[PATCH 4/5] ARM: scu: Move register defines to header file

On Tue, Jan 25, 2011 at 12:56:56PM +0000, Russell King - ARM Linux wrote:

On Tue, Jan 25, 2011 at 06:06:27PM +0530, Santosh Shilimkar wrote:

quoted

Ok. I missed some information my last email.
The SCU power status programming is used to take CPU in/out
of coherency as an alternative to SMP bit. We don't
have an access to SMP bit on OMAP4. ARM has already
confirmed SCU programming is same as SMP bit enable/disable.

I don't know how safe is to use spin lock when one CPU is
goes out of coherency after programming the power state. The
spin lock release may not even be visible to other CPU.

Erm, I do hope that's not the case, as that means it is unsafe for CPUs in
a SMP system to write to this register without them potentially trampling
over each other.

If it is the case, then the solutions are either:
1. Fix the hardware so that coherency requests only yet turned off
   when entering the WFI state.
2. Fix the hardware such that each CPU has a separate register.

Actually, we can do this safely - byte stores are permitted to SCU
registers probably for this very reason.