linux-kernel - Re: [PATCH 4/5] i2c: omap: query STP always when NACK is received

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Date:	Fri, 7 Jun 2013 22:07:02 +0300
From:	Felipe Balbi <balbi@...com>
To:	Grygorii Strashko <grygorii.strashko@...com>
CC:	Wolfram Sang <wsa@...-dreams.de>, Tony Lindgren <tony@...mide.com>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-i2c@...r.kernel.org>, Kevin Hilman <khilman@...aro.org>,
	Felipe Balbi <balbi@...com>
Subject: Re: [PATCH 4/5] i2c: omap: query STP always when NACK is received

Hi,

On Fri, Jun 07, 2013 at 09:46:07PM +0300, Grygorii Strashko wrote:
> According to I2C specification the NACK should be handled as folowing:
> "When SDA remains HIGH during this ninth clock pulse, this is defined as the Not
> Acknowledge signal. The master can then gene rate either a STOP condition to
> abort the transfer, or a repeated START condition to start a new transfer."

right ...

> [http://www.nxp.com/documents/user_manual/UM10204.pdf]
> 
> The same is recomened by TI I2C wiki:
>  http://processors.wiki.ti.com/index.php/I2C_Tips
> 
> Currently, the OMAP I2C driver interrupts I2C trunsfer in case of NACK, but
> It queries Stop condition OMAP_I2C_CON_REG.STP=1 only if NACK has been received
> during the last message transmitting/recieving.
> This may lead to stuck Bus in "Bus Busy" until I2C IP reset (idle/enable).
> 
> Hence, fix it by querying Stop condition (STP) always when NACK is received.
> 
> CC: Kevin Hilman <khilman@...aro.org>
> CC: Felipe Balbi <balbi@...com>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> ---
>  drivers/i2c/busses/i2c-omap.c |    9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index 46fb8a5..b3daf3f 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -618,11 +618,10 @@ static int omap_i2c_xfer_msg(struct i2c_adapter *adap,
>  	if (dev->cmd_err & OMAP_I2C_STAT_NACK) {
>  		if (msg->flags & I2C_M_IGNORE_NAK)
>  			return 0;
> -		if (stop) {
> -			w = omap_i2c_read_reg(dev, OMAP_I2C_CON_REG);
> -			w |= OMAP_I2C_CON_STP;
> -			omap_i2c_write_reg(dev, OMAP_I2C_CON_REG, w);
> -		}
> +
> +		w = omap_i2c_read_reg(dev, OMAP_I2C_CON_REG);
> +		w |= OMAP_I2C_CON_STP;
> +		omap_i2c_write_reg(dev, OMAP_I2C_CON_REG, w);

... and this is breaking repeated start.

-- 
balbi

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