linux-kernel - Re: [PATCHv3] arm64: dts: meson: Enable active coling using gpio-fan on Odroid N2/N2+

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Date:   Sat, 22 Oct 2022 13:52:32 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Anand Moon <linux.amoon@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Dan Johansen <strit@...jaro.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3] arm64: dts: meson: Enable active coling using gpio-fan
 on Odroid N2/N2+

Hi Anand,

On Sat, Oct 22, 2022 at 1:27 PM Anand Moon <linux.amoon@...il.com> wrote:
[...]
> > > @@ -1982,7 +1982,6 @@ pwm_ao_d_10_pins: pwm-ao-d-10 {
> > >                                                 mux {
> > >                                                         groups = "pwm_ao_d_10";
> > >                                                         function = "pwm_ao_d";
> > > -                                                       bias-disable;
> > &pwm_ao_d_10_pins is not referenced anywhere so it seems that this
> > change has no impact on controlling the fan on Odroid-N2(+).
> > How did you test this change?
> >
> Ok I felt these changes affect the behavior of the pinctrl
>
>   * @PIN_CONFIG_BIAS_DISABLE: disable any pin bias on the pin, a
>  *  transition from say pull-up to pull-down implies that you disable
>  *  pull-up in the process, this setting disables all biasing.
>
> I mapped this is linked in pinctrl driver, pwm_ao_d_10_pins GPIOAO_10 see below
Yes, I understand this part.
My concern is: &pwm_ao_d_10_pins settings only become active when this
node is actively referenced. You can even see it in your output
below...

[...]
> pin 10 (GPIOAO_10): (MUX UNCLAIMED) aobus-banks:1958
This shows that it's used as a GPIO. If the &pwm_ao_d_10_pins setting
was used then it would show "function pwm_ao_d group pwm_ao_d_10"
(similar to what GPIOE_1 shows in your output)

If you want to know if a pull-up/down is enabled you can look at the output of:
$ cat /sys/kernel/debug/pinctrl/ff800000.sys-ctrl\:pinctrl@...pinctrl-meson/pinconf-pins
(I'm sure this can also be retrieved from some userspace tools, but I
don't know how)


Best regards,
Martin