Re: [PATCH v8 6/8] pwm: pca9685: Support new PWM_USAGE_POWER flag

[Uwe Kleine-König]

On Mon, Apr 12, 2021 at 03:27:43PM +0200, Clemens Gruber wrote:
> If PWM_USAGE_POWER is set on a PWM, the pca9685 driver will phase shift
> the individual channels relative to their channel number. This improves
> EMI because the enabled channels no longer turn on at the same time,
> while still maintaining the configured duty cycle / power output.
> 
> Signed-off-by: Clemens Gruber <clemens.gruber@xxxxxxxxxxxx>
> ---
>  drivers/pwm/pwm-pca9685.c | 63 ++++++++++++++++++++++++++++++---------
>  1 file changed, 49 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 7f97965033e7..410b93b115dc 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -93,46 +93,76 @@ static inline struct pca9685 *to_pca(struct pwm_chip *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)
>  {
> +	struct pwm_device *pwm = &pca->chip.pwms[channel];
> +	unsigned int on, off;
> +
>  	if (duty == 0) {
>  		/* Set the full OFF bit, which has the highest precedence */
>  		regmap_write(pca->regmap, REG_OFF_H(channel), LED_FULL);
> +		return;
>  	} 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);
> +		return;
>  	}
> +
> +
> +	if (pwm->args.usage_power && channel < PCA9685_MAXCHAN) {
> +		/*
> +		 * If PWM_USAGE_POWER is set on a PWM, the pca9685
> +		 * driver will phase shift the individual channels
> +		 * relative to their channel number.
> +		 * This improves EMI because the enabled channels no
> +		 * longer turn on at the same time, while still
> +		 * maintaining the configured duty cycle / power output.
> +		 */
> +		on = channel * PCA9685_COUNTER_RANGE / PCA9685_MAXCHAN;
> +	} else
> +		on = 0;
> +
> +	off = (on + duty) % PCA9685_COUNTER_RANGE;
> +
> +	/* Set ON time (clears full ON bit) */
> +	regmap_write(pca->regmap, REG_ON_L(channel), on & 0xff);
> +	regmap_write(pca->regmap, REG_ON_H(channel), (on >> 8) & 0xf);
> +	/* Set OFF time (clears full OFF bit) */
> +	regmap_write(pca->regmap, REG_OFF_L(channel), off & 0xff);
> +	regmap_write(pca->regmap, REG_OFF_H(channel), (off >> 8) & 0xf);
>  }
>  
>  static unsigned int pca9685_pwm_get_duty(struct pca9685 *pca, int channel)
>  {
> -	unsigned int off_h = 0, val = 0;
> +	struct pwm_device *pwm = &pca->chip.pwms[channel];
> +	unsigned int off = 0, on = 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) {
> +	regmap_read(pca->regmap, LED_N_OFF_H(channel), &off);
> +	if (off & LED_FULL) {
>  		/* Full OFF bit is set */
>  		return 0;
>  	}
>  
> -	regmap_read(pca->regmap, LED_N_ON_H(channel), &val);
> -	if (val & LED_FULL) {
> +	regmap_read(pca->regmap, LED_N_ON_H(channel), &on);
> +	if (on & LED_FULL) {
>  		/* Full ON bit is set */
>  		return PCA9685_COUNTER_RANGE;
>  	}
>  
> -	val = 0;
>  	regmap_read(pca->regmap, LED_N_OFF_L(channel), &val);
> -	return ((off_h & 0xf) << 8) | (val & 0xff);
> +	off = ((off & 0xf) << 8) | (val & 0xff);
> +	if (!pwm->args.usage_power)
> +		return off;
> +
> +	/* Read ON register to calculate duty cycle of staggered output */
> +	val = 0;
> +	regmap_read(pca->regmap, LED_N_ON_L(channel), &val);
> +	on = ((on & 0xf) << 8) | (val & 0xff);
> +	return (off - on) & (PCA9685_COUNTER_RANGE - 1);

If LED_N_ON is != 0 but usage_power is false, the returned state is
bogus.

>  }
>  
>  #if IS_ENABLED(CONFIG_GPIOLIB)
> @@ -439,9 +469,11 @@ static int pca9685_pwm_probe(struct i2c_client *client,
>  	reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
>  	regmap_write(pca->regmap, PCA9685_MODE1, reg);
>  
> -	/* Reset OFF registers to POR default */
> +	/* Reset OFF/ON registers to POR default */
>  	regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, LED_FULL);
>  	regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
> +	regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> +	regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
>  
>  	pca->chip.ops = &pca9685_pwm_ops;
>  	/* Add an extra channel for ALL_LED */
> @@ -450,6 +482,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
>  	pca->chip.dev = &client->dev;
>  	pca->chip.base = -1;
>  
> +	pca->chip.of_xlate = of_pwm_xlate_with_flags;
> +	pca->chip.of_pwm_n_cells = 3;
> +

Huh, you're incompatibly changing the device tree binding here.

Best regards
Uwe

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

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