linux-kernel - Re: [Y2038] [PATCH] fbdev: radeon: Remove 'struct timeval' usage

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Date:	Fri, 05 Jun 2015 23:12:14 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	y2038@...ts.linaro.org
Cc:	Tina Ruchandani <ruchandani.tina@...il.com>,
	Dave Airlie <airlied@...il.com>,
	Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>
Subject: Re: [Y2038] [PATCH] fbdev: radeon: Remove 'struct timeval' usage

On Friday 05 June 2015 00:55:05 Tina Ruchandani wrote:
> >>> +     hz = 1000000/delta;
> >
> > This needs to be on of the do_div family.
> >
> > Dave.
> 
> Hi Dave,
> I build-tested the patch for both 32-bit and 64-bit x86. If my
> understanding is correct, since the divisor is 64-bit here, the
> compiler will do "if (delta > 1000000) hz = 0; else hz =
> 1000000/(s32)delta" automatically?
> In general, is this a good thumb-rule to follow - use do_div if the
> dividend is 64-bit, and normal divide operator if only the divisor is
> 64-bit?
> 

I got a build error on 32-bit arm now. There is already a check
for an overflow of 10 seconds in there (10 million microseconds),
so it is safe to do the easiest fix is to cast that microsecond
value to a u32.

	Arnd
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