On 10/05/24 15:36, Guenter Roeck wrote:
> Chris,
>
> On Thu, May 09, 2024 at 06:19:12PM +0000, Chris Packham wrote:
>> Hi Krzysztof,
>>
>> On 9/05/24 19:06, Krzysztof Kozlowski wrote:
>>> On 08/05/2024 23:55, Chris Packham wrote:
>>>> Add documentation for the pwm-initial-duty-cycle and
>>>> pwm-initial-frequency properties. These allow the starting state of the
>>>> PWM outputs to be set to cater for hardware designs where undesirable
>>>> amounts of noise is created by the default hardware state.
>>>>
>>>> Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
>>>> ---
>>>>
>>>> Notes:
>>>> Changes in v2:
>>>> - Document 0 as a valid value (leaves hardware as-is)
>>>>
>>>> .../devicetree/bindings/hwmon/adt7475.yaml | 27 ++++++++++++++++++-
>>>> 1 file changed, 26 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/hwmon/adt7475.yaml b/Documentation/devicetree/bindings/hwmon/adt7475.yaml
>>>> index 051c976ab711..97deda082b4a 100644
>>>> --- a/Documentation/devicetree/bindings/hwmon/adt7475.yaml
>>>> +++ b/Documentation/devicetree/bindings/hwmon/adt7475.yaml
>>>> @@ -51,6 +51,30 @@ properties:
>>>> enum: [0, 1]
>>>> default: 1
>>>>
>>>> + adi,pwm-initial-duty-cycle:
>>>> + description: |
>>>> + Configures the initial duty cycle for the PWM outputs. The hardware
>>>> + default is 100% but this may cause unwanted fan noise at startup. Set
>>>> + this to a value from 0 (0% duty cycle) to 255 (100% duty cycle).
>>>> + $ref: /schemas/types.yaml#/definitions/uint32-array
>>>> + minItems: 3
>>>> + maxItems: 3
>>>> + items:
>>>> + minimum: 0
>>>> + maximum: 255
>>>> + default: 255
>>>> +
>>>> + adi,pwm-initial-frequency:
>>> Frequency usually has some units, so use appropriate unit suffix and
>>> drop $ref. Maybe that's just target-rpm property?
>>>
>>> But isn't this duplicating previous property? This is fan controller,
>>> not PWM provider (in any case you miss proper $refs to pwm.yaml or
>>> fan-common.yaml), so the only thing you initially want to configure is
>>> the fan rotation, not specific PWM waveform. If you you want to
>>> configure specific PWM waveform, then it's a PWM provider... but it is
>>> not... Confused.
>> There's two things going on here. There's a PWM duty cycle which is
>> configurable from 0% to 100%. It might be nice if this was expressed as
>> a percentage instead of 0-255 but I went with the latter because that's
>> how the sysfs ABI for the duty cycle works.
>>
>> The frequency (which I'll call adi,pwm-initial-frequency-hz in v3)
>> affects how that duty cycle is presented to the fans. So you could still
>> have a duty cycle of 50% at any frequency. What frequency is best
>> depends on the kind of fans being used. In my particular case the lower
>> frequencies end up with the fans oscillating annoyingly so I use the
>> highest setting.
>>
> My udnerstanding is that we are supposed to use standard pwm provider
> properties. The property description is provider specicic, so I think
> we can pretty much just make it up.
>
> Essentially you'd first define a pwm provider which defines all the
> pwm parameters needed, such as pwm freqency, default duty cycle,
> and flags such as PWM_POLARITY_INVERTED. You'd then add something like
>
> pwms = <&pwm index frequency duty_cycle ... flags>;
>
> to the node for each fan, and be done.
>
> That doesn't mean that we would actually have to register the chip
> as pwm provider with the pwm subsystem; all we would have to do is to
> interpret the property values.
We've already got the pwm-active-state as a separate property so that
might be tricky to deal with, I guess it could be deprecated in favour
of something else. Looking at pwm.yaml and fan-common.yaml I can't quite
see how that'd help here. Were you thinking maybe something like
pwm: hwmon@2e {
compatible = "adi,adt7476";
reg = <0x2e>;
#pwm-cells = <4>;
fan-0 {
pwms = <&pwm 0 255 22500 PWM_POLARITY_INVERTED>;
pwm-names = "PWM1";
tach-ch = <0>;
};
fan-1 {
// controlled by pwm 0
tach-ch = <1>
};
fan-0 {
pwms = <&pwm 2 255 22500 PWM_POLARITY_INVERTED>;
pwm-names = "PWM3";
tach-ch <2>;
};
fan-1 {
// controlled by pwm 2
tach-ch = <3>
};
};
