Re: [PATCH 1/2] dt-bindings: hwmon: pwm-fan: Document start from dead stop properties

[Guenter Roeck <linux@roeck-us.net>]

On 11/5/24 05:52, Marek Vasut wrote:
> Delta AFC0612DB-F00 fan has to be set to at least 30% PWM duty cycle
> to spin up from a dead stop, and can be afterward throttled down to
> lower PWM duty cycle. Introduce support for operating such fans which

Doesn't this imply that a minimum pwm value is needed as well ?
Super-IO chips such as the NCT67xx series typically have two separate
registers, one for the pwm start value and one for the minimum pwm value.

> need to start at higher PWM duty cycle first and can slow down next.
> 
> Document two new DT properties, "fan-dead-stop-start-percent" and
> "fan-dead-stop-start-usec". The former describes the minimum percent
> of fan RPM at which it will surely spin up from dead stop. This value
> can be found in the fan datasheet and can be converted to PWM duty
> cycle easily. The "fan-dead-stop-start-usec" describes the minimum
> time in microseconds for which the fan has to be set to dead stop
> start RPM for the fan to surely spin up.
> 
> Signed-off-by: Marek Vasut <marex@denx.de>
> ---
> Cc: Conor Dooley <conor+dt@kernel.org>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Jean Delvare <jdelvare@suse.com>
> Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: devicetree@vger.kernel.org
> Cc: linux-hwmon@vger.kernel.org
> ---
>   Documentation/devicetree/bindings/hwmon/pwm-fan.yaml | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> index 4e5abf7580cc6..f1042471b5176 100644
> --- a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> @@ -31,6 +31,17 @@ properties:
>         it must be self resetting edge interrupts.
>       maxItems: 1
>   
> +  fan-dead-stop-start-percent:

Personally I don't think that "dead-stop" in the property name adds any value.
On the contrary, I think it leads to confusion. I head to read the description
to understand.


> +    description:
> +      Minimum fan RPM in percent to start from dead stop.

"to start when stopped" should be sufficient.

> +    minimum: 0
> +    maximum: 100
> +
> +  fan-dead-stop-start-usec:
> +    description:
> +      Time to wait in microseconds after start from dead stop.

Same as above for both name and description.

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
>     pulses-per-revolution:
>       description:
>         Define the number of pulses per fan revolution for each tachometer