linux-kernel - Re: [PATCH v2 3/4] i2c: omap: don't reset controller if Arbitration Lost detected

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Message-ID: <20141122010728.GB26751@saruman>
Date:	Fri, 21 Nov 2014 19:07:28 -0600
From:	Felipe Balbi <balbi@...com>
To:	Alexander Kochetkov <al.kochet@...il.com>
CC:	<linux-omap@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Wolfram Sang <wsa@...-dreams.de>,
	Tony Lindgren <tony@...mide.com>, Felipe Balbi <balbi@...com>
Subject: Re: [PATCH v2 3/4] i2c: omap: don't reset controller if Arbitration
 Lost detected

On Sat, Nov 22, 2014 at 02:51:47AM +0400, Alexander Kochetkov wrote:
> Arbitration Lost is an expected situation in a multimaster
> environment. I2C controller (IP) correctly detect and report AL.
> 
> The only one visible reason for reseting IP in the AL case is
> to avoid advisory 1.94 (omap3) and errata i595 (omap4): "I2C:
> After an Arbitration is Lost the Module Incorrectly Starts
> the Next Transfer".
> 
> Errata workaround states: "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 set MST and STT bits
> separately and doesn't create condition for errata. So the reset
> is not necessary.
> 
> Also corrected return value for AL to -EAGAIN.
> 
> Tested on Beagleboard XM C.
> 
> Signed-off-by: Alexander Kochetkov <al.kochet@...il.com>

you could have kept my tested-by and reviewed-by:

Tested-by: Felipe Balbi <balbi@...com>
Reviewed-by: Felipe Balbi <balbi@...com>


> On 21.10.2014 21:11, Wolfram Sang <wsa@...-dreams.de> wrote:
> > The errno for AL is -EAGAIN. Curly braces are not needed.
> 
> Thank you, Wolfram, fixed.
> 
>  drivers/i2c/busses/i2c-omap.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index 3ffb9c0..02da567 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -707,13 +707,15 @@ 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 |
> -			    OMAP_I2C_STAT_XUDF)) {
> +	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 -EAGAIN;
> +
>  	if (dev->cmd_err & OMAP_I2C_STAT_NACK) {
>  		if (msg->flags & I2C_M_IGNORE_NAK)
>  			return 0;
> -- 
> 1.7.9.5
> 

-- 
balbi

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