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

[Sinan Kaya]

On 11/5/2015 3:48 AM, Andy Shevchenko wrote:
> On Thu, Nov 5, 2015 at 6:46 AM, Sinan Kaya <okaya@xxxxxxxxxxxxxx> wrote:
> > The MULDIV macro has been designed for small
> > numbers. It emits an overflow warning on 64 bit
> > systems. This patch places type casts in the
> > parameters to fix the compiler warning.
> >
> > Signed-off-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
> > ---
> >   drivers/scsi/sg.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> > index 9d7b7db..eb2739d 100644
> > --- a/drivers/scsi/sg.c
> > +++ b/drivers/scsi/sg.c
> > @@ -88,7 +88,10 @@ static void sg_proc_cleanup(void);
> >    * Of course an overflow is inavoidable if the result of muldiv doesn't fit
> >    * in 32 bits.
> >    */
> > -#define MULDIV(X,MUL,DIV) ((((X % DIV) * MUL) / DIV) + ((X / DIV) * MUL))
> > +static inline u64 MULDIV(u64 X, u32 MUL, u32 DIV)
> > +{
> > +       return ((((X % DIV) * MUL) / DIV) + ((X / DIV) * MUL));
> > +}
>
> Like kbuild bot already told you it would be nice to think of 32-bit
> architectures.
>
> Moreover we have mult_frac() macro already for 32-bit numbers.
>
> For 64 bit numbers you need to do do_div().
>
> Like:
>
> static inline u64 mult_frac64(u64 x, u32 m, u32 n)
> {
> u64 ret;
>
> ret = do_div(x, n);
> return ret * m;
> }

OK, I didn't know that we had such a macro. To make this look like the 
other macro, I can do this.

static inline u64 mult_frac64(u64 x, u32 numer, u32 denom)
{
	u64 quot;
	u64 rem  = x % denom;
	u64 rem2;

	quot = x;
	do_div(quot, denom);

	rem2 = rem * numer;
	do_div(rem2, denom);

	return (quot * numer) + rem2;
}

#define MULDIV(X,MUL,DIV)	mult_frac64(X, MUL, DIV)

> >   #define SG_DEFAULT_TIMEOUT MULDIV(SG_DEFAULT_TIMEOUT_USER, HZ, USER_HZ)
> >
> > --
> > 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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--
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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