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

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Date:   Sun, 10 Sep 2017 12:43:58 +0200
From:   Rodolfo Giometti <giometti@...eenne.com>
To:     Tim Harvey <tharvey@...eworks.com>,
        "discussions@...uxpps.org" <discussions@...uxpps.org>
Cc:     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 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"...

Ciao,

Rodolfo

-- 

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