linux-kernel - Re: [PATCH] input: misc: pwm-vibra: Prevent unbalanced regulator

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Date:   Wed, 16 Jan 2019 23:08:38 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Paweł Chmiel <pawel.mikolaj.chmiel@...il.com>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jonathan Bakker <xc-racer2@...e.ca>
Subject: Re: [PATCH] input: misc: pwm-vibra: Prevent unbalanced regulator

Hi Paweł,

On Wed, Jan 16, 2019 at 10:11:31PM +0100, Paweł Chmiel wrote:
> From: Jonathan Bakker <xc-racer2@...e.ca>
> 
> pwm_vibrator_stop disables the regulator, but it can be called from
> multiple places, even when the regulator is already disabled. Fix this
> by using regulator_is_enabled check when starting and stopping device.
> 
> Signed-off-by: Jonathan Bakker <xc-racer2@...e.ca>
> Signed-off-by: Paweł Chmiel <pawel.mikolaj.chmiel@...il.com>
> ---
>  drivers/input/misc/pwm-vibra.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/input/misc/pwm-vibra.c b/drivers/input/misc/pwm-vibra.c
> index 55da191ae550..66677ee770ca 100644
> --- a/drivers/input/misc/pwm-vibra.c
> +++ b/drivers/input/misc/pwm-vibra.c
> @@ -42,10 +42,12 @@ static int pwm_vibrator_start(struct pwm_vibrator *vibrator)
>  	struct pwm_state state;
>  	int err;
>  
> -	err = regulator_enable(vibrator->vcc);
> -	if (err) {
> -		dev_err(pdev, "failed to enable regulator: %d", err);
> -		return err;
> +	if (!regulator_is_enabled(vibrator->vcc)) {

I do not think this is correct in case of shared supply, as this checks
global state of regulator. That means that if there is another user, we
may forego enabling regulator here, and that anther user may power it
down and vibrator will stop working.

I think you need a local flag here.

> +		err = regulator_enable(vibrator->vcc);
> +		if (err) {
> +			dev_err(pdev, "failed to enable regulator: %d", err);
> +			return err;
> +		}
>  	}
>  
>  	pwm_get_state(vibrator->pwm, &state);
> @@ -76,7 +78,8 @@ static int pwm_vibrator_start(struct pwm_vibrator *vibrator)
>  
>  static void pwm_vibrator_stop(struct pwm_vibrator *vibrator)
>  {
> -	regulator_disable(vibrator->vcc);
> +	if (regulator_is_enabled(vibrator->vcc))
> +		regulator_disable(vibrator->vcc);

Looking at this, I wonder if we should not disable PWMs first and the
disable regulator.

>  
>  	if (vibrator->pwm_dir)
>  		pwm_disable(vibrator->pwm_dir);
> -- 
> 2.17.1
> 

Thanks.

-- 
Dmitry