Re: [PATCH 3/4] scsi: fix compiler warning for sg

[Sinan Kaya]

On 11/5/2015 2:56 PM, Andy Shevchenko wrote:
> On Thu, Nov 5, 2015 at 9:31 PM, Andy Shevchenko
> <andy.shevchenko@xxxxxxxxx> wrote:
> > On Thu, Nov 5, 2015 at 8:32 PM, Sinan Kaya <okaya@xxxxxxxxxxxxxx> wrote:
> > > On 11/5/2015 1:07 PM, Andy Shevchenko wrote:
> >
> > > Let's try again.
> > >
> > > static inline u64 mult_frac64(u64 x, u32 numer, u32 denom) {
> > >          u64 rem  = x % denom;
> > >          u64 quot = do_div(x, denom);
> > >          u64 mul = rem * numer;
> > >
> > >          return (quot * numer) + do_div(mul, denom);
> > > }
> >
> > First of all why not to put this to generic header? We have math64.h
> > and kernel.h.
> > Might be a good idea (needs to check current users) to move mult_frac
> > to math64.h.
> >
> > Then, x % y is already a problem. After all, you seems messed quot and
> > remainder.
> >
> > What about something like
> >
> > #if BITS_PER_LONG == 64
> >
> > #define mult_frac64(x,n,d)  mult_frac(x,n,d)
> >
> > #else
> >
> > static inline u64 mult_frac64(u64 x, u32 numer, u32 denom) {
> >          u64 r1 = do_div(x, denom);
> >          u64 r2 = r1 * numer;
> >
> >          do_div(r2, denom);
> >          return (x * numer) + r2;
> > }

I'll use this instead. This is cleaner, scalable and functionally 
correct to the original code. I'll post a patch with this soon.

> > #endif
> >
> > ?
>
> One more look to the users of MULDIV.
>
> They all seems 32 bit for x.
> It means you don't need two do_div()s at all.
>
> Just do something like:
>
> u64 d = x * numer;
> do_div(d, denom);
> return d;

--
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
Linux Foundation Collaborative Project
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