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Date:   Wed, 11 Sep 2019 10:15:57 -0600
From:   Lina Iyer <ilina@codeaurora.org>
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     evgreen@chromium.org, linus.walleij@linaro.org,
        marc.zyngier@arm.com, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, bjorn.andersson@linaro.org,
        mkshah@codeaurora.org, linux-gpio@vger.kernel.org,
        rnayak@codeaurora.org
Subject: Re: [PATCH RFC 02/14] drivers: irqchip: pdc: Do not toggle
 IRQ_ENABLE during mask/unmask
Message-ID: <20190911161557.GB30053@codeaurora.org>
References: <20190829181203.2660-1-ilina@codeaurora.org>
 <20190829181203.2660-3-ilina@codeaurora.org>
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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