Re: 2.6.29 unexplained delay seen in i2c-imx.c driver

On 12/11/13 04:01 PM, Steven King wrote:
> On Tuesday 12 November 2013 11:15:07 am Priscilla Wong wrote:
>    
>> Can someone help me on an issue I am seeing on my i2c-imx driver for
>> uClinux 2.6.29?
>>
>> Attached is a scope capture of an i2c read operation.  In the capture,
>> yellow is clock, green is data, blue and pink are both gpios I am using
>> for debugging.  It can be seen that there is a 300 us delay after master
>> writes to the slave address. The transfer is complete when the interrupt
>> arrives and waitqueue is woken up. The pink gpio fires high during the
>> transfer complete call (i2c_imx_trx_complete) after the slave address is
>> written. The blue gpio fires high during the queue wake up call in the
>> ISR (i2c_imx_isr). When looking at this capture, my first inclination is
>> to bump the interrupt level and priority, hoping it will speed up the
>> ISR but it had no effect on the delay.
>>
>> Any ideas what is causing this delay?
>>      
> That looks similar to an issue with the original version of my i2c-coldfire
> driver; the scheduler simply can't reschedule tasks any faster than that.
> The fix was to have the isr process the next byte in the transfer and only
> send the completion when the entire message was transfered.
>    
Thanks for your input!

Would changing the implementation to polling based be the answer given 
that i2c-mcf did not have this issue? I've attached a scope image of a 
read access with i2c-mcf (i2c-mcf-i2cget.png). However if switching 
i2c-imx to polling based, the data transferring bit (ICF) also suffers 
from this delay too. It is not set till 228us after the 9th clock cycle 
(See attached scope15.png image, cursor X1 is the 9th clock cycle and X2 
is when ICF is set). Any ideas?

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