Re: [PATCH v2 1/3] kernel: Provide a __pow10() function

[Guenter Roeck]

On 5/7/19 2:49 PM, Florian Fainelli wrote:
> On 5/7/19 2:06 PM, Guenter Roeck wrote:
> > On Tue, May 07, 2019 at 12:35:02PM -0700, Florian Fainelli wrote:
> > > Provide a simple macro that can return the value of 10 raised to a
> > > positive integer. We are going to use this in order to scale units from
> > > firmware to HWMON.
> > >
> > > Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> > > ---
> > >   include/linux/kernel.h | 11 +++++++++++
> > >   1 file changed, 11 insertions(+)
> > >
> > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > > index 2d14e21c16c0..62fc8bd84bc9 100644
> > > --- a/include/linux/kernel.h
> > > +++ b/include/linux/kernel.h
> > > @@ -294,6 +294,17 @@ static inline u32 reciprocal_scale(u32 val, u32 ep_ro)
> > >   	return (u32)(((u64) val * ep_ro) >> 32);
> > >   }
> > >   
> > > +/* Return in f the value of 10 raise to the power x */
> > > +#define __pow10(x, f)(					\
> > > +{							\
> > > +	typeof(x) __x = abs(x);				\
> > > +	f = 1;						\
> > > +	while (__x--)					\
> > > +		f *= 10;				\
> > > +	f;						\
> > > +}							\
> > > +)
> >
> > Kind of unusual. I would have expected to use this like
> > 	f = __pow10(x);
> > ie without having to provide f as parameter. That would be much less
> > confusing. I assume this is to make the result type independent, but
> > I am not sure if that is worth the trouble.
>
> Correct, that was the intent here.
>
> > Are there users outside the hwmon code ? If not, it might be simpler
> > to keep it there for now.
>
> There appears to be a few outside actually:
>
> drivers/acpi/sbs.c::battery_scale
> drivers/iio/common/hid-sensors/hid-sensor-attributes.c::pow_10
>
> There could be others but those two came out as obvious candidates.
>
> Would you be okay with a local pow10 function within scmi-hwmon.c and a
> subsequent patch series providing a common function?

I would prefer that, actually, to reduce dependencies.

Thanks,
Guenter