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
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