linux-kernel - Re: [PATCH 2/2] pinctrl: renesas: rzg2l: Enable noise filter for GPIO interrupt input

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Date:   Wed, 20 Sep 2023 15:54:25 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Biju Das <biju.das.jz@...renesas.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>,
        Marc Zyngier <maz@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Biju Das <biju.das.au@...il.com>
Subject: Re: [PATCH 2/2] pinctrl: renesas: rzg2l: Enable noise filter for GPIO
 interrupt input

On Wed, Sep 20, 2023 at 2:37 PM Biju Das <biju.das.jz@...renesas.com> wrote:

> 2) Digital Noise Filter Clock Selection Register (FILCLKSEL):
>
> The FILCLKSEL register selects the divided clock to be input to digital noise filters.
>
> 00b: Not divided (initial value)
> 01b: Divided by 9000 (41.666 ns x 9000 = 375,000 ns)
> 10b: Divided by 18000 (41.666 ns x 18000 = 750,000 ns)
> 11b: Divided by 36000 (41.666 ns x 36000 = 1,500,000 ns)
> Note: This value is the value when the external clock is 24MHz.
>
> Q1) What is the recommended way to associate the above values with
>     PIN_CONFIG_INPUT_DEBOUNCE?
>
> Eg: I need to configure filter on, 8 stage filter , a divisor of 18000 for a mechanical button bounce noise.

As per the generic pin config and DT bindings:

 * @PIN_CONFIG_INPUT_DEBOUNCE: this will configure the pin to debounce mode,
 *      which means it will wait for signals to settle when reading inputs. The
 *      argument gives the debounce time in usecs. Setting the
 *      argument to zero turns debouncing off.

  input-debounce:
    $ref: /schemas/types.yaml#/definitions/uint32
    description: Takes the debounce time in usec as argument or 0 to disable
      debouncing

The recommended way is to pass the desired clock cycle in microseconds as the
argument to the pin config.

Yours,
Linus Walleij