Date:   Mon, 12 Apr 2021 18:18:08 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     linux-pwm@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Sven Van Asbroeck <TheSven73@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 1/8] pwm: pca9685: Switch to atomic API

Hello Clemens,

On Mon, Apr 12, 2021 at 03:27:38PM +0200, Clemens Gruber wrote:
> The switch to the atomic API goes hand in hand with a few fixes to
> previously experienced issues:
> - The duty cycle is no longer lost after disable/enable (previously the
>   OFF registers were cleared in disable and the user was required to
>   call config to restore the duty cycle settings)
> - If one sets a period resulting in the same prescale register value,
>   the sleep and write to the register is now skipped
> - Previously, only the full ON bit was toggled in GPIO mode (and full
>   OFF cleared if set to high), which could result in both full OFF and
>   full ON not being set and on=0, off=0, which is not allowed according
>   to the datasheet
> - The OFF registers were reset to 0 in probe, which could lead to the
>   forbidden on=0, off=0. Fixed by resetting to POR default (full OFF)
> 
> Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> ---
> Changes since v7:
> - Moved check for !state->enabled before prescaler configuration
> - Removed unnecessary cast
> - Use DIV_ROUND_DOWN in .apply
> 
> Changes since v6:
> - Order of a comparison switched for improved readability
> 
> Changes since v5:
> - Function documentation for set_duty
> - Variable initializations
> - Print warning if all LEDs channel
> - Changed EOPNOTSUPP to EINVAL
> - Improved error messages
> - Register reset corrections moved to this patch
> 
> Changes since v4:
> - Patches split up
> - Use a single set_duty function
> - Improve readability / new macros
> - Added a patch to restrict prescale changes to the first user
> 
> Changes since v3:
> - Refactoring: Extracted common functions
> - Read prescale register value instead of caching it
> - Return all zeros and disabled for "all LEDs" channel state
> - Improved duty calculation / mapping to 0..4096
> 
> Changes since v2:
> - Always set default prescale value in probe
> - Simplified probe code
> - Inlined functions with one callsite
> 
> Changes since v1:
> - Fixed a logic error
> - Impoved PM runtime handling and fixed !CONFIG_PM
> - Write default prescale reg value if invalid in probe
> - Reuse full_off/_on functions throughout driver
> - Use cached prescale value whenever possible
> 
>  drivers/pwm/pwm-pca9685.c | 259 +++++++++++++-------------------------
>  1 file changed, 89 insertions(+), 170 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 4a55dc18656c..827b57ced3c2 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -51,7 +51,6 @@
>  #define PCA9685_PRESCALE_MAX	0xFF	/* => min. frequency of 24 Hz */
>  
>  #define PCA9685_COUNTER_RANGE	4096
> -#define PCA9685_DEFAULT_PERIOD	5000000	/* Default period_ns = 1/200 Hz */
>  #define PCA9685_OSC_CLOCK_MHZ	25	/* Internal oscillator with 25 MHz */
>  
>  #define PCA9685_NUMREGS		0xFF
> @@ -71,10 +70,14 @@
>  #define LED_N_OFF_H(N)	(PCA9685_LEDX_OFF_H + (4 * (N)))
>  #define LED_N_OFF_L(N)	(PCA9685_LEDX_OFF_L + (4 * (N)))
>  
> +#define REG_ON_H(C)	((C) >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_ON_H : LED_N_ON_H((C)))
> +#define REG_ON_L(C)	((C) >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_ON_L : LED_N_ON_L((C)))
> +#define REG_OFF_H(C)	((C) >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_OFF_H : LED_N_OFF_H((C)))
> +#define REG_OFF_L(C)	((C) >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_OFF_L : LED_N_OFF_L((C)))

I'd like to see these named PCA9685_REG_ON_H etc.

