Re: [PATCH] ath9k: Add cast to u8 to FREQ2FBIN macro

From: Joe Perches
Date: Thu Apr 06 2017 - 22:37:18 EST


On Thu, 2017-04-06 at 16:54 -0700, Matthias Kaehlcke wrote:
> Hi Joe,
>
> El Thu, Apr 06, 2017 at 02:29:20PM -0700 Joe Perches ha dit:
>
> > On Thu, 2017-04-06 at 14:21 -0700, Matthias Kaehlcke wrote:
> > > The macro results are assigned to u8 variables/fields. Adding the cast
> > > fixes plenty of clang warnings about "implicit conversion from 'int' to
> > > 'u8'".
> > >
> > > Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> > > ---
> > > drivers/net/wireless/ath/ath9k/eeprom.h | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/wireless/ath/ath9k/eeprom.h b/drivers/net/wireless/ath/ath9k/eeprom.h
> > > index 30bf722e33ed..31390af6c33e 100644
> > > --- a/drivers/net/wireless/ath/ath9k/eeprom.h
> > > +++ b/drivers/net/wireless/ath/ath9k/eeprom.h
> > > @@ -106,7 +106,7 @@
> > > #define AR9285_RDEXT_DEFAULT 0x1F
> > >
> > > #define ATH9K_POW_SM(_r, _s) (((_r) & 0x3f) << (_s))
> > > -#define FREQ2FBIN(x, y) ((y) ? ((x) - 2300) : (((x) - 4800) / 5))
> > > +#define FREQ2FBIN(x, y) (u8)((y) ? ((x) - 2300) : (((x) - 4800) / 5))
> >
> > Maybe better to use:
> >
> > static inline u8 FREQ2FBIN(int x, int y)
> > {
> > if (y)
> > return x - 2300;
> > return (x - 4800) / 5;
> > }
>
> Thanks for your suggestion! Unfortunately in this case an inline
> function is not suitable since FREQ2FBIN() is mostly used for
> structure initialization:
>
> static const struct ar9300_eeprom ar9300_default = {
> ...
> .calFreqPier2G = {
> FREQ2FBIN(2412, 1),
> FREQ2FBIN(2437, 1),
> FREQ2FBIN(2472, 1)
> },
> ...

Maybe it's better to remove the second argument and write
something like:

#define FREQ2FBIN(x) \
(u8)(((x) >= 2300 && (x) <= 2555) ? (x) - 2300 : \
((x) >= 4800 && (x) <= 4800 + (256 * 5) ? ((x) - 4800) / 5) : \
__builtin_const_p(x) ? BUILD_BUG_ON(1) : 0)