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

Arnd Bergmann
2015-10-16T21:42:32Z

On Friday 16 October 2015 14:22:15 Joe Perches wrote:
> 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)

Ok, I'll try:

Please stop this nonsense!

;-)

> > > 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)

As I said, I'd rather see less uses of BIT() instead of more. While
using 'BIT(23)' is often than the open-coded '1 << 23', I wish more
people would write that as '0x00800000' instead. It's easier to
match with data sheets, and to compare to printk output, plus
it's non-ambiguous if you are dealing with data sheets that use
the IBM convention of counting the bits from the other end.

Arnd