On 11/26/2013 10:30 AM, Doug Anderson wrote:
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.
Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
---
drivers/watchdog/s3c2410_wdt.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
index 7d8fd04..fe2322b 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",
@@ -201,20 +201,20 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
if (count >= 0x10000) {
for (divisor = 1; divisor <= 0x100; divisor++) {
- if ((count / divisor) < 0x10000)
+ if (DIV_ROUND_UP(count, divisor) < 0x10000)
break;
}
Since you are at it,
divisor = DIV_ROUND_UP(count + 1, 0x10000);
might be faster, simpler, and easier to understand than the loop.
Otherwise looks good to me.
Guenter
- 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 */
--
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