Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero

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From	Tomi Valkeinen <tomi.valkeinen@ti.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero
Date	Tue, 07 Jun 2016 10:10:01 +0200
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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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[PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero Lothar Waßmann <LW@KARO-electronics.de> - 2016-06-06 12:50 +0200
  Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero Tomi Valkeinen <tomi.valkeinen@ti.com> - 2016-06-06 14:10 +0200
    Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is  zero Lothar Waßmann <LW@KARO-electronics.de> - 2016-06-07 08:50 +0200
      Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero Tomi Valkeinen <tomi.valkeinen@ti.com> - 2016-06-07 10:10 +0200

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