On 07/06/16 09:49, Lothar Waßmann wrote:

Hi,

On Mon, 6 Jun 2016 15:02:21 +0300 Tomi Valkeinen wrote:

quoted

Hi,

On 06/06/16 13:44, Lothar Waßmann wrote:

quoted

'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