linux-kernel - RE: [PATCH v3 2/2] powerpc: add support for csum

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB3D471@AcuExch.aculab.com>
Date:	Fri, 22 May 2015 15:57:38 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Christophe Leroy' <christophe.leroy@....fr>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	"Michael Ellerman" <mpe@...erman.id.au>,
	"scottwood@...escale.com" <scottwood@...escale.com>
CC:	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 2/2] powerpc: add support for csum_add()

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.

I'd also have thought that the 64bit C version above would be generally 'good'.

	David