| Message ID | 1465209896-10319-1-git-send-email-LW@KARO-electronics.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi, On 06/06/16 13:44, Lothar Waßmann wrote: > 'brightness' is usually an index into a table of duty_cycle values, > where the value at index 0 may well be non-zero > (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life > examples). > Thus brightness == 0 does not necessarily mean that the PWM output > will be inactive. > Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide > whether to disable the PWM. The binding doc does say: - brightness-levels: Array of distinct brightness levels. Typically these are in the range from 0 to 255, but any range starting at 0 will do. The actual brightness level (PWM duty cycle) will be interpolated from these values. 0 means a 0% duty cycle (darkest/off), while the last value in the array represents a 100% duty cycle (brightest). Tomi
Hi, On Mon, 6 Jun 2016 15:02:21 +0300 Tomi Valkeinen wrote: > Hi, > > On 06/06/16 13:44, Lothar Waßmann wrote: > > 'brightness' is usually an index into a table of duty_cycle values, > > where the value at index 0 may well be non-zero > > (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life > > examples). > > Thus brightness == 0 does not necessarily mean that the PWM output > > will be inactive. > > Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide > > whether to disable the PWM. > > The binding doc does say: > > - brightness-levels: Array of distinct brightness levels. Typically these > are in the range from 0 to 255, but any range starting at 0 will do. > The actual brightness level (PWM duty cycle) will be interpolated > from these values. 0 means a 0% duty cycle (darkest/off), while the > last value in the array represents a 100% duty cycle (brightest). > So, what should I do, when I need a range of levels that doesn't start at 0? E.g. if the brightness is inverse proportional to the PWM duty cycle. Lothar Waßmann -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 07/06/16 09:49, Lothar Waßmann wrote: > Hi, > > On Mon, 6 Jun 2016 15:02:21 +0300 Tomi Valkeinen wrote: >> Hi, >> >> On 06/06/16 13:44, Lothar Waßmann wrote: >>> 'brightness' is usually an index into a table of duty_cycle values, >>> where the value at index 0 may well be non-zero >>> (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life >>> examples). >>> Thus brightness == 0 does not necessarily mean that the PWM output >>> will be inactive. >>> Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide >>> whether to disable the PWM. >> >> The binding doc does say: >> >> - brightness-levels: Array of distinct brightness levels. Typically these >> are in the range from 0 to 255, but any range starting at 0 will do. >> The actual brightness level (PWM duty cycle) will be interpolated >> from these values. 0 means a 0% duty cycle (darkest/off), while the >> last value in the array represents a 100% duty cycle (brightest). >> > So, what should I do, when I need a range of levels that doesn't start > at 0? E.g. if the brightness is inverse proportional to the PWM duty > cycle. That's a question to the PWM/backlight maintainers, but I think in the addition of your patch, the binding doc needs to be changed, as it doesn't hold true after your patch. Tomi
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index b2b366b..80b2b52 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -103,8 +103,8 @@ static int pwm_backlight_update_status(struct backlight_device *bl) if (pb->notify) brightness = pb->notify(pb->dev, brightness); - if (brightness > 0) { - duty_cycle = compute_duty_cycle(pb, brightness); + duty_cycle = compute_duty_cycle(pb, brightness); + if (duty_cycle > 0) { pwm_config(pb->pwm, duty_cycle, pb->period); pwm_backlight_power_on(pb, brightness); } else
'brightness' is usually an index into a table of duty_cycle values, where the value at index 0 may well be non-zero (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life examples). Thus brightness == 0 does not necessarily mean that the PWM output will be inactive. Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide whether to disable the PWM. Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de> --- drivers/video/backlight/pwm_bl.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)