linux-kernel - Re: [PATCH 5/6] IIO:hwmon interface client driver.

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Date:	Mon, 24 Oct 2011 20:33:42 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Jonathan Cameron <jic23@....ac.uk>
Cc:	guenter.roeck@...csson.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linus.ml.walleij@...il.com" <linus.ml.walleij@...il.com>,
	"zdevai@...il.com" <zdevai@...il.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	"thomas.petazzoni@...e-electrons.com" 
	<thomas.petazzoni@...e-electrons.com>,
	"maxime.ripard@...e-electrons.com" <maxime.ripard@...e-electrons.com>
Subject: Re: [PATCH 5/6] IIO:hwmon interface client driver.

On Mon, Oct 24, 2011 at 04:58:49PM +0100, Jonathan Cameron wrote:
> On 10/24/11 16:39, Guenter Roeck wrote:
> > Is div_s64 really necessary, or would
> > 
> > 		result = (long)val * (long)scaleint +
> > 			DIV_ROUND_CLOSEST((s64)val * (s64)scalepart,
> > 					 1000000000LL);
> > 
> > work as well ?
> Not if you want it to compile on arm v5 by the look of it.
> 
> ERROR: "__aeabi_ldivmod" [drivers/staging/iio/iio_hwmon.ko] undefined!

You know, div64 is there to deal with the case of _sanely_ dividing
a 64-bit number by a 32-bit number - there should be absolutely no
question about _not_ using it if that's the operation you are wanting
to perform.

Expecting gcc to do a better job without using div64 is just asking for
bad code on 32-bit platforms.
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