pca_reset()?

(No // comments, see CodingStyle)

I think we should do something here, too. The manual says something about doing
another start. What about doing this and adding a comment that possibly a reset
is another thing to try in case of problems?

>  			goto out;
>  
>  		case 0x58: /* Data byte has been received; NOT ACK has been returned */

-- 
Pengutronix e.K.                           | Wolfram Sang                |
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