Re: [PATCH 04/10] hwmon: (amc6821) Add support for fan1_target and pwm1_enable mode 4

Quentin Schulz
2024-07-01T11:24:01Z

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