Date:   Wed, 12 Apr 2017 11:53:50 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     thierry.reding@...il.com, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org, clemens.gruber@...ruber.com,
        andriy.shevchenko@...ux.intel.com,
        Sven Van Asbroeck <TheSven73@...glemail.com>
Subject: Re: [PATCH v2 1/1] pwm: pca9685: fix gpio-only operation.

On Tue, Apr 11, 2017 at 03:19:05PM -0400, Sven Van Asbroeck wrote:
> gpio-only driver operation never clears the SLEEP bit, which can
> cause the gpios to become unusable.
> 
> Example:
> 1. user requests first pwm  ->      driver clears SLEEP bit
> 2. user frees last pwm      ->      driver sets SLEEP bit
> 3. user requests gpio
> 4. user switches gpio on    ->      output does not turn on
>                                     because SLEEP bit is set
> 
> Prevent this behaviour by letting the runtime_pm framework
> control the SLEEP bit. This will put the chip to SLEEP if
> no pwms/gpios are exported/in use.

Looks like going to the right direction. I have a couple of comments see
below.

> 
> Fixes: bccec89f0a35 ("Allow any of the 16 PWMs to be used as a GPIO")
> Reported-by: Sven Van Asbroeck <TheSven73@...glemail.com>
> Signed-off-by: Sven Van Asbroeck <TheSven73@...glemail.com>
> Suggested-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ---
>  drivers/pwm/pwm-pca9685.c | 111 ++++++++++++++++++++++++++++++++--------------
>  1 file changed, 78 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 0cfb357..465eb57 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -30,6 +30,7 @@
>  #include <linux/regmap.h>
>  #include <linux/slab.h>
>  #include <linux/delay.h>
> +#include <linux/pm_runtime.h>
>  
>  /*
>   * Because the PCA9685 has only one prescaler per chip, changing the period of
> @@ -79,7 +80,6 @@
>  struct pca9685 {
>  	struct pwm_chip chip;
>  	struct regmap *regmap;
> -	int active_cnt;
>  	int duty_ns;
>  	int period_ns;
>  #if IS_ENABLED(CONFIG_GPIOLIB)
> @@ -111,20 +111,10 @@ static int pca9685_pwm_gpio_request(struct gpio_chip *gpio, unsigned int offset)
>  	pwm_set_chip_data(pwm, (void *)1);
>  
>  	mutex_unlock(&pca->lock);
> +	pm_runtime_get_sync(pca->chip.dev);
>  	return 0;
>  }
>  
> -static void pca9685_pwm_gpio_free(struct gpio_chip *gpio, unsigned int offset)
> -{
> -	struct pca9685 *pca = gpiochip_get_data(gpio);
> -	struct pwm_device *pwm;
> -
> -	mutex_lock(&pca->lock);
> -	pwm = &pca->chip.pwms[offset];
> -	pwm_set_chip_data(pwm, NULL);
> -	mutex_unlock(&pca->lock);
> -}
> -
>  static bool pca9685_pwm_is_gpio(struct pca9685 *pca, struct pwm_device *pwm)
>  {
>  	bool is_gpio = false;
> @@ -177,6 +167,19 @@ static void pca9685_pwm_gpio_set(struct gpio_chip *gpio, unsigned int offset,
>  	regmap_write(pca->regmap, LED_N_ON_H(pwm->hwpwm), on);
>  }
>  
> +static void pca9685_pwm_gpio_free(struct gpio_chip *gpio, unsigned int offset)
> +{
> +	struct pca9685 *pca = gpiochip_get_data(gpio);
> +	struct pwm_device *pwm;
> +
> +	pca9685_pwm_gpio_set(gpio, offset, 0);
> +	pm_runtime_put(pca->chip.dev);
> +	mutex_lock(&pca->lock);
> +	pwm = &pca->chip.pwms[offset];
> +	pwm_set_chip_data(pwm, NULL);
> +	mutex_unlock(&pca->lock);
> +}

Why did you move the function here?

> +
>  static int pca9685_pwm_gpio_get_direction(struct gpio_chip *chip,
>  					  unsigned int offset)
>  {
> @@ -238,6 +241,16 @@ static inline int pca9685_pwm_gpio_probe(struct pca9685 *pca)
>  }
>  #endif
>  
> +static void pca9685_set_sleep_mode(struct pca9685 *pca, int sleep)
> +{
> +	regmap_update_bits(pca->regmap, PCA9685_MODE1,
> +			   MODE1_SLEEP, sleep ? MODE1_SLEEP : 0);
> +	if (!sleep) {
> +		/* Wait 500us for the oscillator to be back up */
> +		udelay(500);
> +	}
> +}
> +
>  static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  			      int duty_ns, int period_ns)
>  {
> @@ -252,19 +265,19 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  
>  		if (prescale >= PCA9685_PRESCALE_MIN &&
>  			prescale <= PCA9685_PRESCALE_MAX) {
> +			/* putting the chip briefly into SLEEP mode
> +			 * at this point won't interfere with the
> +			 * pm_runtime framework, because the pm_runtime
> +			 * state is guaranteed active here.
> +			 */

The comment style should follow the one in
Documentation/process/coding-style.rst.

