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[PATCH v6 2/5] watchdog: s3c2410_wdt: Fix max_timeout being calculated larger

Sangwook Shin posted 5 patches 1 month, 2 weeks ago
[PATCH v6 2/5] watchdog: s3c2410_wdt: Fix max_timeout being calculated larger
Posted by Sangwook Shin 1 month, 2 weeks ago 
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>
---
 drivers/watchdog/s3c2410_wdt.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
index 95f7207e390a..1e8cf0299713 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 +411,14 @@ 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)
-- 
2.25.1
RE: [PATCH v6 2/5] watchdog: s3c2410_wdt: Fix max_timeout being calculated larger
Posted by Alim Akhtar 2 weeks, 2 days ago 
Hi Sangwook

> -----Original Message-----
> From: Sangwook Shin <sw617.shin@samsung.com>
> Sent: Monday, August 18, 2025 7:48 AM
> To: krzk@kernel.org; alim.akhtar@samsung.com; wim@linux-watchdog.org;
> linux@roeck-us.net; semen.protsenko@linaro.org;
> dongil01.park@samsung.com; khwan.seo@samsung.com
> Cc: linux-arm-kernel@lists.infradead.org; linux-samsung-soc@vger.kernel.org;
> linux-watchdog@vger.kernel.org; linux-kernel@vger.kernel.org; Sangwook Shin
> <sw617.shin@samsung.com>
> Subject: [PATCH v6 2/5] 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: Alim Akhtar <alim.akhtar@samsung.com>
Re: [PATCH v6 2/5] watchdog: s3c2410_wdt: Fix max_timeout being calculated larger
Posted by Guenter Roeck 1 month, 1 week ago 
On Mon, Aug 18, 2025 at 11:18:23AM +0900, Sangwook Shin wrote:
> 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>

> ---
>  drivers/watchdog/s3c2410_wdt.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
> index 95f7207e390a..1e8cf0299713 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 +411,14 @@ 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)
> -- 
> 2.25.1
> 
>
Re: [PATCH v6 2/5] watchdog: s3c2410_wdt: Fix max_timeout being calculated larger
Posted by Sam Protsenko 1 month, 2 weeks ago 
On Sun, Aug 17, 2025 at 9:24 PM Sangwook Shin <sw617.shin@samsung.com> wrote:
>
> 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>
> ---
>  drivers/watchdog/s3c2410_wdt.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
> index 95f7207e390a..1e8cf0299713 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 +411,14 @@ 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;
>  }
>

Thanks for working on this, Sangwook! It looks much better now.

>  static int s3c2410wdt_disable_wdt_reset(struct s3c2410_wdt *wdt, bool mask)
> --
> 2.25.1
>

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