On Saturday, August 2, 2025 at 1:12 PM Sam Protsenko <semen.protsenko@xxxxxxxxxx> wrote:
> How about something like this instead?
>
> 8<--------------------------------------------------------------------->8
> static inline unsigned int s3c2410wdt_max_timeout(unsigned long freq) {
> const u64 div_max = (S3C2410_WTCON_PRESCALE_MAX + 1) *
> S3C2410_WTCON_MAXDIV; /* 32768 */
> const u64 n_max = S3C2410_WTCNT_MAXCNT * div_max;
> u64 t_max = n_max / freq;
>
> if (t_max > UINT_MAX)
> t_max = UINT_MAX;
>
> return (unsigned int)t_max;
> }
> 8<--------------------------------------------------------------------->8
>
> This implementation's result:
> - is never greater than real timeout, as it loses the decimal part after
> integer division in t_max
> - much closer to the real timeout value, as it benefits from very big
> n_max in the numerator (this is the main trick here)
> - prepared for using 32-bit max counter value in your next patch, as it
> uses u64 type for calculations
>
> For example, at the clock frequency of 33 kHz:
> - real timeout is: 65074.269 sec
> - old function returns: 65535 sec
> - your function returns: 32767 sec
> - the suggested function returns: 65074 sec
Thank you for your feedback.
I'll make the code changes as follows in the next patch set:
static inline unsigned int s3c2410wdt_max_timeout(struct s3c2410_wdt *wdt)
{
const unsigned long freq = s3c2410wdt_get_freq(wdt);
+ const u64 div_max = (S3C2410_WTCON_PRESCALE_MAX + 1) *
+ S3C2410_WTCON_MAXDIV;
+ const u64 n_max = S3C2410_WTCNT_MAXCNT * div_max;
+ u64 t_max = 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 (unsigned int)t_max;
}
