Re: [PATCH] pps-gpio: use IRQ edge config when not capturing both edges

[Rodolfo Giometti]

On 12/09/2017 17:54, Tim Harvey wrote:
> On Sun, Sep 10, 2017 at 3:43 AM, Rodolfo Giometti <giometti@xxxxxxxxxxxx> wrote:
> > On 08/09/2017 21:53, Tim Harvey wrote:
> > > PPS signals with very short pulse-widths can be missed if their state
> > > changes by the time the interrupt handler reads the GPIO pin state.
> > >
> > > To avoid this in the case where we are only looking for one edge we can
> > > use the edge configuration for the pin state but fall back to reading the
> > > pin if both edges are being watched.
> >
> >
> > I disagree. The "rising_edge" status should be get from the hardware and not
> > derived by an empirical computation. Or, at least, it should be specifically
> > activated by setting something like this:
> >
> >          pps {
> >                  pinctrl-names = "default";
> >                  pinctrl-0 = <&pinctrl_pps>;
> >
> >                  gpios = <&gpio1 26 GPIO_ACTIVE_HIGH>;
> >                  Yes-I-want-get-signal-status-in-an-epirical-way;
> >
> >                  compatible = "pps-gpio";
> >                  status = "okay";
> >          };
> >
> > This setting should also print a warning in order to be clear for the user
> > that he/she should know what he/she is doing.
> >
> > Then the code should check also the compatibility with property
> > "assert-falling-edge"...
>
> Hi Rodolfo,
>
> Do you agree with using the irq edge in general if/when it is
> available to resolve the case where small pulse-widths can be caught?
>
> I assumed because pps-gpio is the one configuring the irq based on
> info->capture_clear and info->assert_falling_edge that that it made
> sense to use that logic again when handling the interrupt but there is
> likely a call I can make to determine the irq (edge) type based on the
> irq.

If you get the information from the hardware it's OK for me, otherwise you 
should enable this behavior by using proper DT property.

Ciao,

Rodolfo

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