On Saturday, August 2, 2025 at 1:12 PM Sam Protsenko [off-list ref] 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;
 }