>  struct pca9685 {
>  	struct pwm_chip chip;
>  	struct regmap *regmap;
> -	int period_ns;
>  #if IS_ENABLED(CONFIG_GPIOLIB)
>  	struct mutex lock;
>  	struct gpio_chip gpio;
> @@ -87,6 +90,51 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip)
>  	return container_of(chip, struct pca9685, chip);
>  }
>  
> +/* Helper function to set the duty cycle ratio to duty/4096 (e.g. duty=2048 -> 50%) */
> +static void pca9685_pwm_set_duty(struct pca9685 *pca, int channel, unsigned int duty)
> +{
> +	if (duty == 0) {
> +		/* Set the full OFF bit, which has the highest precedence */
> +		regmap_write(pca->regmap, REG_OFF_H(channel), LED_FULL);
> +	} else if (duty >= PCA9685_COUNTER_RANGE) {
> +		/* Set the full ON bit and clear the full OFF bit */
> +		regmap_write(pca->regmap, REG_ON_H(channel), LED_FULL);
> +		regmap_write(pca->regmap, REG_OFF_H(channel), 0);
> +	} else {
> +		/* Set OFF time (clears the full OFF bit) */
> +		regmap_write(pca->regmap, REG_OFF_L(channel), duty & 0xff);
> +		regmap_write(pca->regmap, REG_OFF_H(channel), (duty >> 8) & 0xf);
> +		/* Clear the full ON bit */
> +		regmap_write(pca->regmap, REG_ON_H(channel), 0);
> +	}
> +}
> +
> +static unsigned int pca9685_pwm_get_duty(struct pca9685 *pca, int channel)
> +{
> +	unsigned int off_h = 0, val = 0;
> +
> +	if (WARN_ON(channel >= PCA9685_MAXCHAN)) {
> +		/* HW does not support reading state of "all LEDs" channel */
> +		return 0;
> +	}
> +
> +	regmap_read(pca->regmap, LED_N_OFF_H(channel), &off_h);
> +	if (off_h & LED_FULL) {
> +		/* Full OFF bit is set */
> +		return 0;
> +	}
> +
> +	regmap_read(pca->regmap, LED_N_ON_H(channel), &val);
> +	if (val & LED_FULL) {
> +		/* Full ON bit is set */
> +		return PCA9685_COUNTER_RANGE;
> +	}
> +
> +	val = 0;
> +	regmap_read(pca->regmap, LED_N_OFF_L(channel), &val);

I asked in the last round why you initialize val. You answered "just to
have it set to 0 in case regmap_read fails / val was not set." I wonder
if

	ret = regmap_read(pca->regmap, LED_N_OFF_L(channel), &val);
	if (!ret)
		/* 
		val = 0

would be better then and also make the intention obvious.

