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

On Tue, Feb 8, 2011 at 4:55 PM, Russell King - ARM Linux
[off-list ref] wrote:

On Tue, Feb 08, 2011 at 05:47:18PM +0100, Arnd Bergmann wrote:

quoted

On Tuesday 08 February 2011 17:25:16 Russell King - ARM Linux wrote:

quoted

On Tue, Feb 08, 2011 at 04:15:15PM +0100, Arnd Bergmann wrote:

quoted

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.

Can we represent the restriction in Kconfig somehow?

For example:

CPU_V6 depends on CPU_COMMON_V6PLUS
CPU_V7 depends on CPU_COMMON_V6PLUS
CPU_V5 depends on CPU_COMMON_V3_TO_V5
CPU_V4 depends on CPU_COMMON_V3_TO_V5
CPU_V3 depends on CPU_COMMON_V3_TO_V5

CPU_COMMON_V6PLUS depends on !CPU_COMMON_V3_TO_V5
CPU_COMMON_V3_TO_V5 depends on !CPU_COMMON_V6PLUS

...or something like that.

---Dave