linux-kernel - Re: [PATCH v2 2/5] gpio: gxp: Add HPE GXP GPIO

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Date:   Thu, 1 Jun 2023 13:39:37 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     nick.hawkins@....com
Cc:     verdun@....com, brgl@...ev.pl, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, jdelvare@...e.com,
        linux@...ck-us.net, andy.shevchenko@...il.com,
        linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org
Subject: Re: [PATCH v2 2/5] gpio: gxp: Add HPE GXP GPIO

Hi Nick,

thanks for your patch!

On Wed, May 31, 2023 at 5:23 PM <nick.hawkins@....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 = "gpio-fan";
                gpios = <&gpio1 6 GPIO_ACTIVE_HIGH>;
                gpio-fan,speed-map = <0 0>, <10000 1>;
                #cooling-cells = <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