watchdog: s3c2410_wdt: Fix max_timeout being calculated larger

Fix the issue of max_timeout being calculated larger than actual value.
The calculation result of freq / (S3C2410_WTCON_PRESCALE_MAX + 1) /
S3C2410_WTCON_MAXDIV is smaller than the actual value because the remainder
is discarded during the calculation process. This leads to a larger
calculated value for max_timeout compared to the actual settable value.
To resolve this issue, the order of calculations in the computation process
has been adjusted.

Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Sangwook Shin <sw617.shin@samsung.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
index 95f7207e390a3633f79eac981ee8646347b1e44f..1e8cf029971311b683a3e4a5e082147865a9b5f1 100644 (file)
--- a/drivers/watchdog/s3c2410_wdt.c
+++ b/drivers/watchdog/s3c2410_wdt.c
@@ -27,6 +27,7 @@
 #include <linux/mfd/syscon.h>
 #include <linux/regmap.h>
 #include <linux/delay.h>
+#include <linux/math64.h>
 
 #define S3C2410_WTCON          0x00
 #define S3C2410_WTDAT          0x04
@@ -410,9 +411,14 @@ static inline unsigned long s3c2410wdt_get_freq(struct s3c2410_wdt *wdt)
 static inline unsigned int s3c2410wdt_max_timeout(struct s3c2410_wdt *wdt)
 {
        const unsigned long freq = s3c2410wdt_get_freq(wdt);
+       const u64 n_max = (u64)(S3C2410_WTCON_PRESCALE_MAX + 1) *
+                       S3C2410_WTCON_MAXDIV * S3C2410_WTCNT_MAXCNT;
+       u64 t_max = div64_ul(n_max, freq);
 
-       return S3C2410_WTCNT_MAXCNT / (freq / (S3C2410_WTCON_PRESCALE_MAX + 1)
-                                      / S3C2410_WTCON_MAXDIV);
+       if (t_max > UINT_MAX)
+               t_max = UINT_MAX;
+
+       return t_max;
 }
 
 static int s3c2410wdt_disable_wdt_reset(struct s3c2410_wdt *wdt, bool mask)