linux-kernel - Re: [PATCH v3] pinctrl: qcom: Handle broken/missing PDC dual edge IRQs on sc7180

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Date:   Mon, 3 Aug 2020 14:06:24 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>, rnayak@...eaurora.org,
        mkshah@...eaurora.org, Marc Zyngier <maz@...nel.org>,
        ilina@...eaurora.org, cychiang@...omium.org,
        Stephen Boyd <swboyd@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-gpio@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Todd Kjos <tkjos@...gle.com>,
        Amit Pundir <amit.pundir@...aro.org>
Subject: Re: [PATCH v3] pinctrl: qcom: Handle broken/missing PDC dual edge
 IRQs on sc7180

On Tue, Jul 14, 2020 at 8:08 AM Douglas Anderson <dianders@...omium.org> wrote:
>
> Depending on how you look at it, you can either say that:
> a) There is a PDC hardware issue (with the specific IP rev that exists
>    on sc7180) that causes the PDC not to work properly when configured
>    to handle dual edges.
> b) The dual edge feature of the PDC hardware was only added in later
>    HW revisions and thus isn't in all hardware.
>
> Regardless of how you look at it, let's work around the lack of dual
> edge support by only ever letting our parent see requests for single
> edge interrupts on affected hardware.
>
> NOTE: it's possible that a driver requesting a dual edge interrupt
> might get several edges coalesced into a single IRQ.  For instance if
> a line starts low and then goes high and low again, the driver that
> requested the IRQ is not guaranteed to be called twice.  However, it
> is guaranteed that once the driver's interrupt handler starts running
> its first instruction that any new edges coming in will cause the
> interrupt to fire again.  This is relatively commonplace for dual-edge
> gpio interrupts (many gpio controllers require software to emulate
> dual edge with single edge) so client drivers should be setup to
> handle it.
>
> Fixes: e35a6ae0eb3a ("pinctrl/msm: Setup GPIO chip in hierarchy")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Just as a heads up. I started seeing boot failures (crashes really
early before we get serial output) with db845c when testing with the
android-mainline tree that pulled v5.8 in.
I did some quick bisection and came down to this patch, and sure
enough things boot again with this patch reverted.

In my testing earlier today with v5.8 (+ just a few patches for db845c
support), I didn't see this failure, but the configs in use are
different there.

I'll try to spend a bit of time to understand exactly what is failing,
but if you have any initial suggestions for things to try, I'd
appreciate it.

thanks
-john