Hello, On Wed, Dec 12, 2018 at 12:04:51PM +0000, Vokáč 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. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |
