Re: [PATCH] net: hix5hd2_gmac: avoid integer overload warning

Joe Perches
2015-10-16T21:22:15Z

On Fri, 2015-10-16 at 21:50 +0300, Sergei Shtylyov wrote:
> On 10/16/2015 09:04 PM, Joe Perches wrote:
>
> >>>> BITS_RX_EN is an 'unsigned long' constant, so the ones complement of that
> >>>> has bits set that do not fit into a 32-bit variable on 64-bit architectures,
> >>>> which causes a harmless gcc warning:
> >>> ...
> >>>> static void hix5hd2_port_disable(struct hix5hd2_priv *priv)
> >>>> {
> >>>> - writel_relaxed(~(BITS_RX_EN | BITS_TX_EN), priv->base + PORT_EN);
> >>>> + writel_relaxed(~(u32)(BITS_RX_EN | BITS_TX_EN), priv->base + PORT_EN);
> >>>> writel_relaxed(0, priv->base + DESC_WR_RD_ENA);
> >>>
> >>> ISTM that just means that the constants shouldn't be 'long'.
> >>
> >> Right, but that would probably mean changing the BIT() macro or not using it
> >> here. In the past I've argued against using that macro, but I've given
> >> up that fight.
> >
> > Fight on... (Somebody must have gone to USC here)
> >
> > There might be value in aefin BIT_U32 macro.
> > Maybe BIT_U64 too.
>
> There's BIT_ULL() already.

I know, but symmetry is good.
I think there'd be no harm in adding it.
Perhaps adding all the sized variants would be useful.

Something like:

#define BIT_OF_TYPE(type, nr) \
({ \
typeof(type) rtn; \
BUILD_BUG_ON(__builtin_constant_p(nr) && \
((nr) < 0 || \
(nr) >= sizeof(type) * BITS_PER_BYTE)); \
rtn = ((type)1) << (nr); \
rtn; \
})

#define BIT_U8(nr) BIT_OF_TYPE(u8, nr)
#define BIT_U16(nr) BIT_OF_TYPE(u16, nr)
#define BIT_U32(nr) BIT_OF_TYPE(u32, nr)
#define BIT_U64(nr) BIT_OF_TYPE(u64, nr)