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

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Date:   Tue, 12 Sep 2017 18:22:11 +0200
From:   Rodolfo Giometti <giometti@...eenne.com>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     "discussions@...uxpps.org" <discussions@...uxpps.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Koen Vandeputte <koen.vandeputte@...ntric.com>
Subject: 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@...eenne.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@...-engineering.it
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