[v3,3/4] pwm: pca9685: Support staggered output ON times
diff mbox series

Message ID 20201124181013.162176-3-clemens.gruber@pqgruber.com
State New, archived
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Series
  • [v3,1/4] pwm: pca9685: Switch to atomic API
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Commit Message

Clemens Gruber Nov. 24, 2020, 6:10 p.m. UTC
The PCA9685 supports staggered LED output ON times to minimize current
surges and reduce EMI.
When this new option is enabled, the ON times of each channel are
delayed by channel number x counter range / 16, which avoids asserting
all enabled outputs at the same counter value while still maintaining
the configured duty cycle of each output.

Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
---

Changes since v1:
- Rebased

 drivers/pwm/pwm-pca9685.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

Comments

Sven Van Asbroeck Nov. 25, 2020, 3:51 a.m. UTC | #1
On Tue, Nov 24, 2020 at 1:10 PM Clemens Gruber
<clemens.gruber@pqgruber.com> wrote:
>
> The PCA9685 supports staggered LED output ON times to minimize current
> surges and reduce EMI.
> When this new option is enabled, the ON times of each channel are
> delayed by channel number x counter range / 16, which avoids asserting
> all enabled outputs at the same counter value while still maintaining
> the configured duty cycle of each output.
>
> Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
> ---
>
> Changes since v1:
> - Rebased
>
>  drivers/pwm/pwm-pca9685.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 2b82b35ff0de..37c80bc8edcf 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -75,6 +75,7 @@ struct pca9685 {
>         struct pwm_chip chip;
>         struct regmap *regmap;
>         int prescale;
> +       bool staggered_outputs;
>  #if IS_ENABLED(CONFIG_GPIOLIB)
>         struct mutex lock;
>         struct gpio_chip gpio;
> @@ -329,7 +330,7 @@ static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  {
>         struct pca9685 *pca = to_pca(chip);
>         unsigned long long duty, prescale;
> -       unsigned int reg;
> +       unsigned int on, off, reg;
>
>         if (state->polarity != PWM_POLARITY_NORMAL)
>                 return -EOPNOTSUPP;
> @@ -375,6 +376,32 @@ static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>         duty = (PCA9685_COUNTER_RANGE - 1) * state->duty_cycle;
>         duty = DIV_ROUND_UP_ULL(duty, state->period);
>
> +       if (pca->staggered_outputs) {
> +               if (pwm->hwpwm < PCA9685_MAXCHAN) {
> +                       /*
> +                        * To reduce EMI, the ON times of each channel are
> +                        * spread out evenly within the counter range, while
> +                        * still maintaining the configured duty cycle
> +                        */
> +                       on = pwm->hwpwm * PCA9685_COUNTER_RANGE /
> +                               PCA9685_MAXCHAN;
> +                       off = (on + duty) % PCA9685_COUNTER_RANGE;

Will pwm_get_state() still return the correct duty cycle in case
of staggered outputs?

