linux-kernel - Re: [2/5] i2c: davinci: query STP always when NACK is received

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Message-ID: <20141121131008.GQ27002@pengutronix.de>
Date:	Fri, 21 Nov 2014 14:10:08 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Grygorii Strashko <grygorii.strashko@...com>
Cc:	Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, Sekhar Nori <nsekhar@...com>,
	Kevin Hilman <khilman@...prootsystems.com>,
	Santosh Shilimkar <ssantosh@...nel.org>,
	Murali Karicheri <m-karicheri2@...com>
Subject: Re: [2/5] i2c: davinci: query STP always when NACK is received

Hello,

On Fri, Nov 21, 2014 at 02:48:57PM +0200, Grygorii Strashko wrote:
> On 11/21/2014 12:19 AM, Uwe Kleine-König wrote:
> >> diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
> >> index 9bbfb8f..2cef115 100644
> >> --- a/drivers/i2c/busses/i2c-davinci.c
> >> +++ b/drivers/i2c/busses/i2c-davinci.c
> >> @@ -411,11 +411,9 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
> >>   	if (dev->cmd_err & DAVINCI_I2C_STR_NACK) {
> >>   		if (msg->flags & I2C_M_IGNORE_NAK)
> >>   			return msg->len;
> >> -		if (stop) {
> >> -			w = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG);
> >> -			w |= DAVINCI_I2C_MDR_STP;
> >> -			davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, w);
> >> -		}
> >> +		w = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG);
> >> +		w |= DAVINCI_I2C_MDR_STP;
> >> +		davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, w);
> > I think this is a good change, but I wonder if the handling of
> > I2C_M_IGNORE_NAK is correct here. If the controller reports a NACK say
> > for the 2nd byte of a 5-byte-message, the transfer supposed to
> > continue, right? (Hmm, maybe the framework handle this and restarts the
> > transfer with I2C_M_NOSTART but the davinci driver doesn't seem to
> > handle this flag?)
> 
> Have nothing to say about handling of I2C_M_IGNORE_NAK. I'm not going to
> change current behavior - davinci driver will interrupt transfer of i2c_msg always
>  in case of NACK and start transfer of the next i2c_msg (if exist).
> In my opinion, Above question is out of scope of this patch.
Yeah right, that's exactly what I thought.

Thinking again I wonder if with your change handling is correct when the
sender wants to do a repeated start. That would need a more detailed
look into the driver.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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