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| author | Doug Anderson <dianders@chromium.org> | 2013-11-26 16:57:19 -0800 |
|---|---|---|
| committer | Wim Van Sebroeck <wim@iguana.be> | 2014-01-28 21:23:20 +0100 |
| commit | 178624403c04a4af315583eaf75ebb8545474544 (patch) | |
| tree | 75481b9bc3cc0bcff0b4bd97e71bffe0fae8dfe1 /drivers | |
| parent | 0f1dd98d896efb956d474754b5d2f0c420d40192 (diff) | |
| download | linux-178624403c04a4af315583eaf75ebb8545474544.tar.bz2 | |
watchdog: s3c2410_wdt: Handle rounding a little better for timeout
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>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/watchdog/s3c2410_wdt.c | 13 |
1 files changed, 5 insertions, 8 deletions
diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c index c1ada330e125..8beaa1799df6 100644 --- a/drivers/watchdog/s3c2410_wdt.c +++ b/drivers/watchdog/s3c2410_wdt.c @@ -188,7 +188,7 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou if (timeout < 1) return -EINVAL; - freq /= 128; + freq = DIV_ROUND_UP(freq, 128); count = timeout * freq; DBG("%s: count=%d, timeout=%d, freq=%lu\n", @@ -200,21 +200,18 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou */ if (count >= 0x10000) { - for (divisor = 1; divisor <= 0x100; divisor++) { - if ((count / divisor) < 0x10000) - break; - } + divisor = DIV_ROUND_UP(count, 0xffff); - if ((count / divisor) >= 0x10000) { + if (divisor > 0x100) { dev_err(wdt->dev, "timeout %d too big\n", timeout); return -EINVAL; } } DBG("%s: timeout=%d, divisor=%d, count=%d (%08x)\n", - __func__, timeout, divisor, count, count/divisor); + __func__, timeout, divisor, count, DIV_ROUND_UP(count, divisor)); - count /= divisor; + count = DIV_ROUND_UP(count, divisor); wdt->count = count; /* update the pre-scaler */ |