On 05/15/2018 06:22 AM, Chris Chiu wrote:

What if I change the 120MHz to 180MHz and then make sure that the I2C operates
in target FS mode frequency 400kHz via scope? Would there be any side effect?
Maybe some other busses frequency could be also affected and causing some other
component malfunction?

Should be safe. It is only clock rate information when registering a 
fixed clock with known rate in intel-lpss.c and i2c-designware uses that 
info when calculating the timing parameters. I.e. it doesn't change any 
internal clocks.

I'm trying to find a contact who can confirm what is the expected rate 
of I2C input clock and is it common to all Cannon Lake HW.

-- 
Jarkko