>  			/* Put chip into sleep mode */
> -			regmap_update_bits(pca->regmap, PCA9685_MODE1,
> -					   MODE1_SLEEP, MODE1_SLEEP);
> +			pca9685_set_sleep_mode(pca, 1);
>  
>  			/* Change the chip-wide output frequency */
>  			regmap_write(pca->regmap, PCA9685_PRESCALE, prescale);
>  
>  			/* Wake the chip up */
> -			regmap_update_bits(pca->regmap, PCA9685_MODE1,
> -					   MODE1_SLEEP, 0x0);
> -
> -			/* Wait 500us for the oscillator to be back up */
> -			udelay(500);
> +			pca9685_set_sleep_mode(pca, 0);
>  
>  			pca->period_ns = period_ns;
>  		} else {
> @@ -406,21 +419,15 @@ static int pca9685_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
>  
>  	if (pca9685_pwm_is_gpio(pca, pwm))
>  		return -EBUSY;
> -
> -	if (pca->active_cnt++ == 0)
> -		return regmap_update_bits(pca->regmap, PCA9685_MODE1,
> -					  MODE1_SLEEP, 0x0);
> +	pm_runtime_get_sync(chip->dev);
>  
>  	return 0;
>  }
>  
>  static void pca9685_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
>  {
> -	struct pca9685 *pca = to_pca(chip);
> -
> -	if (--pca->active_cnt == 0)
> -		regmap_update_bits(pca->regmap, PCA9685_MODE1, MODE1_SLEEP,
> -				   MODE1_SLEEP);
> +	pca9685_pwm_disable(chip, pwm);
> +	pm_runtime_put(chip->dev);
>  }
>  
>  static const struct pwm_ops pca9685_pwm_ops = {
> @@ -492,21 +499,53 @@ static int pca9685_pwm_probe(struct i2c_client *client,
>  		return ret;
>  
>  	ret = pca9685_pwm_gpio_probe(pca);
> -	if (ret < 0)
> +	if (ret < 0) {
>  		pwmchip_remove(&pca->chip);
> +		return ret;
> +	}
>  
> -	return ret;
> +	/* the chip comes out of power-up in the active state */
> +	pm_runtime_set_active(&client->dev);
> +	/* enable will put the chip into suspend, which is what we
> +	 * want as all outputs are disabled at this point
> +	 */
> +	pm_runtime_enable(&client->dev);
> +
> +	return 0;
>  }
>  
>  static int pca9685_pwm_remove(struct i2c_client *client)
>  {
>  	struct pca9685 *pca = i2c_get_clientdata(client);
> +	int ret;
> +
> +	ret = pwmchip_remove(&pca->chip);
> +	if (ret)
> +		return ret;
> +	pm_runtime_suspend(&client->dev);

Is it necessary to call this? 

In principle you need to undo whatever you did in ->probe() so calling
pm_runtime_set_suspended() here makes more sense IMHO.

You can try how it works if you load/unload the driver several times-.

> +	pm_runtime_disable(&client->dev);
> +	return 0;
> +}
> +
> +#ifdef CONFIG_PM
> +static int pca9685_pwm_runtime_suspend(struct device *dev)
> +{
> +	struct i2c_client *client = to_i2c_client(dev);
> +	struct pca9685 *pca = i2c_get_clientdata(client);
>  
> -	regmap_update_bits(pca->regmap, PCA9685_MODE1, MODE1_SLEEP,
> -			   MODE1_SLEEP);
> +	pca9685_set_sleep_mode(pca, 1);
> +	return 0;
> +}
>  
> -	return pwmchip_remove(&pca->chip);
> +static int pca9685_pwm_runtime_resume(struct device *dev)
> +{
> +	struct i2c_client *client = to_i2c_client(dev);
> +	struct pca9685 *pca = i2c_get_clientdata(client);
> +
> +	pca9685_set_sleep_mode(pca, 0);
> +	return 0;
>  }
> +#endif
>  
>  static const struct i2c_device_id pca9685_id[] = {
>  	{ "pca9685", 0 },
> @@ -530,11 +569,17 @@ static int pca9685_pwm_remove(struct i2c_client *client)
>  MODULE_DEVICE_TABLE(of, pca9685_dt_ids);
>  #endif
>  
> +static const struct dev_pm_ops pca9685_pwm_pm = {
> +	SET_RUNTIME_PM_OPS(pca9685_pwm_runtime_suspend,
> +			   pca9685_pwm_runtime_resume, NULL)
> +};
> +
>  static struct i2c_driver pca9685_i2c_driver = {
>  	.driver = {
>  		.name = "pca9685-pwm",
>  		.acpi_match_table = ACPI_PTR(pca9685_acpi_ids),
>  		.of_match_table = of_match_ptr(pca9685_dt_ids),
> +		.pm = &pca9685_pwm_pm,
>  	},
>  	.probe = pca9685_pwm_probe,
>  	.remove = pca9685_pwm_remove,
> -- 
> 1.9.1

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