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

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  Re: [PATCH] pps-gpio: use IRQ edge config when not capturing both edges Tim Harvey <tharvey@gateworks.com> - 2017-09-12 18:00 +0200
    Re: [PATCH] pps-gpio: use IRQ edge config when not capturing both  edges Rodolfo Giometti <giometti@enneenne.com> - 2017-09-12 18:30 +0200

#1730972 — Re: [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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#1730991 — Re: [PATCH] pps-gpio: use IRQ edge config when not capturing both edges

On 12/09/2017 17:54, Tim Harvey wrote:
> 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.

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

-- 

HCE Engineering                      e-mail: giometti@hce-engineering.it
GNU/Linux Solutions                          giometti@enneenne.com
Linux Device Driver                          giometti@linux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
Cosino Project - the quick prototyping embedded system - www.cosino.it
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