lkml.org 
[lkml]   [2019]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [RFC PATCH v4 2/2] pwm: imx: Configure output to GPIO in disabled state
Date
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

\
 
 \ /
  Last update: 2019-01-24 10:00    [W:0.054 / U:0.524 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site