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

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Message-ID: <f50221fd-1d76-465b-ba53-62c08c6f8536@roeck-us.net>
Date: Sat, 22 Mar 2025 07:12:48 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Thomas Weißschuh <thomas@...ssschuh.net>,
 Sung-Chi Li <lschyi@...omium.org>
Cc: 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 3/22/25 06:55, Thomas Weißschuh wrote:
> On 2025-03-18 15:45:23+0800, Sung-Chi Li wrote:
>> The ChromeOS embedded controller (EC) supports closed loop fan speed
>> control, so add the fan target attribute under hwmon framework, such
>> that kernel can expose reading and specifying the desired fan RPM for
>> fans connected to the EC.
>>
>> When probing the cros_ec hwmon module, we also check the supported
>> command version of setting target fan RPM. This commit implements the
>> version 0 of getting the target fan RPM, which can only read the target
>> RPM of the first fan. This commit also implements the version 1 of
>> setting the target fan RPM to each fan respectively.
>>
>> Signed-off-by: Sung-Chi Li <lschyi@...omium.org>
>> ---
>> ChromeOS embedded controller (EC) supports closed-loop fan control. We
>> anticipate to have the fan related control from the kernel side, so this
>> series register the HWMON_F_TARGET attribute, and implement the read and
>> write function for setting/reading the target fan RPM from the EC side.
> 
> Should it be possible to switch back to automatic control?
> I can't find anything in the hwmon ABI about it.
> And neither in the CrOS EC source.
> 
> Am I missing something?
> 

Not sure I understand the context, but the fan control method is normally
selected with pwmX_enable, which is defined as

                 Fan speed control method:

                 - 0: no fan speed control (i.e. fan at full speed)
                 - 1: manual fan speed control enabled (using `pwmY`)
                 - 2+: automatic fan speed control enabled

Guenter