Messages in this thread | | | From | Michal Vokáč <> | Subject | Re: [RFC PATCH v4 2/2] pwm: imx: Configure output to GPIO in disabled state | Date | Thu, 24 Jan 2019 09:54:16 +0100 |
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On 13.12.2018 09:56, Uwe Kleine-König wrote: > 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.
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
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