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From:   Doug Anderson <dianders@chromium.org>
Date:   Fri, 11 Dec 2020 14:14:01 -0800
Message-ID: <CAD=FV=XvWFd84OxHmYgO8McV-ixe+ucMxhOdAWzHu4nLnnCtbQ@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] pinctrl: qcom: Clear possible pending irq when
 remuxing GPIOs
To:     Maulik Shah <mkshah@codeaurora.org>
Cc:     Rajendra Nayak <rnayak@codeaurora.org>,
        Marc Zyngier <maz@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Linus Walleij <linus.walleij@linaro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        Neeraj Upadhyay <neeraju@codeaurora.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Srinivas Ramana <sramana@codeaurora.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Andy Gross <agross@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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Hi,

On Thu, Dec 10, 2020 at 11:07 PM Maulik Shah <mkshah@codeaurora.org> wrote:
>
> I have slightly modified your test case (see at
> https://crrev.com/c/2584729) which is as per what i used in my testing.
>
> Here is what i am doing, setting GPIO to a fixed function (function 2 here)
> Note that function 0 is the GPIO (interrupt mode).
>
> 1) Pull up the GPIO in function 2
> 2) Pull down the GPIO in function 2
>
> Repeat above steps, and you will see fake interrupt every time pull down/up.
> This proves that if you mux away from GPIO then still PDC sees the line
> and can latch the interrupt at GIC.

Ah, super useful example!  Thanks!  Yes, I can replicate your results.

...but this seems to contradict my other test.  Ah, dang, I think I
see the problem with my original test.  The important difference is
that in your test you used the alternate function "mi2s_2" and in mine
I used "qspi_data".  When I selected "qspi_data" it must have been
actively driving the pin and _that's_ why I couldn't affect it.

When I change my test to use "mi2s_2" then my toggles via "wp enable"
and "wp disable" cause phantom interrupts.  That confirms what you're
saying: the PDC _can_ see the twiddles even when muxed away.
Presumably the active driving my "qspi_data" is also what caused my
phantom glitches.

So, as you said, that means my mental model is totally wrong here.
Wow, if I had known that earlier I would have saved a lot of time.
That'll learn me...

OK, v4 being posted and you can see if that handles all the cases?

-Doug