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

From: Linus Walleij <linus.walleij@linaro.org>
To: Douglas Anderson <dianders@chromium.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Rajendra Nayak <rnayak@codeaurora.org>,
	Maulik Shah <mkshah@codeaurora.org>,
	Marc Zyngier <maz@kernel.org>, Lina Iyer <ilina@codeaurora.org>,
	Cheng-Yi Chiang <cychiang@chromium.org>,
	Stephen Boyd <swboyd@chromium.org>,
	Andy Gross <agross@kernel.org>,
	MSM <linux-arm-msm@vger.kernel.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] pinctrl: qcom: Handle broken/missing PDC dual edge IRQs on sc7180
Date: Thu, 16 Jul 2020 15:42:54 +0200	[thread overview]
Message-ID: <CACRpkdasjuPXuooQj2fk=G097QR4oSSsoA-_d+vaH9aAKMgHeg@mail.gmail.com> (raw)
In-Reply-To: <20200714080254.v3.1.Ie0d730120b232a86a4eac1e2909bcbec844d1766@changeid>

On Tue, Jul 14, 2020 at 5:04 PM Douglas Anderson <dianders@chromium.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@chromium.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