Message ID | 20201215212228.185517-5-clemens.gruber@pqgruber.com |
---|---|
State | Changes Requested |
Headers | show |
Series | [v5,1/7] pwm: pca9685: Switch to atomic API | expand |
Hi Clemens, see below. On Wed, Dec 16, 2020 at 7:53 AM 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> > --- > drivers/pwm/pwm-pca9685.c | 62 +++++++++++++++++++++++++++++++-------- > 1 file changed, 50 insertions(+), 12 deletions(-) > > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c > index 38aadaf50996..ff916980de49 100644 > --- a/drivers/pwm/pwm-pca9685.c > +++ b/drivers/pwm/pwm-pca9685.c > @@ -79,6 +79,7 @@ > struct pca9685 { > struct pwm_chip chip; > struct regmap *regmap; > + bool staggered_outputs; > #if IS_ENABLED(CONFIG_GPIOLIB) > struct mutex lock; > struct gpio_chip gpio; > @@ -93,45 +94,79 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip) > > static void pca9685_pwm_set_duty(struct pca9685 *pca, int channel, unsigned int duty) > { > + 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 (pca->staggered_outputs) { > + if (channel < 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 = channel * PCA9685_COUNTER_RANGE / PCA9685_MAXCHAN; > + off = (on + duty) % PCA9685_COUNTER_RANGE; > + regmap_write(pca->regmap, REG_ON_L(channel), on & 0xff); > + regmap_write(pca->regmap, REG_ON_H(channel), (on >> 8) & 0xf); > + regmap_write(pca->regmap, REG_OFF_L(channel), off & 0xff); > + regmap_write(pca->regmap, REG_OFF_H(channel), (off >> 8) & 0xf); > + return; > + } > + /* No staggering possible if "all LEDs" channel is used */ > + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0); > } > + /* 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); > } I find the set_duty() function quite hard to follow. Can we simplify this by eliminating the !staggered_outputs special case? E.g. always calculate and write 'on' and 'off'. But if !staggered_outputs => on = 0 and off = duty. Yes this adds one extra/unnecessary register write in the !staggered case, but simplicity/maintainability >>> efficiency here. And this "issue" will disappear when we switch on regmap caching. > > static unsigned int pca9685_pwm_get_duty(struct pca9685 *pca, int channel) > { > - unsigned int off_h, val; > + unsigned int off, on, val; > > if (WARN_ON(channel >= PCA9685_MAXCHAN)) { > /* Hardware readout not supported for "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; > } > > regmap_read(pca->regmap, LED_N_OFF_L(channel), &val); > - return ((off_h & 0xf) << 8) | (val & 0xff); > + off = ((off & 0xf) << 8) | (val & 0xff); > + > + if (pca->staggered_outputs) { > + regmap_read(pca->regmap, LED_N_ON_L(channel), &val); > + on = ((on & 0xf) << 8) | (val & 0xff); > + > + if (off >= on) > + return off - on; > + else > + return off + PCA9685_COUNTER_RANGE - on; I think the if/else is unnecessary. unsigned int is twos-complement, so we can just write: return (off - on) & 0xfff; (or PCA9685_COUNTER_RANGE - 1) and it will "magically" work even if off < on. > + } > + > + return off; > } As in set_duty(), consider removing the !staggered_outputs special case, to make this function clearer and simpler. > > #if IS_ENABLED(CONFIG_GPIOLIB) > @@ -442,6 +477,9 @@ 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, "nxp,staggered-outputs"); > + > /* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions */ > regmap_read(pca->regmap, PCA9685_MODE1, ®); > reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3); > -- > 2.29.2 >
On Wed, Dec 16, 2020 at 11:02:57PM -0500, Sven Van Asbroeck wrote: > Hi Clemens, see below. > > On Wed, Dec 16, 2020 at 7:53 AM 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> > > --- > > drivers/pwm/pwm-pca9685.c | 62 +++++++++++++++++++++++++++++++-------- > > 1 file changed, 50 insertions(+), 12 deletions(-) > > > > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c > > index 38aadaf50996..ff916980de49 100644 > > --- a/drivers/pwm/pwm-pca9685.c > > +++ b/drivers/pwm/pwm-pca9685.c > > @@ -79,6 +79,7 @@ > > struct pca9685 { > > struct pwm_chip chip; > > struct regmap *regmap; > > + bool staggered_outputs; > > #if IS_ENABLED(CONFIG_GPIOLIB) > > struct mutex lock; > > struct gpio_chip gpio; > > @@ -93,45 +94,79 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip) > > > > static void pca9685_pwm_set_duty(struct pca9685 *pca, int channel, unsigned int duty) > > { > > + 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 (pca->staggered_outputs) { > > + if (channel < 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 = channel * PCA9685_COUNTER_RANGE / PCA9685_MAXCHAN; > > + off = (on + duty) % PCA9685_COUNTER_RANGE; > > + regmap_write(pca->regmap, REG_ON_L(channel), on & 0xff); > > + regmap_write(pca->regmap, REG_ON_H(channel), (on >> 8) & 0xf); > > + regmap_write(pca->regmap, REG_OFF_L(channel), off & 0xff); > > + regmap_write(pca->regmap, REG_OFF_H(channel), (off >> 8) & 0xf); > > + return; > > + } > > + /* No staggering possible if "all LEDs" channel is used */ > > + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0); > > } > > + /* 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); > > } > > I find the set_duty() function quite hard to follow. > Can we simplify this by eliminating the !staggered_outputs special case? > E.g. always calculate and write 'on' and 'off'. > But if !staggered_outputs => on = 0 and off = duty. > > Yes this adds one extra/unnecessary register write in the !staggered case, > but simplicity/maintainability >>> efficiency here. And this "issue" will > disappear when we switch on regmap caching. No objections, I will eliminate the special case. > > > > > static unsigned int pca9685_pwm_get_duty(struct pca9685 *pca, int channel) > > { > > - unsigned int off_h, val; > > + unsigned int off, on, val; > > > > if (WARN_ON(channel >= PCA9685_MAXCHAN)) { > > /* Hardware readout not supported for "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; > > } > > > > regmap_read(pca->regmap, LED_N_OFF_L(channel), &val); > > - return ((off_h & 0xf) << 8) | (val & 0xff); > > + off = ((off & 0xf) << 8) | (val & 0xff); > > + > > + if (pca->staggered_outputs) { > > + regmap_read(pca->regmap, LED_N_ON_L(channel), &val); > > + on = ((on & 0xf) << 8) | (val & 0xff); > > + > > + if (off >= on) > > + return off - on; > > + else > > + return off + PCA9685_COUNTER_RANGE - on; > > I think the if/else is unnecessary. unsigned int is twos-complement, > so we can just write: > > return (off - on) & 0xfff; (or PCA9685_COUNTER_RANGE - 1) > > and it will "magically" work even if off < on. Ah, yes of course. Good catch! > > > > + } > > + > > + return off; > > } > > As in set_duty(), consider removing the !staggered_outputs special case, > to make this function clearer and simpler. Yes, thanks. > > > > > #if IS_ENABLED(CONFIG_GPIOLIB) > > @@ -442,6 +477,9 @@ 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, "nxp,staggered-outputs"); > > + > > /* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions */ > > regmap_read(pca->regmap, PCA9685_MODE1, ®); > > reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3); > > -- > > 2.29.2 > >
diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c index 38aadaf50996..ff916980de49 100644 --- a/drivers/pwm/pwm-pca9685.c +++ b/drivers/pwm/pwm-pca9685.c @@ -79,6 +79,7 @@ struct pca9685 { struct pwm_chip chip; struct regmap *regmap; + bool staggered_outputs; #if IS_ENABLED(CONFIG_GPIOLIB) struct mutex lock; struct gpio_chip gpio; @@ -93,45 +94,79 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip) static void pca9685_pwm_set_duty(struct pca9685 *pca, int channel, unsigned int duty) { + 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 (pca->staggered_outputs) { + if (channel < 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 = channel * PCA9685_COUNTER_RANGE / PCA9685_MAXCHAN; + off = (on + duty) % PCA9685_COUNTER_RANGE; + regmap_write(pca->regmap, REG_ON_L(channel), on & 0xff); + regmap_write(pca->regmap, REG_ON_H(channel), (on >> 8) & 0xf); + regmap_write(pca->regmap, REG_OFF_L(channel), off & 0xff); + regmap_write(pca->regmap, REG_OFF_H(channel), (off >> 8) & 0xf); + return; + } + /* No staggering possible if "all LEDs" channel is used */ + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0); } + /* 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, val; + unsigned int off, on, val; if (WARN_ON(channel >= PCA9685_MAXCHAN)) { /* Hardware readout not supported for "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; } regmap_read(pca->regmap, LED_N_OFF_L(channel), &val); - return ((off_h & 0xf) << 8) | (val & 0xff); + off = ((off & 0xf) << 8) | (val & 0xff); + + if (pca->staggered_outputs) { + regmap_read(pca->regmap, LED_N_ON_L(channel), &val); + on = ((on & 0xf) << 8) | (val & 0xff); + + if (off >= on) + return off - on; + else + return off + PCA9685_COUNTER_RANGE - on; + } + + return off; } #if IS_ENABLED(CONFIG_GPIOLIB) @@ -442,6 +477,9 @@ 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, "nxp,staggered-outputs"); + /* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions */ regmap_read(pca->regmap, PCA9685_MODE1, ®); reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
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> --- drivers/pwm/pwm-pca9685.c | 62 +++++++++++++++++++++++++++++++-------- 1 file changed, 50 insertions(+), 12 deletions(-)