[RFC] arm: use built-in byte swap function

[Kim Phillips]

On Wed, 20 Feb 2013 10:43:18 -0500
Nicolas Pitre <nico at fluxnic.net> wrote:

> On Wed, 20 Feb 2013, Woodhouse, David wrote:
> > On Wed, 2013-02-20 at 09:06 -0500, Nicolas Pitre wrote:
> > > ... in which case there is no harm shipping a .c file and trivially 
> > > enforcing -O2, the rest being equal.
> > 
> > For today's compilers, unless the wind changes.
> 
> We'll adapt if necessary.  Going with -O2 should remain pretty safe anyway.

Alas, not so for gcc 4.4 - I had forgotten I had tested
Ubuntu/Linaro 4.4.7-1ubuntu2 here:

https://patchwork.kernel.org/patch/2101491/

add -O2 to that test script and gcc 4.4 *always* emits calls to
__bswap[sd]i2, even with -march=armv6k+.

I'll try working on an assembly version given it probably
makes more sense, future-gcc-immunity-wise.

Otherwise we're back to the old 'if GCC_VERSION >= 40500' in
arch/arm/include/asm/swab.h...

Kim