> +                       regmap_write(pca->regmap, LED_N_ON_L(pwm->hwpwm),
> +                                    on & 0xff);
> +                       regmap_write(pca->regmap, LED_N_ON_H(pwm->hwpwm),
> +                                    (on >> 8) & 0xf);
> +                       regmap_write(pca->regmap, LED_N_OFF_L(pwm->hwpwm),
> +                                    off & 0xff);
> +                       regmap_write(pca->regmap, LED_N_OFF_H(pwm->hwpwm),
> +                                    (off >> 8) & 0xf);
> +                       return 0;
> +               }
> +
> +               /* No staggering possible if "all LEDs" channel is used */
> +               regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> +               regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
> +       }
> +
>         if (pwm->hwpwm >= PCA9685_MAXCHAN)
>                 reg = PCA9685_ALL_LED_OFF_L;
>         else
> @@ -470,6 +497,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
>
>         regmap_write(pca->regmap, PCA9685_MODE2, reg);
>
> +       pca->staggered_outputs = device_property_read_bool(
> +               &client->dev, "staggered-outputs");
> +
>         /* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions */
>         regmap_read(pca->regmap, PCA9685_MODE1, &reg);
>         reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
> @@ -478,6 +508,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
>         /* Reset OFF registers to HW default (only full OFF bit is set) */
>         regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);
>         regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
> +       /* Reset ON registers to HW default */
> +       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 */
> --
> 2.29.2
>
Clemens Gruber Nov. 25, 2020, 8:40 a.m. UTC | #2
On Tue, Nov 24, 2020 at 10:51:23PM -0500, Sven Van Asbroeck wrote:
> On Tue, Nov 24, 2020 at 1:10 PM Clemens Gruber
> <clemens.gruber@pqgruber.com> wrote:
> >
> > The PCA9685 supports staggered LED output ON times to minimize current
> > surges and reduce EMI.
> > When this new option is enabled, the ON times of each channel are
> > delayed by channel number x counter range / 16, which avoids asserting
> > all enabled outputs at the same counter value while still maintaining
> > the configured duty cycle of each output.
> >
> > Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
> > ---
> >
> > Changes since v1:
> > - Rebased
> >
> >  drivers/pwm/pwm-pca9685.c | 35 ++++++++++++++++++++++++++++++++++-
> >  1 file changed, 34 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> > index 2b82b35ff0de..37c80bc8edcf 100644
> > --- a/drivers/pwm/pwm-pca9685.c
> > +++ b/drivers/pwm/pwm-pca9685.c
> > @@ -75,6 +75,7 @@ struct pca9685 {
> >         struct pwm_chip chip;
> >         struct regmap *regmap;
> >         int prescale;
> > +       bool staggered_outputs;
> >  #if IS_ENABLED(CONFIG_GPIOLIB)
> >         struct mutex lock;
> >         struct gpio_chip gpio;
> > @@ -329,7 +330,7 @@ static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >  {
> >         struct pca9685 *pca = to_pca(chip);
> >         unsigned long long duty, prescale;
> > -       unsigned int reg;
> > +       unsigned int on, off, reg;
> >
> >         if (state->polarity != PWM_POLARITY_NORMAL)
> >                 return -EOPNOTSUPP;
> > @@ -375,6 +376,32 @@ static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >         duty = (PCA9685_COUNTER_RANGE - 1) * state->duty_cycle;
> >         duty = DIV_ROUND_UP_ULL(duty, state->period);
> >
> > +       if (pca->staggered_outputs) {
> > +               if (pwm->hwpwm < PCA9685_MAXCHAN) {
> > +                       /*
> > +                        * To reduce EMI, the ON times of each channel are
> > +                        * spread out evenly within the counter range, while
> > +                        * still maintaining the configured duty cycle
> > +                        */
> > +                       on = pwm->hwpwm * PCA9685_COUNTER_RANGE /
> > +                               PCA9685_MAXCHAN;
> > +                       off = (on + duty) % PCA9685_COUNTER_RANGE;
> 
> Will pwm_get_state() still return the correct duty cycle in case
> of staggered outputs?

No, but it should. I will improve the get_state function in the next
version to cover all cases.

Thanks for your input. This would have been a mess without your feedback
;)

