netdev - [PATCH 1/2] net: Allow csum_sub() to be provided in arch

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Message-Id: <0c8eaab8f0685d2a70d125cf876238c70afd4fb6.1644574987.git.christophe.leroy@csgroup.eu>
Date:   Fri, 11 Feb 2022 11:24:48 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        netdev@...r.kernel.org
Subject: [PATCH 1/2] net: Allow csum_sub() to be provided in arch

In the same spirit as commit 07064c6e022b ("net: Allow csum_add to be
provided in arch"), allow csum_sub() to be provided by arch.

The generic implementation of csum_sub() call csum_add() with the
complement of the addendum.

Some architectures can do it directly.

This will also avoid getting several copies of csum_sub() outlined
when building with -Os.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 include/net/checksum.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/net/checksum.h b/include/net/checksum.h
index 9badcd5532ef..735d98724145 100644
--- a/include/net/checksum.h
+++ b/include/net/checksum.h
@@ -62,10 +62,12 @@ static inline __wsum csum_add(__wsum csum, __wsum addend)
 }
 #endif
 
+#ifndef HAVE_ARCH_CSUM_SUB
 static inline __wsum csum_sub(__wsum csum, __wsum addend)
 {
 	return csum_add(csum, ~addend);
 }
+#endif
 
 static inline __sum16 csum16_add(__sum16 csum, __be16 addend)
 {
-- 
2.34.1