how to configure pwm frequency in device tree?

Robotics & Edge Computing Jetson & Embedded Systems Jetson TX2
1

Hi:
We use DP0 as edp interface,use LCD0_BKLT_PWM(B27) as PWM to control lcd’s backlight.
I found some data about PWM in soc/t18x/kernel-dts/tegra186-soc/tegra186-soc-pwm.dtsi.But I couldn’t found the frequency properties.

I use this command to get dts file:
dtc -O dts -I dtb tegra186-quill-p3310-1000-c03-00-base.dtb > /tmp/x.dts

and I found that the status of pwm@3280000,pwm@329000,pwm@32a0000 all "okay",so,I should see the PWM wave on Oscilloscope,but I can't get it.

and my dts is:

#include <t18x-common-platforms/tegra186-quill-common-p3310-1000-a00.dtsi>
#include <t18x-common-platforms/tegra186-quill-power-tree-p3310-1000-a00-00.dtsi>
//#include <t18x-common-platforms/tegra186-quill-camera-modules.dtsi>
#include <t18x-common-modules/tegra186-camera-ar0134-li-mipi-adpt-a00.dtsi>
#include <t18x-common-modules/tegra186-display-e3320-1000-a00.dtsi>

/* comms dtsi file should be included after gpio dtsi file */
#include <t18x-common-platforms/tegra186-quill-comms.dtsi>
#include <t18x-common-plugin-manager/tegra186-quill-p3310-1000-a00-plugin-manager.dtsi>
#include <t18x-common-modules/tegra186-super-module-e2614-p2597-1000-a00.dtsi>
#include <t18x-common-plugin-manager/tegra186-quill-display-plugin-manager.dtsi>
#include <t18x-common-prod/tegra186-priv-quill-p3310-1000-a00-prod.dtsi>
//#include <t18x-common-plugin-manager/tegra186-quill-camera-plugin-manager.dtsi>

#include <dt-bindings/linux/driver-info.h>

the t18x-common-modules/tegra186-camera-ar0134-li-mipi-adpt-a00.dtsi just like t18x-common-platforms/tegra186-quill-camera-modules.dtsi

I have 3 question:

1. the pwm's status is "okay",but I can't get it,so I needed to modify something else?

2. we want to modify the frequency of PWM and the width of High of PWM wave(to control the  brightness of lcd),but I can't found a example under hardware/nvidia. 

3.I found some configuration about pwm,like this:（tegra186-quill-p3310-1000-a00-00-edp.dts)

/* HACK Quill eDP LCD backlight pwm */
		vdd_lcd_bl_pwm: regulator@18 {
			compatible = "regulator-fixed-sync";
			reg = <18>;
			regulator-name = "vdd_lcd_bl_pwm";
			regulator-min-microvolt = <1800000>;
			regulator-max-microvolt = <1800000>;
			enable-active-high;
			gpio = <&tegra_aon_gpio TEGRA_AON_GPIO(U, 0) 1>; /* GPIO_DIS0 for eDP */
			regulator-boot-on;
			regulator-always-on;
		};

on Oscilloscope, the LCD0_BKLT_PWM always be 1, if I change regulator-min-microvolt to <0> ,the output is always be 0. so this configuration just let the B27 to be a GPIO ?

2

XuXiang,

Please refer to this. It is a method to control the pwm manually.

https://devtalk.nvidia.com/default/topic/1026920/jetson-tx2/can-i-control-lcd1_bklt_pwm-/

Yes, you are right. It is set as a GPIO.

3

Thanks.