linux-kernel - Re: [PATCH v3] hwmon: (cros_ec) Add set and get target fan RPM function

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Message-ID: <Z-NqFTZuW5yJ_FC5@google.com>
Date: Wed, 26 Mar 2025 02:44:37 +0000
From: Sung-Chi Li <lschyi@...omium.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Thomas Weißschuh <thomas@...ssschuh.net>,
	Jean Delvare <jdelvare@...e.com>,
	Benson Leung <bleung@...omium.org>,
	Guenter Roeck <groeck@...omium.org>,
	chrome-platform@...ts.linux.dev, linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] hwmon: (cros_ec) Add set and get target fan RPM
 function

On Tue, Mar 25, 2025 at 05:55:07AM -0700, Guenter Roeck wrote:
> On 3/25/25 00:16, Sung-Chi Li wrote:
> 
> > 
> > Currently, when sending the fan control setting to EC, EC will switch to manual
> > fan control automatically. When system suspends or shuts down, fans are going
> > back to automatic control (based on current EC implementation).
> > 
> > Do you mean the driver should not change the fan control method if there is no
> > pwmY_enable implemented, or it is the user that should first explicitly set the
> > fan to manualy mode, then the user can specify the desired fan speed?
> 
> The user should first set the fan control method to manual mode.
> 
> Unless I am missing something, setting manual mode means that pwmY_enable does have
> to be implemented.
> 
> Note that the suspend/resume behavior is unexpected. The user would assume that the fan
> control method is still in the same mode after resume. If resume reverts to automatic mode,
> there should be a suspend/resume handler which restores the mode on resume.
> 
> Thanks,
> Guenter
> 

Thank you for the clarification, I think it is better to implement some missing
EC control points (For 1. getting a fan PWM value, and 2. for getting individual
fan target speed) first. After that, I will continue working on this seris.
Thanks all for these details that I missed.