> 
> > +                       regmap_write(pca->regmap, LED_N_ON_L(pwm->hwpwm),
> > +                                    on & 0xff);
> > +                       regmap_write(pca->regmap, LED_N_ON_H(pwm->hwpwm),
> > +                                    (on >> 8) & 0xf);
> > +                       regmap_write(pca->regmap, LED_N_OFF_L(pwm->hwpwm),
> > +                                    off & 0xff);
> > +                       regmap_write(pca->regmap, LED_N_OFF_H(pwm->hwpwm),
> > +                                    (off >> 8) & 0xf);
> > +                       return 0;
> > +               }
> > +
> > +               /* No staggering possible if "all LEDs" channel is used */
> > +               regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> > +               regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
> > +       }
> > +
> >         if (pwm->hwpwm >= PCA9685_MAXCHAN)
> >                 reg = PCA9685_ALL_LED_OFF_L;
> >         else
> > @@ -470,6 +497,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> >
> >         regmap_write(pca->regmap, PCA9685_MODE2, reg);
> >
> > +       pca->staggered_outputs = device_property_read_bool(
> > +               &client->dev, "staggered-outputs");
> > +
> >         /* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions */
> >         regmap_read(pca->regmap, PCA9685_MODE1, &reg);
> >         reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
> > @@ -478,6 +508,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> >         /* Reset OFF registers to HW default (only full OFF bit is set) */
> >         regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);
> >         regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
> > +       /* Reset ON registers to HW default */
> > +       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 */
> > --
> > 2.29.2
> >

Patch
diff mbox series

diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
index 2b82b35ff0de..37c80bc8edcf 100644
--- a/drivers/pwm/pwm-pca9685.c
+++ b/drivers/pwm/pwm-pca9685.c
@@ -75,6 +75,7 @@  struct pca9685 {
 	struct pwm_chip chip;
 	struct regmap *regmap;
 	int prescale;
+	bool staggered_outputs;
 #if IS_ENABLED(CONFIG_GPIOLIB)
 	struct mutex lock;
 	struct gpio_chip gpio;
@@ -329,7 +330,7 @@  static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 {
 	struct pca9685 *pca = to_pca(chip);
 	unsigned long long duty, prescale;
-	unsigned int reg;
+	unsigned int on, off, reg;
 
 	if (state->polarity != PWM_POLARITY_NORMAL)
 		return -EOPNOTSUPP;
@@ -375,6 +376,32 @@  static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	duty = (PCA9685_COUNTER_RANGE - 1) * state->duty_cycle;
 	duty = DIV_ROUND_UP_ULL(duty, state->period);
 
+	if (pca->staggered_outputs) {
+		if (pwm->hwpwm < PCA9685_MAXCHAN) {
+			/*
+			 * To reduce EMI, the ON times of each channel are
+			 * spread out evenly within the counter range, while
+			 * still maintaining the configured duty cycle
+			 */
+			on = pwm->hwpwm * PCA9685_COUNTER_RANGE /
+				PCA9685_MAXCHAN;
+			off = (on + duty) % PCA9685_COUNTER_RANGE;
+			regmap_write(pca->regmap, LED_N_ON_L(pwm->hwpwm),
+				     on & 0xff);
+			regmap_write(pca->regmap, LED_N_ON_H(pwm->hwpwm),
+				     (on >> 8) & 0xf);
+			regmap_write(pca->regmap, LED_N_OFF_L(pwm->hwpwm),
+				     off & 0xff);
+			regmap_write(pca->regmap, LED_N_OFF_H(pwm->hwpwm),
+				     (off >> 8) & 0xf);
+			return 0;
+		}
+
+		/* No staggering possible if "all LEDs" channel is used */
+		regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
+		regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
+	}
+
 	if (pwm->hwpwm >= PCA9685_MAXCHAN)
 		reg = PCA9685_ALL_LED_OFF_L;
 	else
@@ -470,6 +497,9 @@  static int pca9685_pwm_probe(struct i2c_client *client,
 
 	regmap_write(pca->regmap, PCA9685_MODE2, reg);
 
+	pca->staggered_outputs = device_property_read_bool(
+		&client->dev, "staggered-outputs");
+
 	/* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions */
 	regmap_read(pca->regmap, PCA9685_MODE1, &reg);
 	reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
@@ -478,6 +508,9 @@  static int pca9685_pwm_probe(struct i2c_client *client,
 	/* Reset OFF registers to HW default (only full OFF bit is set) */
 	regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);
 	regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
+	/* Reset ON registers to HW default */
+	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 */