linux-kernel - [RFC] hwmon: pwm_enable clarification

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Message-ID: <20241027174836.8588-1-derekjohn.clark@gmail.com>
Date: Sun, 27 Oct 2024 10:48:14 -0700
From: "Derek J. Clark" <derekjohn.clark@...il.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Jean Delvare <jdelvare@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Cryolita PukNgae <cryolitia@...il.com>,
	"Derek J . Clark" <derekjohn.clark@...il.com>,
	linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [RFC] hwmon: pwm_enable clarification

Greetings all,

I am working with Cryolita to fix up the GPD driver she submitted recently:
https://lore.kernel.org/all/20240718-gpd_fan-v4-0-116e5431a9fe@gmail.com/

We are currently having a discussion about the meaning of this part of the
documentation and are seeking some guidance from upstream.

> pwm[1-*]_enable
>     	Fan speed control method:
>     	0: no fan speed control (i.e. fan at full speed)
>     	1: manual fan speed control enabled (using pwm[1-*])
>     	2+: automatic fan speed control enabled
>     	Check individual chip documentation files for automatic mode
>     	details.
>     	RW

In oxp-sensors we took 0 to mean "no kernel control" so a setting of 0 is
technically "automatic" but fully controlled by the hardware with no
interaction from the driver. In her original driver draft she had taken this
literally to have the driver set the fan speed to 100% on this setting rather
then give back control to the hardware. My question is simply what is the
correct interpretation here? Ideally I would like to see this interface match
as existing userspace software is expecting 0 as hardware controlled and 1 as
manually controlled, but we also want to ensure this is correct before we
submit a v5.

Thank you for your time,
Derek