Re: [PATCH RFC 02/14] drivers: irqchip: pdc: Do not toggle IRQ_ENABLE during mask/unmask

[Lina Iyer]

On Thu, Sep 05 2019 at 18:39 -0600, Stephen Boyd wrote:
> Quoting Lina Iyer (2019-08-29 11:11:51)
> > When an interrupt is to be serviced, the convention is to mask the
> > interrupt at the chip and unmask after servicing the interrupt. Enabling
> > and disabling the interrupt at the PDC irqchip causes an interrupt storm
> > due to the way dual edge interrupts are handled in hardware.
> >
> > Skip configuring the PDC when the IRQ is masked and unmasked, instead
> > use the irq_enable/irq_disable callbacks to toggle the IRQ_ENABLE
> > register at the PDC. The PDC's IRQ_ENABLE register is only used during
> > the monitoring mode when the system is asleep and is not needed for
> > active mode detection.
>
> I think this is saying that we want to always let the line be sent
> through the PDC to the parent irqchip, in this case GIC, so that we
> don't get an interrupt storm for dual edge interrupts? Why does dual
> edge interrupts cause a problem?
I am not sure about the hardware details, but the PDC designers did not
expect enable and disable to be called whenever the interrupt is
handled. This specially becomes a problem for dual edge interrupts which
seems to generate a interrupt storm when enabled/disabled while handling
the interrupt.

--Lina