From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [2.6.25 patch] drivers/crypto/hifn_795x.c: fix 64bit division
Date: Tue, 26 Feb 2008 22:47:19 -0800
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Cc: Evgeniy Polyakov <johnpol@2ka.mipt.ru>,
	Martin Michlmayr <tbm@cyrius.com>,
	linux-kernel@vger.kernel.org,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Ralf Baechle <ralf@linux-mips.org>,
	linux-crypto@vger.kernel.org
To: Adrian Bunk <bunk@kernel.org>
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On Wed, 27 Feb 2008 08:22:07 +0200 Adrian Bunk <bunk@kernel.org> wrote:

> On Tue, Feb 26, 2008 at 04:04:39PM -0800, Andrew Morton wrote:
> > On Tue, 26 Feb 2008 21:52:40 +0300 Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:
> > 
> > > Hi Adrian.
> > > 
> > > On Tue, Feb 26, 2008 at 05:34:21PM +0200, Adrian Bunk (bunk@kernel.org) wrote:
> > > > Using ndelay() with a 64bit variable as parameter can result in build 
> > > > errors like the following on some 32bit systems when it results in a 
> > > > 64bit division:
> > > > 
> > > > <--  snip  -->
> > > > 
> > > >  ...
> > > >   MODPOST 759 modules
> > > > ERROR: "__divdi3" [drivers/crypto/hifn_795x.ko] undefined!
> > > > 
> > > > <--  snip  -->
> > > > 
> > > > Reported by Martin Michlmayr.
> > > > 
> > > > Signed-off-by: Adrian Bunk <bunk@kernel.org>
> > > 
> > > Yep, ndelay() uses division, thanks a lot Adrian for spotting this.
> > 
> > hm.  Where?
> >...
> 
> include/linux/delay.h:35
> 

well found.

Something like this:


--- a/include/linux/delay.h~a
+++ a/include/linux/delay.h
@@ -7,10 +7,12 @@
  * Delay routines, using a pre-computed "loops_per_jiffy" value.
  */
 
-extern unsigned long loops_per_jiffy;
+#include <linux/kernel.h>
 
 #include <asm/delay.h>
 
+extern unsigned long loops_per_jiffy;
+
 /*
  * Using udelay() for intervals greater than a few milliseconds can
  * risk overflow for high loops_per_jiffy (high bogomips) machines. The
@@ -32,7 +34,11 @@ extern unsigned long loops_per_jiffy;
 #endif
 
 #ifndef ndelay
-#define ndelay(x)	udelay(((x)+999)/1000)
+static inline void ndelay(unsigned long x)
+{
+	udelay(DIV_ROUND_UP(x, 1000));
+}
+#define ndelay(x) ndelay(x)
 #endif
 
 void calibrate_delay(void);
_