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From: Michael Ellerman <mpe@ellerman.id.au>
To: Paul Mackerras <paulus@ozlabs.org>, linuxppc-dev@ozlabs.org
Subject: Re: [PATCH 1/2] powerpc/64: Fix checksum folding in
 csum_tcpudp_nofold and ip_fast_csum_nofold
In-Reply-To: <20161103051055.GA8368@fergus.ozlabs.ibm.com>
References: <20161103051055.GA8368@fergus.ozlabs.ibm.com>
Date: Fri, 02 Dec 2016 20:44:58 +1100
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Paul Mackerras <paulus@ozlabs.org> writes:

> These functions compute an IP checksum by computing a 64-bit sum and
> folding it to 32 bits (the "nofold" in their names refers to folding
> down to 16 bits).  However, doing (u32) (s + (s >> 32)) is not
> sufficient to fold a 64-bit sum to 32 bits correctly.  The addition
> can produce a carry out from bit 31, which needs to be added in to
> the sum to produce the correct result.
>
> To fix this, we copy the from64to32() function from lib/checksum.c
> and use that.

This collided with:

f9d4286b9516 ("arch/powerpc: Update parameters for csum_tcpudp_magic & csum_tcpudp_nofold")

Mind rebasing?

cheers