Re: [hwmon-next PATCH v4 3/4] hwmon: (adt7470) Expose fan control via PWM framework

[Uwe Kleine-König]

On Tue, Jul 28, 2026 at 10:56:04PM -0700, Guenter Roeck wrote:
> On 7/28/26 21:46, Luiz Angelo Daros de Luca wrote:
> > The ADT7470 features four PWM outputs designed to control fans.
> > Previously, these were only accessible through the legacy hwmon
> > sysfs interface.
> > 
> > Expose the ADT7470 fan control lines through the generic PWM framework.
> > This allows generic PWM consumers described in Device Tree, such as
> > "pwm-fan", to use the device through the "#pwm-cells" property.  This is
> > particularly necessary for boards where the ADT7470 external temperature
> > sensors are not populated and the chip is used strictly as a fan
> > controller (e.g., Edgecore ECS-2100-52T switches). In such setups,
> > delegating control to the generic PWM subsystem allows the kernel's
> > thermal framework to manage the fans based on unrelated temperature
> > zones, such as internal SoC sensors.
> > 
> > When a PWM consumer applies a new PWM state, the driver automatically
> > switches the corresponding PWM channel to manual mode so that the
> > requested duty cycle takes effect. The duty cycle specified by the PWM
> > framework is internally converted to the 0-255 scale expected by the
> > hardware registers.
> > 
> > The legacy sysfs interface remains unaffected and operates in parallel.
> 
> No, I won't accept this. It has to be either or. A pwm channel modeled as pwm
> subsystem channel must not be visible via hwmon attributes.

I didn't look in detail, but maybe my red line is a bit more lax. IMHO
it's not OK to be able to modify a setting that results from pushing
hwmon knobs using PWM operations or vice-versa. Switching between
exclusive use at runtime is IMHO ok.

Best regards
Uwe

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