Re: (EXT) Re: [PATCH v2 1/1] hwmon: pwm-fan: dynamically switch regulator

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Hello Guenter,

Am Freitag, 6. Mai 2022, 00:00:37 CEST schrieb Guenter Roeck:
> On Wed, May 04, 2022 at 02:45:51PM +0200, Alexander Stein wrote:
> > From: Markus Niebel <Markus.Niebel@ew.tq-group.com>
> > 
> > A pwm value equal to zero is meant to switch off the pwm
> > hence also switching off the fan. Currently the optional
> > regulator is always on. When using this driver on boards
> > with an inverted pwm signal polarity this can cause running
> > the fan at maximum speed when setting pwm to zero.
> 
> The appropriate solution in this case would be to tell the
> software that the pwm is inverted. Turning off the regulator
> in that situation is a bad idea since setting the pwm value to
> 1 would set it to almost full speed. That does not really make
> sense.

The pwm-fan driver is already configured for inverted PWM (ommited some 
properties for shortness):
fan0: pwm-fan {
	compatible = "pwm-fan";
	fan-supply = <&reg_pwm_fan>;
	pwms = <&pwm3 0 40000 PWM_POLARITY_INVERTED>;
	cooling-levels = <0 32 64 128 196 240>;
[...]
};

The problem here is that the pwm-fan driver currently enables the regulator 
unconditionally, but the PWM only when the fan is enabled, refer to 
__set_pwm(). This results in a fan at full speed when pwm-fan is idle, as pwm 
state is not enabled.
If you keep the regulator enabled all the time, you have to drive the PWM at 
full duty to get an idle fan, which seems insensible for me in regards to 
power consumption. To implement this PWM enable inversion in pwm-fan driver 
seems even more complex to me.
I also don't see any problem when disabling the regulator of the PWM fan. If 
the regulator is disabled, the fan won't move at all, regardless of PWM duty.
That's why I favor to disable the regulator for the fan when it is idle.

I hope this clarifies the motivation for this change.

