The majority of this patch was created by the following script:

***
ASM=arch/sparc/include/asm
mkdir -p $ASM
git mv include/asm-sparc64/ftrace.h $ASM
git rm include/asm-sparc64/*
git mv include/asm-sparc/* $ASM
sed -ie 's/asm-sparc64/asm/g' $ASM/*
sed -ie 's/asm-sparc/asm/g' $ASM/*
***

The rest was an update of the top-level Makefile to use sparc
for header files when sparc64 is being build.
And a small fixlet to pick up the correct unistd.h from
sparc64 code.
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

Used the following script to copy the files:
cd include
set -e
SPARC64=`ls asm-sparc64`
for FILE in ${SPARC64}; do
	if [ -f asm-sparc/$FILE ]; then
		echo $FILE exist in asm-sparc
	else
		git mv asm-sparc64/$FILE asm-sparc/$FILE
		printf "#include <asm-sparc/$FILE>\n" > asm-sparc64/$FILE
		git add asm-sparc64/$FILE
	fi
done
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

4096 will not fit into the immediate field of a compare instruction,
in fact it will end up being -4096 causing the check to fail every
time and thus disabling backoff.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

It can't be just empty, it has to at least branch
back to 'label'.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

When the cpu count is high and contention hits an atomic object, the
processors can synchronize such that some cpus continually get knocked
out and cannot complete the atomic update.

So implement an exponential backoff when SMP.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>