[U-Boot] A question about unconfigured pads check in omap24xx_i2c

[Nikita Kiryanov]

On 11/06/2013 03:19 PM, Lubomir Popov wrote:
> On 06-Nov-13 14:12, Nikita Kiryanov wrote:
>> In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
>> detect unconfigured pads for the i2c bus in use. These checks are
>> all in the form of
>>
>> if (status == I2C_STAT_XRDY) {
>>     printf("unconfigured pads\n");
>>     return -1;
>> }
>>
>> This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
>> that new data is requested for transmission. Why is that indication that
>> the bus is not padconf'd for I2C?
> Hi Nikita,
>
> This has been empirically confirmed on OMAP4 and OMAP5. When the pads
> are not
> configured, the I2C controller is actually disconnected from the bus.
> The clock
> input for its state machine has to come from the bus however due to
> stretching
> etc., although it is internally generated. So actually nothing changes
> within
> the controller after a transaction attempt is made, and it keeps its
> initial
> state with XRDY set only (ready to accept transmit data). I use this as an
> indicator. Not perfect, but works in most cases.
>
> Regards,
> Lubo
>
>

Thanks for the quick reply.
The reason I stumbled across this is that this check hasn't been working
well on our OMAP3 based devices. Some I2C transactions work fine, but
some of them fail this check in the address phase, especially if the I2C
transactions happen in quick successions. We did not have any I2C issues
with the previous driver, and while this behavior is symptomatic of
timing issues playing around with the delays didn't help.
I was wondering if you might have some insights as to what may cause the
controller to behave this way other than unconfigured pads?


-- 
Regards,
Nikita.