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

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Date:   Thu, 16 Jul 2020 15:42:54 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rajendra Nayak <rnayak@...eaurora.org>,
        Maulik Shah <mkshah@...eaurora.org>,
        Marc Zyngier <maz@...nel.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Cheng-Yi Chiang <cychiang@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Andy Gross <agross@...nel.org>,
        MSM <linux-arm-msm@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] pinctrl: qcom: Handle broken/missing PDC dual edge
 IRQs on sc7180

On Tue, Jul 14, 2020 at 5:04 PM 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>
> ---
> As far as I can tell everything here should work and the limited
> testing I'm able to give it shows that, in fact, I can detect both
> edges.
>
> I specifically left off Reviewed-by and Tested-by tags from v2 becuase
> I felt that the implementation had changed just enough to invalidate
> previous reviews / testing.  Hopefully it's not too much of a hassle
> for folks to re-review and re-test.
>
> Changes in v3:
> - Rate limit the warning.

Tentatively applied this to the fixes branch in the pinctrl tree
so we get some linux-next coverage.

Would be nice to get Bjorn's ACK on it as well!

Yours,
Linus Walleij