[PATCH v5 2/5] watchdog: s3c2410_wdt: Fix max_timeout being calculated larger

[Sangwook Shin]

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.

Signed-off-by: Sangwook Shin <sw617.shin at samsung.com>
---
 drivers/watchdog/s3c2410_wdt.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
index 95f7207e390a..0a4c0ab2a3d6 100644
--- 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 +411,13 @@ 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);
+	//(S3C2410_WTCON_PRESCALE_MAX + 1) * S3C2410_WTCON_MAXDIV = 0x8000
+	u64 t_max = div64_ul((u64)S3C2410_WTCNT_MAXCNT * 0x8000, 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)
-- 
2.25.1