introduce HAVE_EFFICIENT_UNALIGNED_ACCESS Kconfig symbol

In many cases, especially in networking, it can be beneficial to know at
compile time whether the architecture can do unaligned accesses efficiently.
This patch introduces a new Kconfig symbol

	HAVE_EFFICIENT_UNALIGNED_ACCESS

for that purpose and adds it to the powerpc and x86 architectures.  Also add
some documentation about alignment and networking, and especially one intended
use of this symbol.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Ingo Molnar <mingo@elte.hu> [x86 architecture part]
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index a487671c282f..de6b49cd6be8 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -112,6 +112,7 @@ config PPC
         select HAVE_FTRACE
         select HAVE_IDE
         select HAVE_IOREMAP_PROT
+        select HAVE_EFFICIENT_UNALIGNED_ACCESS
         select HAVE_KPROBES
         select HAVE_ARCH_KGDB
         select HAVE_KRETPROBES