Hi Doug, > 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@xxxxxxxxxxxx> > --- > Changes in v2: > - Avoid a for loop as per Guenter. Patch added to linux-watchdog-next. Kind regards, Wim. -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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