Best regards,
Alexander

> > The proposed changes switch the regulator off, when PWM is
> > currently enabled but pwm is requested to set to zero
> > and switch der regulator on, when PWM is currently disabled
> > but pwm shall be set to a no zero value.
> > 
> > Add __set_pwm_and_regulator and rewrite __set_pwm to
> > handle regulator switching for the following conditions:
> > 
> > - probe: pwm duty -> max, pwm state is unkwown: use __set_pwm
> > 
> >   and enable regulator separately to keep the devm action
> > 
> > - off: new pwm duty is zero, pwm currently enabled: disable
> > 
> >   regulator
> > 
> > - on: new pwm duty is non zero, pwm currently disabled: enable
> > 
> >   regulator
> > 
> > Signed-off-by: Markus Niebel <Markus.Niebel@ew.tq-group.com>
> > Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> > ---
> > Changes in v2:
> > * Added my own missing S-o-b
> > 
> >  drivers/hwmon/pwm-fan.c | 144 ++++++++++++++++++++++++++--------------
> >  1 file changed, 93 insertions(+), 51 deletions(-)
> > 
> > diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> > index f12b9a28a232..b47d59fbe836 100644
> > --- a/drivers/hwmon/pwm-fan.c
> > +++ b/drivers/hwmon/pwm-fan.c
> > @@ -97,18 +97,50 @@ static int  __set_pwm(struct pwm_fan_ctx *ctx,
> > unsigned long pwm)> 
> >  	unsigned long period;
> >  	int ret = 0;
> >  	struct pwm_state *state = &ctx->pwm_state;
> > 
> > +	/* track changes of reg_en for error handling */
> > +	enum regulator_change {
> > +		untouched,
> > +		enabled,
> > +		disabled,
> > +	} reg_change = untouched;
> > 
> >  	mutex_lock(&ctx->lock);
> > 
> > +
> > 
> >  	if (ctx->pwm_value == pwm)
> >  	
> >  		goto exit_set_pwm_err;
> > 
> > +	if (ctx->reg_en) {
> > +		if (pwm && !state->enabled) {
> > +			reg_change = enabled;
> > +			ret = regulator_enable(ctx->reg_en);
> > +		} else if (!pwm && state->enabled) {
> > +			reg_change = disabled;
> > +			ret = regulator_disable(ctx->reg_en);
> > +		}
> > +		if (ret)
> > +			goto exit_set_pwm_err;
> > +	}
> > +
> > 
> >  	period = state->period;
> >  	state->duty_cycle = DIV_ROUND_UP(pwm * (period - 1), MAX_PWM);
> >  	state->enabled = pwm ? true : false;
> >  	
> >  	ret = pwm_apply_state(ctx->pwm, state);
> > 
> > -	if (!ret)
> > +	if (!ret) {
> > 
> >  		ctx->pwm_value = pwm;
> > 
> > +	} else if (reg_change != untouched) {
> > +		/*
> > +		 * revert regulator changes to keep consistency between
> > +		 * pwm and regulator
> > +		 */
> > +		int err;
> > +
> > +		if (reg_change == enabled)
> > +			err = regulator_disable(ctx->reg_en);
> > +		else if (reg_change == disabled)
> > +			err = regulator_enable(ctx->reg_en);
> > +	}
> > +
> > 
> >  exit_set_pwm_err:
> >  	mutex_unlock(&ctx->lock);
> >  	return ret;
> > 
> > @@ -280,18 +312,50 @@ static int pwm_fan_of_get_cooling_data(struct device
> > *dev,> 
> >  	return 0;
> >  
> >  }
> > 
> > -static void pwm_fan_regulator_disable(void *data)
> > +/*
> > + * disable fan and regulator
> > + * if cleanup is true, disable pwm regardless of regulator disable result
> > + * this makes the function dual use for unloading driver and suspend
> > + */
> > +
> > +static int __pwm_fan_disable_or_cleanup(struct pwm_fan_ctx *ctx, bool
> > cleanup)> 
> >  {
> > 
> > -	regulator_disable(data);
> > +	int ret;
> > +
> > +	if (ctx->pwm_value) {
> > +		/* keep ctx->pwm_state unmodified for pwm_fan_resume() 
*/
> > +		struct pwm_state state = ctx->pwm_state;
> > +
> > +		/* regulator is only enabled if pwm_value is not zero */
> > +		if (ctx->pwm_value && ctx->reg_en) {
> > +			ret = regulator_disable(ctx->reg_en);
> > +			if (ret) {
> > +				pr_err("Failed to disable fan 
supply: %d\n", ret);
> > +				if (!cleanup)
> > +					return ret;
> > +			}
> > +		}
> > +
> > +		state.duty_cycle = 0;
> > +		state.enabled = false;
> > +		ret = pwm_apply_state(ctx->pwm, &state);
> > +	}
> > +
> > +	return ret;
> > 
> >  }
> > 
> > -static void pwm_fan_pwm_disable(void *__ctx)
> > +static void pwm_fan_cleanup(void *__ctx)
