lkml.org 
[lkml]   [2014]   [Nov]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [2/5] i2c: davinci: query STP always when NACK is received
Hi Uwe,

On 11/21/2014 03:10 PM, Uwe Kleine-König wrote:
> 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.

Davinci driver will always abort transfer with error -EREMOTEIO in case if
NACK received from I2C slave device. And the next omap_i2c_xfer() call may
be *not* targeted to the same I2C slave device.
^ if !I2C_M_IGNORE_NAK

This discussion is absolutely similar to https://lkml.org/lkml/2013/7/16/235
So, I'm just copy-pasting my answers from there ;)

regards,
-grygorii
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2014-11-21 17:01    [W:0.114 / U:2.952 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site