On Fri, 2015-05-22 at 15:57 +0000, David Laight wrote:
> From: Linuxppc-dev Christophe Leroy
> > Sent: 19 May 2015 16:19
> ...
> > diff --git a/arch/powerpc/include/asm/checksum.h
> > b/arch/powerpc/include/asm/checksum.h
> > index 5e43d2d..e8d9ef4 100644
> > --- a/arch/powerpc/include/asm/checksum.h
> > +++ b/arch/powerpc/include/asm/checksum.h
> > @@ -130,6 +130,22 @@ static inline __sum16 csum_tcpudp_magic(__be32 saddr,
> > __be32 daddr,
> > return csum_fold(csum_tcpudp_nofold(saddr, daddr, len, proto, sum));
> > }
> >
> > +#define HAVE_ARCH_CSUM_ADD
> > +static inline __wsum csum_add(__wsum csum, __wsum addend)
> > +{
> > +#ifdef __powerpc64__
> > + u64 res = (__force u64)csum;
> > +
> > + res += (__force u64)addend;
> > + return (__force __wsum)((u32)res + (res >> 32));
> > +#else
> > + asm("addc %0,%0,%1;"
> > + "addze %0,%0;"
> > + : "+r" (csum) : "r" (addend));
> > + return csum;
> > +#endif
>
> I'd have thought it better to test for the cpu type where you want the
> 'asm' variant, and then fall back on the C version for all others.
> I know (well suspect) there are only two cases here.
Usually it's more readable to see "if (x) ... else ..." than "if (!
x) ... else ..." and 64-bit is what has a symbol defined.
> I'd also have thought that the 64bit C version above would be generally
> 'good'.
It doesn't generate the addc/addze sequence. At least with GCC 4.8.2,
it does something like:
mr tmp0, csum
li tmp1, 0
li tmp2, 0
addc tmp3, addend, tmp0
adde csum, tmp2, tmp1
add csum, csum, tmp3
-Scott
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