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

[Lina Iyer]

On Fri, Sep 20 2019 at 16:22 -0600, Stephen Boyd wrote:
> Quoting Lina Iyer (2019-09-11 09:15:57)
> > 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.
>
> Ok. I just wanted to confirm that masking "doesn't matter" to the PDC
> because it assumes the irqchip closer to the CPU will be able to mask it
> anyway. Is that right?
That is correct.