Re: [PATCH 1/2] PWM: let of_xlate handlers check args count

[Sascha Hauer]

On Fri, Jan 24, 2014 at 06:42:54AM +0100, Lothar Waßmann wrote:
> Hi,
> 
> > Okay, this works, but there's a problem with pwm-leds.
> > 
> > When the duty cycle is set to zero (when you set the brightness to zero)
> > pwm-leds decides to disable the PWM after configuring it.  This causes
> > the PWM output to be driven low, causing the LED to go to maximum
> > brightness.
> > 
> > So, using the inversion at PWM level doesn't work.
> > 
> The problem is that the driver calls pwm_disable() when the duty cycle is 0.
> This sets the PWM output low independent from the output polarity setting.
> 
> > To make this work correctly, we really need pwm-leds to do the inversion
> > rather than setting the inversion bit in hardware.
> > 
> The same holds for the pwm-backlight driver.
> 
> The easiest fix would be not to call pwm_disable() even for a zero duty
> cycle.

IMO that's the right thing to do anyway due to the different PWM
hardware controllers we have. I'm thinking about the following patch
for some time.

Sascha

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