> > 
> >  {
> >  
> >  	struct pwm_fan_ctx *ctx = __ctx;
> > 
> > -
> > -	ctx->pwm_state.enabled = false;
> > -	pwm_apply_state(ctx->pwm, &ctx->pwm_state);
> > 
> >  	del_timer_sync(&ctx->rpm_timer);
> > 
> > +	__pwm_fan_disable_or_cleanup(ctx, true);
> > +}
> > +
> > +static int pwm_fan_disable(void *__ctx)
> > +{
> > +	struct pwm_fan_ctx *ctx = __ctx;
> > +
> > +	return __pwm_fan_disable_or_cleanup(ctx, false);
> > 
> >  }
> >  
> >  static int pwm_fan_probe(struct platform_device *pdev)
> > 
> > @@ -324,19 +388,14 @@ static int pwm_fan_probe(struct platform_device
> > *pdev)> 
> >  			return PTR_ERR(ctx->reg_en);
> >  		
> >  		ctx->reg_en = NULL;
> > 
> > -	} else {
> > -		ret = regulator_enable(ctx->reg_en);
> > -		if (ret) {
> > -			dev_err(dev, "Failed to enable fan supply: 
%d\n", ret);
> > -			return ret;
> > -		}
> > -		ret = devm_add_action_or_reset(dev, 
pwm_fan_regulator_disable,
> > -					       ctx->reg_en);
> > -		if (ret)
> > -			return ret;
> > 
> >  	}
> >  	
> >  	pwm_init_state(ctx->pwm, &ctx->pwm_state);
> > 
> > +	/*
> > +	 * Ensure the PWM is switched on (including the regulator),
> > +	 * independently from any previous PWM state
> > +	 */
> > +	ctx->pwm_state.enabled = false;
> > 
> >  	/*
> >  	
> >  	 * __set_pwm assumes that MAX_PWM * (period - 1) fits into an 
unsigned
> > 
> > @@ -348,14 +407,17 @@ static int pwm_fan_probe(struct platform_device
> > *pdev)> 
> >  		return -EINVAL;
> >  	
> >  	}
> > 
> > -	/* Set duty cycle to maximum allowed and enable PWM output */
> > +	/*
> > +	 * Set duty cycle to maximum allowed and enable PWM output as well 
as
> > +	 * the regulator. In case of error nothing is changed
> > +	 */
> > 
> >  	ret = __set_pwm(ctx, MAX_PWM);
> >  	if (ret) {
> >  	
> >  		dev_err(dev, "Failed to configure PWM: %d\n", ret);
> >  		return ret;
> >  	
> >  	}
> >  	timer_setup(&ctx->rpm_timer, sample_timer, 0);
> > 
> > -	ret = devm_add_action_or_reset(dev, pwm_fan_pwm_disable, ctx);
> > +	ret = devm_add_action_or_reset(dev, pwm_fan_cleanup, ctx);
> > 
> >  	if (ret)
> >  	
> >  		return ret;
> > 
> > @@ -461,42 +523,22 @@ static int pwm_fan_probe(struct platform_device
> > *pdev)> 
> >  	return 0;
> >  
> >  }
> > 
> > -static int pwm_fan_disable(struct device *dev)
> > -{
> > -	struct pwm_fan_ctx *ctx = dev_get_drvdata(dev);
> > -	int ret;
> > -
> > -	if (ctx->pwm_value) {
> > -		/* keep ctx->pwm_state unmodified for pwm_fan_resume() 
*/
> > -		struct pwm_state state = ctx->pwm_state;
> > -
> > -		state.duty_cycle = 0;
> > -		state.enabled = false;
> > -		ret = pwm_apply_state(ctx->pwm, &state);
> > -		if (ret < 0)
> > -			return ret;
> > -	}
> > -
> > -	if (ctx->reg_en) {
> > -		ret = regulator_disable(ctx->reg_en);
> > -		if (ret) {
> > -			dev_err(dev, "Failed to disable fan supply: 
%d\n", ret);
> > -			return ret;
> > -		}
> > -	}
> > -
> > -	return 0;
> > -}
> > -
> > 
> >  static void pwm_fan_shutdown(struct platform_device *pdev)
> >  {
> > 
> > -	pwm_fan_disable(&pdev->dev);
> > +	struct pwm_fan_ctx *ctx = platform_get_drvdata(pdev);
> > +
> > +	pwm_fan_cleanup(ctx);
> > 
> >  }
> >  
> >  #ifdef CONFIG_PM_SLEEP
> >  static int pwm_fan_suspend(struct device *dev)
> >  {
> > 
> > -	return pwm_fan_disable(dev);
> > +	struct pwm_fan_ctx *ctx = dev_get_drvdata(dev);
> > +	int ret;
> > +
> > +	ret = pwm_fan_disable(ctx);
> > +
> > +	return ret;
> > 
> >  }
> >  
> >  static int pwm_fan_resume(struct device *dev)
> > 
> > @@ -504,6 +546,9 @@ static int pwm_fan_resume(struct device *dev)
> > 
> >  	struct pwm_fan_ctx *ctx = dev_get_drvdata(dev);
> >  	int ret;
> > 
> > +	if (ctx->pwm_value == 0)
> > +		return 0;
> > +
> > 
> >  	if (ctx->reg_en) {
> >  	
> >  		ret = regulator_enable(ctx->reg_en);
> >  		if (ret) {
> > 
> > @@ -512,9 +557,6 @@ static int pwm_fan_resume(struct device *dev)
> > 
> >  		}
> >  	
> >  	}
> > 
> > -	if (ctx->pwm_value == 0)
> > -		return 0;
> > -
> > 
> >  	return pwm_apply_state(ctx->pwm, &ctx->pwm_state);
> >  
> >  }
> >  #endif