> +	return ((off_h & 0xf) << 8) | (val & 0xff);
> +}
> +
>  #if IS_ENABLED(CONFIG_GPIOLIB)
>  static bool pca9685_pwm_test_and_set_inuse(struct pca9685 *pca, int pwm_idx)
>  {
> @@ -138,34 +186,23 @@ static int pca9685_pwm_gpio_request(struct gpio_chip *gpio, unsigned int offset)
>  static int pca9685_pwm_gpio_get(struct gpio_chip *gpio, unsigned int offset)
>  {
>  	struct pca9685 *pca = gpiochip_get_data(gpio);
> -	struct pwm_device *pwm = &pca->chip.pwms[offset];
> -	unsigned int value;
>  
> -	regmap_read(pca->regmap, LED_N_ON_H(pwm->hwpwm), &value);
> -
> -	return value & LED_FULL;
> +	return pca9685_pwm_get_duty(pca, offset) != 0;
>  }
>  
>  static void pca9685_pwm_gpio_set(struct gpio_chip *gpio, unsigned int offset,
>  				 int value)
>  {
>  	struct pca9685 *pca = gpiochip_get_data(gpio);
> -	struct pwm_device *pwm = &pca->chip.pwms[offset];
> -	unsigned int on = value ? LED_FULL : 0;
> -
> -	/* Clear both OFF registers */
> -	regmap_write(pca->regmap, LED_N_OFF_L(pwm->hwpwm), 0);
> -	regmap_write(pca->regmap, LED_N_OFF_H(pwm->hwpwm), 0);
>  
> -	/* Set the full ON bit */
> -	regmap_write(pca->regmap, LED_N_ON_H(pwm->hwpwm), on);
> +	pca9685_pwm_set_duty(pca, offset, value ? PCA9685_COUNTER_RANGE : 0);
>  }
>  
>  static void pca9685_pwm_gpio_free(struct gpio_chip *gpio, unsigned int offset)
>  {
>  	struct pca9685 *pca = gpiochip_get_data(gpio);
>  
> -	pca9685_pwm_gpio_set(gpio, offset, 0);
> +	pca9685_pwm_set_duty(pca, offset, 0);
>  	pm_runtime_put(pca->chip.dev);
>  	pca9685_pwm_clear_inuse(pca, offset);
>  }
> @@ -246,167 +283,52 @@ static void pca9685_set_sleep_mode(struct pca9685 *pca, bool enable)
>  	}
>  }
>  
> -static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> -			      int duty_ns, int period_ns)
> +static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			     const struct pwm_state *state)
>  {
>  	struct pca9685 *pca = to_pca(chip);
> -	unsigned long long duty;
> -	unsigned int reg;
> -	int prescale;
> -
> -	if (period_ns != pca->period_ns) {
> -		prescale = DIV_ROUND_CLOSEST(PCA9685_OSC_CLOCK_MHZ * period_ns,
> -					     PCA9685_COUNTER_RANGE * 1000) - 1;
> -
> -		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.
> -			 */
> -			/* Put chip into sleep mode */
> -			pca9685_set_sleep_mode(pca, true);
> -
> -			/* Change the chip-wide output frequency */
> -			regmap_write(pca->regmap, PCA9685_PRESCALE, prescale);
> -
> -			/* Wake the chip up */
> -			pca9685_set_sleep_mode(pca, false);
> -
> -			pca->period_ns = period_ns;
> -		} else {
> -			dev_err(chip->dev,
> -				"prescaler not set: period out of bounds!\n");
> -			return -EINVAL;
> -		}
> -	}
> +	unsigned long long duty, prescale;
> +	unsigned int val = 0;
>  
> -	if (duty_ns < 1) {
> -		if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -			reg = PCA9685_ALL_LED_OFF_H;
> -		else
> -			reg = LED_N_OFF_H(pwm->hwpwm);
> +	if (state->polarity != PWM_POLARITY_NORMAL)
> +		return -EINVAL;
>  
> -		regmap_write(pca->regmap, reg, LED_FULL);
> -
> -		return 0;
> +	prescale = DIV_ROUND_CLOSEST_ULL(PCA9685_OSC_CLOCK_MHZ * state->period,
> +					 PCA9685_COUNTER_RANGE * 1000) - 1;
> +	if (prescale < PCA9685_PRESCALE_MIN || prescale > PCA9685_PRESCALE_MAX) {
> +		dev_err(chip->dev, "pwm not changed: period out of bounds!\n");
> +		return -EINVAL;
>  	}
>  
> -	if (duty_ns == period_ns) {
> -		/* Clear both OFF registers */
> -		if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -			reg = PCA9685_ALL_LED_OFF_L;
> -		else
> -			reg = LED_N_OFF_L(pwm->hwpwm);
> -
> -		regmap_write(pca->regmap, reg, 0x0);
> -
> -		if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -			reg = PCA9685_ALL_LED_OFF_H;
> -		else
> -			reg = LED_N_OFF_H(pwm->hwpwm);
> -
> -		regmap_write(pca->regmap, reg, 0x0);
> -
> -		/* Set the full ON bit */
