Re: [PATCH RESEND v1 2/5] drivers: pinctrl: msm: enable PDC interrupt only during suspend

[Stephen Boyd]

Quoting Lina Iyer (2018-08-17 12:10:23)
> During suspend the system may power down some of the system rails. As a
> result, the TLMM hw block may not be operational anymore and wakeup
> capable GPIOs will not be detected. The PDC however will be operational
> and the GPIOs that are routed to the PDC as IRQs can wake the system up.
> 
> To avoid being interrupted twice (for TLMM and once for PDC IRQ) when a
> GPIO trips, use TLMM for active and switch to PDC for suspend. When
> entering suspend, disable the TLMM wakeup interrupt and instead enable
> the PDC IRQ and revert upon resume.

What about idle paths? Don't we want to disable the TLMM interrupt and
enable the PDC interrupt when the whole cluster goes idle so we get
wakeup interrupts? It's really unfortunate that the hardware can't
replay the interrupt from PDC to TLMM when it knows TLMM didn't get the
interrupt (because the whole chip was off) or the GIC didn't get the
summary irq (because the GIC was powered off). A little more hardware
effort would make this completely transparent to software and make TLMM
work across all low power modes.

Because of this complicated dance, it may make sense to always get the
interrupt at the PDC and then replay it into the TLMM chip "manually"
with the irq_set_irqchip_state() APIs. This way the duplicate interrupt
can't happen. The only way for the interrupt handler to run would be by
PDC poking the TLMM hardware to inject the irq into the status register.
I think with the TLMM that's possible if we configure the pin to have
the raw status bit disabled (so that edges on the physical line don't
latch into the GPIO interrupt status register) and the normal status bit
enabled (so that if the status register changes we'll interrupt the
CPU). It needs some testing to make sure that actually works though. If
it does work, then we have a way to inject interrupts on TLMM without
worry that the TLMM hardware will also see the interrupt.

Is there a good way to test an interrupt to see if it's edge or level
type configured? And is it really a problem to make PDC the hierarchical
parent of TLMM here so that PDC can intercept the type and wake state of
the GPIO irq? Plus there's the part where a GIC SPI interrupt runs for
some GPIO irq, and that needs to be decoded to figure out which GPIO it
is for and if it should be replayed or not. Maybe all types of GPIO irqs
can be replayed and if it's a level type interrupt we waste some time
handling the PDC interrupt just to do nothing besides forward what would
presumably already work without PDC intervention.