| Message ID | 20220427184513.21192-1-eajames@linux.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | [linux,dev-5.15] leds: pca955x: Set blink duty cycle to fifty percent | expand |
Dear Eddie, Am 27.04.22 um 20:45 schrieb Eddie James: > In order to blink at the specified rate, the blinking LEDs > need to maintain a 50% duty cycle. Therefore, don't use PWM0 > for any attempted brightness change, and set PWM0 when > enabling blinking. Is that specified in some datasheet? Nit: I’d write 50 % in the commit message summary. Kind regards, Paul > Signed-off-by: Eddie James <eajames@linux.ibm.com> > --- > drivers/leds/leds-pca955x.c | 17 ++++++++++------- > 1 file changed, 10 insertions(+), 7 deletions(-) > > diff --git a/drivers/leds/leds-pca955x.c b/drivers/leds/leds-pca955x.c > index 2570f92b6754..da93f04e4d10 100644 > --- a/drivers/leds/leds-pca955x.c > +++ b/drivers/leds/leds-pca955x.c > @@ -289,17 +289,12 @@ static enum led_brightness pca955x_led_get(struct led_classdev *led_cdev) > > switch (pca955x_ledstate(ls, pca955x_led->led_num % 4)) { > case PCA955X_LS_LED_ON: > + case PCA955X_LS_BLINK0: > ret = LED_FULL; > break; > case PCA955X_LS_LED_OFF: > ret = LED_OFF; > break; > - case PCA955X_LS_BLINK0: > - ret = pca955x_read_pwm(pca955x, 0, &pwm); > - if (ret) > - return ret; > - ret = 256 - pwm; > - break; > case PCA955X_LS_BLINK1: > ret = pca955x_read_pwm(pca955x, 1, &pwm); > if (ret) > @@ -332,7 +327,7 @@ static int pca955x_led_set(struct led_classdev *led_cdev, > clear_bit(pca955x_led->led_num, &pca955x->active_blink); > ls = pca955x_ledsel(ls, bit, PCA955X_LS_LED_OFF); > } else { > - ret = pca955x_write_pwm(pca955x, 0, 256 - value); > + /* No variable brightness for blinking LEDs */ > goto out; > } > } else { > @@ -432,6 +427,14 @@ static int pca955x_led_blink(struct led_classdev *led_cdev, > ret = pca955x_write_ls(pca955x, reg, ls); > if (ret) > goto out; > + > + /* > + * Force 50% duty cycle to maintain the specified > + * blink rate. > + */ > + ret = pca955x_write_pwm(pca955x, 0, 128); > + if (ret) > + goto out; > } > > if (pca955x->blink_period != p) {
On 4/28/22 10:12, Paul Menzel wrote: > Dear Eddie, > > > Am 27.04.22 um 20:45 schrieb Eddie James: >> In order to blink at the specified rate, the blinking LEDs >> need to maintain a 50% duty cycle. Therefore, don't use PWM0 >> for any attempted brightness change, and set PWM0 when >> enabling blinking. > > Is that specified in some datasheet? It is in the PCA955X datasheets (https://www.nxp.com/docs/en/data-sheet/PCA9552.pdf) but it's not exactly clear. The relationship between the PWM rate and the blink rate is not specified, but for example, setting maximum duty cycle and 1 second blink period results in the LED not blinking. Setting 50% duty cycle blinks the LED at 1 second intervals, as expected. > > Nit: I’d write 50 % in the commit message summary. Ah ok. Thanks! Eddie > > > Kind regards, > > Paul > > >> Signed-off-by: Eddie James <eajames@linux.ibm.com> >> --- >> drivers/leds/leds-pca955x.c | 17 ++++++++++------- >> 1 file changed, 10 insertions(+), 