How to use timers2 as pwm-backlight?

SChen.11 · ‎2019-06-07

HI, I needs use timers2 to enable the pwm function. Then it will used as pwm-backlight for LCD. I wasn't known how to write the dts file. Could you show me some example code on this function?

Bernard PUEL · ‎2019-06-13

Could you please try this declaration and use &pwm2 phandle in your pwms declaration ( pwms = <&pwm2 0 5000000>;):

503 &timers2 {

504 status = "okay";

505 /* spare dmas for other usage */

506 /delete-property/dmas;

507 /delete-property/dma-names;

508 - pwm {

+ pwm2: pwm {

509 pinctrl-0 = <&pwm2_pins_a>;

510 pinctrl-1 = <&pwm2_sleep_pins_a>;

511 pinctrl-names = "default", "sleep";

512 #pwm-cells = <2>;

513 status = "okay";

514 };

515 - timer@1 {

516 - status = "disabled";

517 - };

518 };

View solution in original post

PatrickF · ‎2019-06-09

You could find some details in https://wiki.st.com/stm32mpu/wiki/TIM_device_tree_configuration and https://wiki.st.com/stm32mpu/wiki/PWM_overview

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SChen.11 · ‎2019-06-11

Hi PatrickF Thanks. I got this error message.

 Warning (pwms_property): /panel-backlight: Missing property '#pwm-cells' in node /soc/timer@40000000 or bad phandle (referred from pwms[0])

Here is my backlight dts code

187         panel_backlight: panel-backlight {
188                 compatible = "pwm-backlight";
189                 pwms = <&timers2 0 5000000>;
190                 brightness-levels = <0 4 8 16 32 64 128 255>;
191                 default-brightness-level = <6>;
192                 status = "okay";
193         };

It seems my "pwms" value was wrong.

Bernard PUEL · ‎2019-06-12

You have first to configure your pinctrl of your pwm output like described in this article (remove the trigger source part):

https://wiki.st.com/stm32mpu/wiki/TIM_device_tree_configuration#TIM_configured_in_PWM_mode_and_trigger_source

Then you will need to use your &pwm1_pins_a phandle defined instead of &timers2 above. see:

https://github.com/STMicroelectronics/linux/blob/v4.19-stm32mp/Documentation/devicetree/bindings/pwm/pwm.txt

As you will use in your backlight declaration 2 arguments (pwms = <&pwm1_pins_a 0 5000000>;), you will need to add this property in your pwm node:

#pwm-cells = <2>;

Hoping it is clear.

SChen.11 · ‎2019-06-13

503 &timers2 {
504         status = "okay";
505         /* spare dmas for other usage */
506         /delete-property/dmas;
507         /delete-property/dma-names;
508         pwm {
509                 pinctrl-0 = <&pwm2_pins_a>;
510                 pinctrl-1 = <&pwm2_sleep_pins_a>;
511                 pinctrl-names = "default", "sleep";
512                 #pwm-cells = <2>;
513                 status = "okay";
514         };
515         timer@1 {
516                 status = "disabled";
517         };
518 };
 
 
187         panel_backlight: panel-backlight {
188                 compatible = "pwm-backlight";
189                 pwms = <&pwm2_pins_a 0 5000000>;
190                 brightness-levels = <0 4 8 16 32 64 128 255>;
191                 default-brightness-level = <6>;
192                 status = "okay";
193         };

I add the "pwm-cell" attribute to timers2 block. Then I use pwm2_pins_a also has the warning info.

Warning (pwms_property): /panel-backlight: Missing property '#pwm-cells' in node /soc/pin-controller@50002000/pwm2-0 or bad phandle (referred from pwms[0])

Bernard PUEL · ‎2019-06-13