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

From: John Stultz
Date: Mon Aug 03 2020 - 17:06:37 EST

On Tue, Jul 14, 2020 at 8:08 AM Douglas Anderson <dianders@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>

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.