linux-kernel - Re: [PATCH RFC 02/14] drivers: irqchip: pdc: Do not toggle IRQ

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Message-ID: <5d71aad9.1c69fb81.f469e.262f@mx.google.com>
Date:   Thu, 05 Sep 2019 17:39:52 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Lina Iyer <ilina@...eaurora.org>, evgreen@...omium.org,
        linus.walleij@...aro.org, marc.zyngier@....com
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        bjorn.andersson@...aro.org, mkshah@...eaurora.org,
        linux-gpio@...r.kernel.org, rnayak@...eaurora.org,
        Lina Iyer <ilina@...eaurora.org>
Subject: Re: [PATCH RFC 02/14] drivers: irqchip: pdc: Do not toggle IRQ_ENABLE during mask/unmask

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?

> 
> Signed-off-by: Lina Iyer <ilina@...eaurora.org>