Re: [PATCH v4 1/3] dt-bindings: hwmon: Add Microchip emc2305 support

[Krzysztof Kozlowski <krzk@kernel.org>]

On 14/03/2025 16:17, Guenter Roeck wrote:
>>>> +                pwms = <&fan_controller 1 1>;
>>>
>>> It's the same PWM for all fans? So isn't it basically one fan? How do you exactly control them independently, if the same PWM channel is used?
>>>
>>
>> It is the same PWM controller, but each fan has a different PWM channel. According to datasheet, the EMC2305 could control up to five programmable fan control circuits.
>> The driver will parse all fan child nodes during probe and use reg to differentiate the channels, similar as it is done on max6639 hwmon driver.
>> The 'pwms' arguments in the example are used to select the polarity and pwm output, which will be parsed in the driver to generate the bits for the registers used to select pwm output and pwm polarity.
>> (... <&fan_controller [pwm_polarity] [pwm_output]> ...).  Now, I realized that I should use: <&fan_controller [pwm_channel] [pwm_frequency] [pwm_polarity] [pwm_output]>. I will also document the arguments in #pwm-cells description.
>> Thanks!
>>
> 
> Please also document that the channel assignment is fixed. Technically it
> doesn't even make sense to specify the pwm channel (it is fixed and
> matches "reg"). I don't know if the channel number can be omitted from pwms.
> All you really need is polarity, frequency, and output type.
> 
> I am not really sure what to do if the channel number is mandatory.
> If it is, I'd suggest to document it as mandated but not needed/used,
> and then ignore it in the code.

Skipping channel would be fine for me, but then mention this in the
'reg' description.



Best regards,
Krzysztof