Re: [PATCH v2 1/2] dt-bindings: hwmon: pwm-fan: Convert to DT schema

[Rob Herring]

On Tue, Apr 04, 2023 at 08:38:06PM +0300, Cristian Ciocaltea wrote:
> Convert the PWM fan bindings to DT schema format.
> 
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxxxxxx>
> ---
>  .../devicetree/bindings/hwmon/pwm-fan.txt     |  68 +---------
>  .../devicetree/bindings/hwmon/pwm-fan.yaml    | 119 ++++++++++++++++++
>  2 files changed, 120 insertions(+), 67 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.txt b/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> index 4509e688623a..48886f0ce415 100644
> --- a/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> @@ -1,67 +1 @@
> -Bindings for a fan connected to the PWM lines
> -
> -Required properties:
> -- compatible	: "pwm-fan"
> -- pwms		: the PWM that is used to control the PWM fan
> -- cooling-levels      : PWM duty cycle values in a range from 0 to 255
> -			which correspond to thermal cooling states
> -
> -Optional properties:
> -- fan-supply		: phandle to the regulator that provides power to the fan
> -- interrupts		: This contains an interrupt specifier for each fan
> -			  tachometer output connected to an interrupt source.
> -			  The output signal must generate a defined number of
> -			  interrupts per fan revolution, which require that
> -			  it must be self resetting edge interrupts. See
> -			  interrupt-controller/interrupts.txt for the format.
> -- pulses-per-revolution : define the number of pulses per fan revolution for
> -			  each tachometer input as an integer (default is 2
> -			  interrupts per revolution). The value must be
> -			  greater than zero.
> -
> -Example:
> -	fan0: pwm-fan {
> -		compatible = "pwm-fan";
> -		#cooling-cells = <2>;
> -		pwms = <&pwm 0 10000 0>;
> -		cooling-levels = <0 102 170 230>;
> -	};
> -
> -	thermal-zones {
> -		cpu_thermal: cpu-thermal {
> -			     thermal-sensors = <&tmu 0>;
> -			     polling-delay-passive = <0>;
> -			     polling-delay = <0>;
> -			     trips {
> -					cpu_alert1: cpu-alert1 {
> -						    temperature = <100000>; /* millicelsius */
> -						    hysteresis = <2000>; /* millicelsius */
> -						    type = "passive";
> -					};
> -			     };
> -			     cooling-maps {
> -					map0 {
> -						    trip = <&cpu_alert1>;
> -						    cooling-device = <&fan0 0 1>;
> -					};
> -			     };
> -		};
> -
> -Example 2:
> -	fan0: pwm-fan {
> -		compatible = "pwm-fan";
> -		pwms = <&pwm 0 40000 0>;
> -		fan-supply = <&reg_fan>;
> -		interrupt-parent = <&gpio5>;
> -		interrupts = <1 IRQ_TYPE_EDGE_FALLING>;
> -		pulses-per-revolution = <2>;
> -	};
> -
> -Example 3:
> -	fan0: pwm-fan {
> -		compatible = "pwm-fan";
> -		pwms = <&pwm1 0 25000 0>;
> -		interrupts-extended = <&gpio1 1 IRQ_TYPE_EDGE_FALLING>,
> -			<&gpio2 5 IRQ_TYPE_EDGE_FALLING>;
> -		pulses-per-revolution = <2>, <1>;
> -	};
> +This file has moved to pwm-fan.yaml.
> diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> new file mode 100644
> index 000000000000..048b6ea794c7
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> @@ -0,0 +1,119 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/hwmon/pwm-fan.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Fan connected to PWM lines
> +
> +maintainers:
> +  - Jean Delvare <jdelvare@xxxxxxxx>
> +  - Guenter Roeck <linux@xxxxxxxxxxxx>
> +
> +properties:
> +  compatible:
> +    const: pwm-fan
> +
> +  cooling-levels:
> +    description: PWM duty cycle values corresponding to thermal cooling states.
> +    items:
> +      maximum: 255
> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +
> +  fan-supply:
> +    description: Phandle to the regulator that provides power to the fan.
> +
> +  interrupts:
> +    description:
> +      This contains an interrupt specifier for each fan tachometer output
> +      connected to an interrupt source. The output signal must generate a
> +      defined number of interrupts per fan revolution, which require that
> +      it must be self resetting edge interrupts.
> +    minItems: 1
> +    maxItems: 5

I'm not so sure I'd allow for more than 1 if the example is the only 
case we can find. More than 1 implies you have multiple fans controlled 
by 1 PWM. What do you do with the tach data other than display it or 
detect a stuck fan. You can't really implement any control loop unless 
you average the rpm's? I suppose there could be h/w, so okay.

> +
> +  pulses-per-revolution:
> +    description:
> +      Define the number of pulses per fan revolution for each tachometer
> +      input as an integer.
> +    items:
> +      minimum: 1
> +      maximum: 4
> +      default: 2
> +    minItems: 1
> +    maxItems: 5
> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +
> +  pwms:
> +    description: The PWM that is used to control the fan.
> +    maxItems: 1
> +
> +  pwm-names: true

Not part of the original binding. It's not that useful in general if 
there's only 1 entry. It's completely useless if the name is not defined 
for the OS to use. So drop it.

> +
> +  "#cooling-cells":
> +    description:
> +      Must be 2, in order to specify minimum and maximum cooling state used in
> +      the cooling-maps reference. The first cell is the minimum cooling state
> +      and the second cell is the maximum cooling state requested.

Just duplicating the same text from thermal-cooling-devices.yaml is 
pointless.

> +    const: 2

As this is globally the only allowed value, you don't need to duplicate 
this either.

'"#cooling-cells": true"' is sufficient.

Rob