Messages in this thread | | | Subject | Re: [PATCH] ARC: Fix __udelay parentheses | From | Joe Perches <> | Date | Wed, 28 Aug 2013 18:43:50 -0700 |
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On Wed, 2013-08-28 at 19:12 +0000, Mischa Jonker wrote: > 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?
I think the whole thing is odd and it should simply be
loops = loops_per_jiffy * usecs_to_jiffies(usecs);
and if it's really necessary to have a u64 delay then __delay should be rewritten to take an one as an argument and this calc should be:
u64 loops = (u64)loops_per_jiffy * usecs_to_jiffies(usecs);
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