[PATCH 13/25] OMAP4: PM: Add WakeupGen module as OMAP gic_arch_extn

[Santosh]

On Wednesday 14 September 2011 10:38 PM, Tony Lindgren wrote:
> * Santosh<santosh.shilimkar at ti.com>  [110914 09:16]:
>>
>> First and foremost, I have to go with the approach here because MPUSS
>> hardware team put a requirement that GIC and wakeupgen should always be
>> kept in sync. If needed we can discuss this off-the list with Richard.
>>
>> Below is the extract from the veyron func specs.
>> -------------------------------------
>> Version 1.6 of veyron spec has this.
>>
>>  From page 95, paragraph 2 on version 1.6:
>>
>> "It is SW responsibility to program interrupt enabling/disabling
>> coherently in the GIC and in the Wugen enable registers. That is, a
>> given interrupt for a given CPU is either enable at both GIC and Wugen,
>> or disable at both, but no mix."
>> -------------------------------------
>>
>> The way understand this IP is, even in normal scenario's every IRQ
>> will come to wakeupgen and then it will pass that to GIC. CPU clock
>> domains are kept under HW supervised always and they can enter inactive
>> any time without WFI. Only wakeup gen can bring the CPU out of inactive
>> state.
>>
>> That's requirement really lead to this design choice. Just to add
>> all ARM SOC's using GIC has a gic extension interrupt controller and
>> follow the same approach for the secondary IRQCHIPO.
>
> Thanks for the clarification. It seems to me the spec is most likely
> wrong as we've had the GIC working for over two years now without
> doing anything with the wakeup gen registers :)
>
It's working because CPU clockdomain are never put under HW
supervised mode and they are kept in force wakeup. Clock-domain
never idles on mainline code. PM series will put the clock-domains
under HW supervison as needed to achieve any low power states and
then all sorts of corner cases will come out.

Regards
Santosh