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SubjectRe: [PATCH] pps-gpio: use IRQ edge config when not capturing both edges
On Sun, Sep 10, 2017 at 3:43 AM, Rodolfo Giometti <giometti@enneenne.com> 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.

Tim

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