Re: [PATCH v2 3/3] Input: pwm-beeper: add optional amplifier regulator

[David Lechner]

On 01/14/2017 01:19 PM, Dmitry Torokhov wrote:
> On Wed, Jan 11, 2017 at 02:02:01PM -0600, David Lechner wrote:
> > This adds an optional regulator to the pwm-beeper device. This regulator
> > acts as an amplifier. The amplifier is only enabled while beeping in order
> > to reduce power consumption.
> >
> > Tested on LEGO MINDSTORMS EV3, which has a speaker connected to PWM through
> > an amplifier.
> >
> > Signed-off-by: David Lechner <david@xxxxxxxxxxxxxx>
> > ---
> >  drivers/input/misc/pwm-beeper.c | 29 ++++++++++++++++++++++++++++-
> >  1 file changed, 28 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/input/misc/pwm-beeper.c b/drivers/input/misc/pwm-beeper.c
> > index 30ac227..708e88e 100644
> > --- a/drivers/input/misc/pwm-beeper.c
> > +++ b/drivers/input/misc/pwm-beeper.c
> > @@ -14,6 +14,7 @@
> >   */
> >
> >  #include <linux/input.h>
> > +#include <linux/regulator/consumer.h>
> >  #include <linux/module.h>
> >  #include <linux/kernel.h>
> >  #include <linux/of.h>
> > @@ -25,8 +26,10 @@
> >  struct pwm_beeper {
> >  	struct input_dev *input;
> >  	struct pwm_device *pwm;
> > +	struct regulator *reg;
> >  	struct work_struct work;
> >  	unsigned long period;
> > +	bool reg_enabled;
> >  };
> >
> >  #define HZ_TO_NANOSECONDS(x) (1000000000UL/(x))
> > @@ -38,8 +41,20 @@ static void __pwm_beeper_set(struct pwm_beeper *beeper)
> >  	if (period) {
> >  		pwm_config(beeper->pwm, period / 2, period);
> >  		pwm_enable(beeper->pwm);
> > -	} else
> > +		if (beeper->reg) {
> > +			int error;
> > +
> > +			error = regulator_enable(beeper->reg);
> > +			if (!error)
> > +				beeper->reg_enabled = true;
> > +		}
> > +	} else {
> > +		if (beeper->reg_enabled) {
> > +			regulator_disable(beeper->reg);
> > +			beeper->reg_enabled = false;
> > +		}
> >  		pwm_disable(beeper->pwm);
> > +	}
> >  }
> >
> >  static void pwm_beeper_work(struct work_struct *work)
> > @@ -82,6 +97,10 @@ static void pwm_beeper_stop(struct pwm_beeper *beeper)
> >  {
> >  	cancel_work_sync(&beeper->work);
> >
> > +	if (beeper->reg_enabled) {
> > +		regulator_disable(beeper->reg);
> > +		beeper->reg_enabled = false;
> > +	}
> >  	if (beeper->period)
> >  		pwm_disable(beeper->pwm);
> >  }
> > @@ -111,6 +130,14 @@ static int pwm_beeper_probe(struct platform_device *pdev)
> >  		return error;
> >  	}
> >
> > +	beeper->reg = devm_regulator_get_optional(&pdev->dev, "amp");
>
> If you do not use optional regulator then you will not have to check if
> you have it or not everywhere: regulator core will give you a dummy that
> you can toggle to your heart's content.

Some months ago, I learned that if you are not using device tree and you 
do not call regulator_has_full_constraints(), then you do not get a 
dummy regulator. And here, we are only checking if the regulator exists 
in one place. We will still need the checks for beeper->reg_enabled to 
keep calls to regulator_enable() and regulator_disable() balanced.

On the other hand, it is recommended that you always call 
regulator_has_full_constraints(), so I don't mind changing it if that is 
what you think we should do. But, I don't really see much of an 
advantage to changing it compared to the current implementation.

> > +	error = PTR_ERR_OR_ZERO(beeper->reg);
> > +	if (error) {
> > +		if (error != -EPROBE_DEFER)
> > +			dev_err(dev, "Failed to get amp regulator\n");
> > +		return error;
> > +	}
> > +
> >  	/*
> >  	 * FIXME: pwm_apply_args() should be removed when switching to
> >  	 * the atomic PWM API.
> > --
> > 2.7.4
>
> Thanks.