The -1 +1 thingy should probably do what DIV_ROUND_UP does. The 4 is 2
the  "platform_clock => sysclock" and 2 from the computation part. The 64
is the same 4 times 16.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>