[PATCH 13/14] powerpc/64: runlatch CTRL[RUN] set optimisation

[Michael Ellerman]

Benjamin Herrenschmidt <benh at kernel.crashing.org> writes:

> On Tue, 2017-06-13 at 20:04 +1000, Michael Ellerman wrote:
>> > Good idea.  Writing to CTRL register can change only the RUN field.
>> > Was this any different in older generations?
>> 
>> No AFAICS back to 2.02.
>> 
>> > Anton and Ben kept the mfspr/mtspr part in earlier updates to this
>> > routine.
>> 
>> Doing the read/modify write is forward compatible vs a new writable
>> field, whereas writing the whole register with a known value is not.
>
> At this stage I wouldn't worry too much about it. What we can do is
> write a pre-cooked value (from reading it earlier once at boot) if we
> are paranoid or just do what Nick does and put the onus on future
> designs that might want to re-use it for other things to add a mode
> bits to configure the new feature in.

Fine by me.

cheers