What if I change the 120MHz to 180MHz and then make sure that the I2C operatesShould 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.
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