7 deletions(-) >> >> diff --git a/drivers/leds/leds-pca955x.c b/drivers/leds/leds-pca955x.c >> index 2570f92b6754..da93f04e4d10 100644 >> --- a/drivers/leds/leds-pca955x.c >> +++ b/drivers/leds/leds-pca955x.c >> @@ -289,17 +289,12 @@ static enum led_brightness >> pca955x_led_get(struct led_classdev *led_cdev) >> switch (pca955x_ledstate(ls, pca955x_led->led_num % 4)) { >> case PCA955X_LS_LED_ON: >> + case PCA955X_LS_BLINK0: >> ret = LED_FULL; >> break; >> case PCA955X_LS_LED_OFF: >> ret = LED_OFF; >> break; >> - case PCA955X_LS_BLINK0: >> - ret = pca955x_read_pwm(pca955x, 0, &pwm); >> - if (ret) >> - return ret; >> - ret = 256 - pwm; >> - break; >> case PCA955X_LS_BLINK1: >> ret = pca955x_read_pwm(pca955x, 1, &pwm); >> if (ret) >> @@ -332,7 +327,7 @@ static int pca955x_led_set(struct led_classdev >> *led_cdev, >> clear_bit(pca955x_led->led_num, &pca955x->active_blink); >> ls = pca955x_ledsel(ls, bit, PCA955X_LS_LED_OFF); >> } else { >> - ret = pca955x_write_pwm(pca955x, 0, 256 - value); >> + /* No variable brightness for blinking LEDs */ >> goto out; >> } >> } else { >> @@ -432,6 +427,14 @@ static int pca955x_led_blink(struct led_classdev >> *led_cdev, >> ret = pca955x_write_ls(pca955x, reg, ls); >> if (ret) >> goto out; >> + >> + /* >> + * Force 50% duty cycle to maintain the specified >> + * blink rate. >> + */ >> + ret = pca955x_write_pwm(pca955x, 0, 128); >> + if (ret) >> + goto out; >> } >> if (pca955x->blink_period != p) {
diff --git a/drivers/leds/leds-pca955x.c b/drivers/leds/leds-pca955x.c index 2570f92b6754..da93f04e4d10 100644 --- a/drivers/leds/leds-pca955x.c +++ b/drivers/leds/leds-pca955x.c @@ -289,17 +289,12 @@ static enum led_brightness pca955x_led_get(struct led_classdev *led_cdev) switch (pca955x_ledstate(ls, pca955x_led->led_num % 4)) { case PCA955X_LS_LED_ON: + case PCA955X_LS_BLINK0: ret = LED_FULL; break; case PCA955X_LS_LED_OFF: ret = LED_OFF; break; - case PCA955X_LS_BLINK0: - ret = pca955x_read_pwm(pca955x, 0, &pwm); - if (ret) - return ret; - ret = 256 - pwm; - break; case PCA955X_LS_BLINK1: ret = pca955x_read_pwm(pca955x, 1, &pwm); if (ret) @@ -332,7 +327,7 @@ static int pca955x_led_set(struct led_classdev *led_cdev, clear_bit(pca955x_led->led_num, &pca955x->active_blink); ls = pca955x_ledsel(ls, bit, PCA955X_LS_LED_OFF); } else { - ret = pca955x_write_pwm(pca955x, 0, 256 - value); + /* No variable brightness for blinking LEDs */ goto out; } } else { @@ -432,6 +427,14 @@ static int pca955x_led_blink(struct led_classdev *led_cdev, ret = pca955x_write_ls(pca955x, reg, ls); if (ret) goto out; + + /* + * Force 50% duty cycle to maintain the specified + * blink rate. + */ + ret = pca955x_write_pwm(pca955x, 0, 128); + if (ret) + goto out; } if (pca955x->blink_period != p) {
In order to blink at the specified rate, the blinking LEDs need to maintain a 50% duty cycle. Therefore, don't use PWM0 for any attempted brightness change, and set PWM0 when enabling blinking. Signed-off-by: Eddie James <eajames@linux.ibm.com> --- drivers/leds/leds-pca955x.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)