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References: <20230531151918.105223-1-nick.hawkins@hpe.com> <20230531151918.105223-3-nick.hawkins@hpe.com>
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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Thu, 1 Jun 2023 13:39:37 +0200
Message-ID: <CACRpkdaH2eZSCtEdCw+S1eGVrPBdEo83gbSf2wzu3-p0=P+CmQ@mail.gmail.com>
Subject: Re: [PATCH v2 2/5] gpio: gxp: Add HPE GXP GPIO
To:     nick.hawkins@hpe.com
Cc:     verdun@hpe.com, brgl@bgdev.pl, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, jdelvare@suse.com,
        linux@roeck-us.net, andy.shevchenko@gmail.com,
        linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org
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Hi Nick,

thanks for your patch!

On Wed, May 31, 2023 at 5:23=E2=80=AFPM <nick.hawkins@hpe.com> wrote:

> +/* Provide info for fan driver */
> +u8 fan_presence;
> +EXPORT_SYMBOL(fan_presence);
> +
> +u8 fan_fail;
> +EXPORT_SYMBOL(fan_fail);
> +
> +/* Remember last PSU config */
> +u8 psu_presence;

As Bartosz said this doesn't work.

to me it looks like you should define a GPIO-controlled fan in the
device tree, similar to this:

       fan0: gpio-fan {
                compatible =3D "gpio-fan";
                gpios =3D <&gpio1 6 GPIO_ACTIVE_HIGH>;
                gpio-fan,speed-map =3D <0 0>, <10000 1>;
                #cooling-cells =3D <2>;
        };

Then that cooling cell should be used by a thermal driver for the chassis
to keep the temperature reasonable. I bet you have a temperature sensor
as well, meaning they should form a thermal zone controlled by the fan.

Examples of chassis thermal zones in device tree:
arch/arm/boot/dts/gemini-dlink-dir-685.dts
arch/arm/boot/dts/gemini-dlink-dns-313.dts

Yours,
Linus Walleij