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

[Dave Martin]

On Tue, Feb 8, 2011 at 4:55 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> 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.
>

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