The existing watchdog timeout worked OK but didn't deal with
rounding in an ideal way when dividing out all of its clocks.
Specifically if you had a timeout of 32 seconds and an input clock of
66666666, you'd end up setting a timeout of 31.9998 seconds and
reporting a timeout of 31 seconds.
Specifically DBG printouts showed:
s3c2410wdt_set_heartbeat: count=16666656, timeout=32, freq=520833
s3c2410wdt_set_heartbeat: timeout=32, divisor=255, count=16666656 (0000ff4f)
and the final timeout reported to the user was:
((count / divisor) * divisor) / freq
(0xff4f * 255) / 520833 = 31 (truncated from 31.9998)
the technically "correct" value is:
(0xff4f * 255) / (66666666.0 / 128) = 31.9998
By using "DIV_ROUND_UP" we can be a little more correct.
s3c2410wdt_set_heartbeat: count=16666688, timeout=32, freq=520834
s3c2410wdt_set_heartbeat: timeout=32, divisor=255, count=16666688 (0000ff50)
and the final timeout reported to the user:
(0xff50 * 255) / 520834 = 32
the technically "correct" value is:
(0xff50 * 255) / (66666666.0 / 128) = 32.0003
We'll use a DIV_ROUND_UP to solve this, generally erroring on the side
of reporting shorter values to the user and setting the watchdog to
slightly longer than requested:
* Round input frequency up to assume watchdog is counting faster.
* Round divisions by divisor up to give us extra time.
At the same time we can avoid a for loop by just doing the right math.
Signed-off-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
178624403c