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

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Message-ID: <a907970d-3ab9-69df-9636-54c2b660cff9@lechnology.com>
Date:   Sun, 15 Jan 2017 18:12:29 -0600
From:   David Lechner <david@...hnology.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] Input: pwm-beeper: add optional amplifier
 regulator

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@...hnology.com>
>> ---
>>  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.
>