linux-kernel - RE: [PATCH] ARC: Fix _

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Date:	Wed, 28 Aug 2013 19:12:22 +0000
From:	Mischa Jonker <Mischa.Jonker@...opsys.com>
To:	Joe Perches <joe@...ches.com>,
	Mischa Jonker <Mischa.Jonker@...opsys.com>
CC:	"Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] ARC: Fix __udelay parentheses

Hello Joe,

> I don't see the loops_per_jiffy initial shift << 32.

loops_per_jiffy * HZ = loops_per_second
loops_per_jiffy * HZ = 1,000,000 * loops_per_us
loops_per_jiffy * HZ * 4295 = 4,295,000 * loops_per_us

loops_per_jiffy * HZ * 4294.967296 = 2^32 * loops_per_us

> > > > -	loops = ((long long)(usecs * 4295 * HZ) *
> > > > -		 (long long)(loops_per_jiffy)) >> 32;
> > > > +	loops = (((long long) usecs) * 4295 * HZ *
> > > > +		  (long long) loops_per_jiffy) >> 32;

> 
> I know that.  It's the use of a signed long long vs the unsigned long long
> that I think wrong.

Yes that is wrong too.

> 
> Why cast a unsigned to a signed?

I don't know, this was in the original file. The issue that I was trying to solve, was that usleep didn't sleep long enough, and that is fixed by this patch. 

Wrt signed/unsigned: would you like me to update this patch or create a separate one?

Mischa
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