linux-kernel - Re: [PATCH 04/10] hwmon: (amc6821) Add support for fan1_target and pwm1

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Message-ID: <e1933ae1-af38-4c17-b36e-33d43e90f057@cherry.de>
Date: Mon, 1 Jul 2024 13:23:56 +0200
From: Quentin Schulz <quentin.schulz@...rry.de>
To: Guenter Roeck <linux@...ck-us.net>, linux-hwmon@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Farouk Bouabid <farouk.bouabid@...rry.de>
Subject: Re: [PATCH 04/10] hwmon: (amc6821) Add support for fan1_target and
 pwm1_enable mode 4

Hi Guenter,

On 6/28/24 5:13 PM, Guenter Roeck wrote:
> After setting fan1_target and setting pwm1_enable to 4,
> the fan controller tries to achieve the requested fan speed.
> 

There's something in the docs (section `Software-RPM Control Mode (Fan 
Speed Regulator`) that rubs me the wrong way though.

"""
When the TACH-MODE bit (bit 1 of
0x02) is cleared ('0'), the duty cycle of PWM-Out is forced to 30% when 
the calculated desired value of duty
cycle is less than 30%. Therefore, the TACH setting must be not greater 
than the value corresponding to the
RPM for 30% duty cycle.
"""

TACH-MODE is never modified in the driver, so its default value prevails: 0.

I'm wondering if there isn't something we need to do to make sure we're 
not under those 30% for TACH-Low-Limit/TACH-High-Limit/TACH-SETTING? 
Forbid the user to write (or clamp instead) <30% duty cycle. Forbid the 
user to select mode 4 if current values are <30% duty cycle, or update 
them to be >=30%?

Otherwise, looking good to me,
Cheers,
Quentin