linux-kernel - Re: [PATCH 3/4] i2c: omap: don't reset controller if Arbitration Lost detected

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Message-ID: <20141121181125.GD3754@katana>
Date:	Fri, 21 Nov 2014 19:11:25 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Alexander Kochetkov <al.kochet@...il.com>
Cc:	linux-omap@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
	Felipe Balbi <balbi@...com>
Subject: Re: [PATCH 3/4] i2c: omap: don't reset controller if Arbitration
 Lost detected

On Fri, Nov 21, 2014 at 01:28:44AM +0400, Alexander Kochetkov wrote:
> Arbitration Lost is a expected situation in a multimaster environment.
> IP correctly detect it.
> 
> The only reason for reseting IP in the AL case is to be sure to
> avoid advisory 1.94 (omap3) and errata i595 (omap4):
> "I2C: After an Arbitration is Lost the Module Incorrectly Starts
> the Next Transfer" with workaround: "The MST and STT bits inside
> I2C_CON should be set to 1 at the same moment (avoid setting the
> MST bit to 1 while STT = 0)."
> 
> The driver never writes MST and STT bits separately and doesn't
> create condition for errata. So the reset is not necessary.
> 
> Tested on Beagleboard XM C.
> 
> Signed-off-by: Alexander Kochetkov <al.kochet@...il.com>
> ---
>  drivers/i2c/busses/i2c-omap.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index 3ffb9c0..47103e7 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -707,13 +707,17 @@ static int omap_i2c_xfer_msg(struct i2c_adapter *adap,
>  		return 0;
>  
>  	/* We have an error */
> -	if (dev->cmd_err & (OMAP_I2C_STAT_AL | OMAP_I2C_STAT_ROVR |
> +	if (dev->cmd_err & (OMAP_I2C_STAT_ROVR |
>  			    OMAP_I2C_STAT_XUDF)) {
>  		omap_i2c_reset(dev);
>  		__omap_i2c_init(dev);
>  		return -EIO;
>  	}
>  
> +	if (dev->cmd_err & OMAP_I2C_STAT_AL) {
> +		return -EIO;
> +	}

The errno for AL is -EAGAIN. Curly braces are not needed.

> +
>  	if (dev->cmd_err & OMAP_I2C_STAT_NACK) {
>  		if (msg->flags & I2C_M_IGNORE_NAK)
>  			return 0;
> -- 
> 1.7.9.5
> 

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