linux-kernel - RE: [PATCH v4 2/4] watchdog: s3c2410_wdt: Fix max

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Message-ID: <008501dc05da$36362600$a2a27200$@samsung.com>
Date: Tue, 5 Aug 2025 16:26:08 +0900
From: <sw617.shin@...sung.com>
To: "'Sam Protsenko'" <semen.protsenko@...aro.org>, "'Guenter Roeck'"
	<linux@...ck-us.net>
Cc: <krzk@...nel.org>, <alim.akhtar@...sung.com>, <wim@...ux-watchdog.org>,
	<khwan.seo@...sung.com>, <dongil01.park@...sung.com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-samsung-soc@...r.kernel.org>,
	<linux-watchdog@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 2/4] watchdog: s3c2410_wdt: Fix max_timeout being
 calculated larger

On Tuesday, August 5, 2025 at 2:03 PM Sam Protsenko <semen.protsenko@...aro.org> wrote:

> 
> > > +       u64 t_max = n_max / freq;
> > >
> >
> > Make sure this compiles on 32-bit builds.
> >
> 
> Can you please elaborate what might be the possible problem -- just
> curious? I admit I never though about 32-bit case when writing that code,
> but don't see any immediate issues with that too.
> 

In my opinion, it seems that Gunter Reck's explanation is correct.
I've found out that the error of "undefined reference to '__aeabi_uldivmod'" may occur when compiling new code on a 32-bit architecture.
If you don't mind, I would like to proceed with maintaining the previous revision below.
From my perspective, this approach appears to be the most reasonable solution for supporting both 32-bit and 64-bit architectures.

@@ -411,8 +411,8 @@ static inline unsigned int s3c2410wdt_max_timeout(struct s3c2410_wdt *wdt)
 {
 	const unsigned long freq = s3c2410wdt_get_freq(wdt);
 
-	return S3C2410_WTCNT_MAXCNT / (freq / (S3C2410_WTCON_PRESCALE_MAX + 1)
-				       / S3C2410_WTCON_MAXDIV);
+	return S3C2410_WTCNT_MAXCNT / DIV_ROUND_UP(freq,
+		(S3C2410_WTCON_PRESCALE_MAX + 1) * S3C2410_WTCON_MAXDIV);
 }