[PATCH v2] ARM: Define wfi() macro for v6 processors

[Russell King - ARM Linux]

On Tue, Feb 08, 2011 at 05:47:18PM +0100, Arnd Bergmann wrote:
> On Tuesday 08 February 2011 17:25:16 Russell King - ARM Linux wrote:
> > On Tue, Feb 08, 2011 at 04:15:15PM +0100, Arnd Bergmann wrote:
> > > But that doesn't work if you build a combined v5/v6/v7 kernel, because
> > > v5 supports neither form, right? I think to do that, it needs the
> > > same kind of abstraction that we have for a number of other things
> > > like cache management in arch/arm/mm/.
> > 
> > The options are kernels which support v3-v5 or v6-v7.  There's too big
> > a change between v5 and v6 to combine those into one kernel.
> 
> Ah, good to know. I never realized this with the common binary discussions.
> Building for the versatile/realview platform makes it possible to select
> any of ARM926 and the v6/v6k/v7 CPUs, as well as ARM7TDMI in the same
> kernel config, so I assumed that this was actually a valid configuration
> aside from bugs.
> 
> Would an attempt to make a combined v5/v6 kernel result in unacceptably
> bad code, or is this just too much work for anyone to be bothered with
> and little practical value?

If you build for anything less than v6, you lose all barriers, the icache
synchronization, and proper atomic operations.  Just to name a few.