> -		if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -			reg = PCA9685_ALL_LED_ON_H;
> -		else
> -			reg = LED_N_ON_H(pwm->hwpwm);
> -
> -		regmap_write(pca->regmap, reg, LED_FULL);
> -
> +	if (!state->enabled) {
> +		pca9685_pwm_set_duty(pca, pwm->hwpwm, 0);
>  		return 0;
>  	}
>  
> -	duty = PCA9685_COUNTER_RANGE * (unsigned long long)duty_ns;
> -	duty = DIV_ROUND_UP_ULL(duty, period_ns);
> -
> -	if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -		reg = PCA9685_ALL_LED_OFF_L;
> -	else
> -		reg = LED_N_OFF_L(pwm->hwpwm);
> -
> -	regmap_write(pca->regmap, reg, (int)duty & 0xff);
> -
> -	if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -		reg = PCA9685_ALL_LED_OFF_H;
> -	else
> -		reg = LED_N_OFF_H(pwm->hwpwm);
> -
> -	regmap_write(pca->regmap, reg, ((int)duty >> 8) & 0xf);
> -
> -	/* Clear the full ON bit, otherwise the set OFF time has no effect */
> -	if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -		reg = PCA9685_ALL_LED_ON_H;
> -	else
> -		reg = LED_N_ON_H(pwm->hwpwm);
> -
> -	regmap_write(pca->regmap, reg, 0);
> -
> -	return 0;
> -}
> -
> -static int pca9685_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> -{
> -	struct pca9685 *pca = to_pca(chip);
> -	unsigned int reg;
> -
> -	/*
> -	 * The PWM subsystem does not support a pre-delay.
> -	 * So, set the ON-timeout to 0
> -	 */
> -	if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -		reg = PCA9685_ALL_LED_ON_L;
> -	else
> -		reg = LED_N_ON_L(pwm->hwpwm);
> -
> -	regmap_write(pca->regmap, reg, 0);
> -
> -	if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -		reg = PCA9685_ALL_LED_ON_H;
> -	else
> -		reg = LED_N_ON_H(pwm->hwpwm);
> -
> -	regmap_write(pca->regmap, reg, 0);
> +	regmap_read(pca->regmap, PCA9685_PRESCALE, &val);
> +	if (prescale != val) {
> +		/*
> +		 * 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.
> +		 */
> +		/* Put chip into sleep mode */
> +		pca9685_set_sleep_mode(pca, true);
>  
> -	/*
> -	 * Clear the full-off bit.
> -	 * It has precedence over the others and must be off.
> -	 */
> -	if (pwm->hwpwm >= PCA9685_MAXCHAN)
> -		reg = PCA9685_ALL_LED_OFF_H;
> -	else
> -		reg = LED_N_OFF_H(pwm->hwpwm);
> +		/* Change the chip-wide output frequency */
> +		regmap_write(pca->regmap, PCA9685_PRESCALE, prescale);
>  
> -	regmap_update_bits(pca->regmap, reg, LED_FULL, 0x0);
> +		/* Wake the chip up */
> +		pca9685_set_sleep_mode(pca, false);
> +	}
>  
> +	duty = PCA9685_COUNTER_RANGE * state->duty_cycle;
> +	duty = DIV_ROUND_DOWN_ULL(duty, state->period);

If you round down here you should probably also round down in the
calculation of prescale. Also note that you're losing precision by using
state->period.

Consider the following request: state->period = 4177921 [ns] +
state->duty_cycle = 100000 [ns], then we get
PRESCALE = round(25 * state->period / 4096000) - 1 = 25 and so an actual
period of 4096000 / 25 * (25 + 1) = 4259840 [ns]. If you now calculate
the duty using 4096 * 100000 / 4177920 = 98, this corresponds to an
actual duty cycle of 98 * 4259840 / 4096 = 101920 ns while you should
actually configure 96 to get 99840 ns.

So in the end I'd like to have the following:

	PRESCALE = round-down(25 * state->period / 4096000) - 1

(to get the biggest period not bigger than state->period) and

	duty = round-down(state->duty_cycle * 25 / ((PRESCALE + 1) * 1000))

(to get the biggest duty cycle not bigger than state->duty_cycle). With
the example above this yields

	PRESCALE = 24
	duty = 100

which results in

	.period = 4096000 / 25 * 25 = 4096000 [ns]
	.duty_cycle = 100000 [ns]
	
Now you have a mixture of old and new with no consistent behaviour. So
please either stick to the old behaviour or do it right immediately.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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