Re: [PATCH v4 1/2] dt-bindings: hwmon: pwm-fan: Document default-pwm property

Guenter Roeck
2025-01-06T18:32:31Z

On 1/6/25 09:38, Rob Herring wrote:

>> The minimum PWM is presumably 0, E.G. signal always low?
>
> I'm talking about the duty cycle needed to start the fan spinning and to
> keep it spinning. I'm sure that value is not 1 for any fan except one in
> a physics textbook (the only place friction does not exist).
>
> Maybe the minimum is index 0 of cooling-levels?
>

Fan controllers often have a separate value for the lowest cooling level
and for the PWM necessary to start a fan. The pwm associated with the lowest
cooling level may be lower than the pwm necessary to start a fan.

The fan controller would start a fan by applying the "start fan" pwm value
for a period of time, then reduce the pwm to the desired pwm value for
the running fan.

I'll be happy to dig up datasheet references if needed.

Guenter