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authorDoug Anderson <dianders@chromium.org>2013-11-26 16:57:19 -0800
committerWim Van Sebroeck <wim@iguana.be>2014-01-28 21:23:20 +0100
commit178624403c04a4af315583eaf75ebb8545474544 (patch)
tree75481b9bc3cc0bcff0b4bd97e71bffe0fae8dfe1 /drivers/watchdog/s3c2410_wdt.c
parent0f1dd98d896efb956d474754b5d2f0c420d40192 (diff)
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/watchdog/s3c2410_wdt.c')
-rw-r--r--drivers/watchdog/s3c2410_wdt.c13
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 */