Re: [RFC PATCH v4 2/2] pwm: imx: Configure output to GPIO in disabled state

[Michal VokÃÄ]

On 13.12.2018 09:56, Uwe Kleine-KÃnig wrote:
> On Wed, Dec 12, 2018 at 12:04:51PM +0000, VokÃÄ Michal wrote:
> > Normally the PWM output is held LOW when PWM is disabled. This can cause
> > problems when inverted PWM signal polarity is needed. With this behavior
> > the connected circuit is fed by 100% duty cycle instead of being shut-off.
> >
> > Allow users to define a "pwm" and a "gpio" pinctrl states. The pwm pinctrl
> > state is selected when PWM is enabled and the gpio pinctrl state is
> > selected when PWM is disabled. In the gpio state the new pwm-gpios GPIO is
> > configured as input and the internal pull-up resistor is used to pull the
> > output level high.
> >
> > If all the pinctrl states and the pwm-gpios GPIO are not correctly
> > specified in DT the PWM work as usual.
> >
> > As an example, with this patch a PWM controlled backlight with inversed
> > signal polarity can be used in full brightness range. Without this patch
> > the backlight can not be turned off as brightness = 0 disables the PWM
> > and that in turn set PWM output LOW, that is full brightness.
> >
> > Inverted output of the PWM with "default" and with "pwm"+"gpio" pinctrl:
> >
> > +--------------+------------+---------------+----------- +-------------+
> > | After reset  | Bootloader |   PWM probe   |     PWM    |     PWM     |
> > | 100k pull-up |            |               | enable 30% |   disable   |
> > +--------------+------------+---------------+------------+-------------+
> > | pinctrl      |    none    |    default    |   default  |   default   |
> > | out H   __________________                   __   __                 |
> > | out L                     \_________________/  \_/  \_/\____________ |
> > |                                           ^    ^    ^                |
> > +--------------+------------+---------------+------------+-------------+
> > | pinctrl      |    none    |      gpio     |     pwm    |     gpio    |
> > | out H   __________________________________   __   __   _____________ |
> > | out L                                     \_/  \_/  \_/              |
> > |                                           ^    ^    ^                |
> > +----------------------------------------------------------------------+
>
> Just for the record: My last concern against this patch set (that I sent
> for v3) and v4 of the series criss-crossed. So the problem with the
> peaks that could happen is still unaddressed.

Hi Uwe et al.

Sorry for the huge delay. I hope we will be able to refresh our
memories and continue on the discussion. I will react to your
comments in the appropriate v3 thread. And sorry for this v4.
I was too fast on the trigger back then..

Michal