i.MX Processors中的主题 Re: I.MX6Q Custom Device Tree - Backlight not working

I.MX6Q Custom Device Tree - Backlight not working

PaulDeMetrotion — Tue, 15 Dec 2015 23:47:15 GMT

I have developed a custom device tree that has two LVDS outputs with independent backlights. Neither of the backlights get enabled or configured. Below is the device tree entries. Any idea what I am missing? Thanks in advance.

backlight {
	backlight-0 {
		compatible = "pwm-backlight";
		pwms = <&pwm1 0 5000000>;
		brightness-levels = <0 4 8 16 32 64 128 255>;
		default-brightness-level = <7>;
		enable-gpios = <&gpio1 5 0>;
	};

	backlight-1 {
		compatible = "pwm-backlight";
		pwms = <&pwm2 0 5000000>;
		brightness-levels = <0 4 8 16 32 64 128 255>;
		default-brightness-level = <7>;
		enable-gpios = <&gpio7 13 0>;
	};
};

&pwm1 {

	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_pwm1>;
	status = "okay";

};

&pwm2 {

	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_pwm2>;
	status = "okay";

};

pinctrl_pwm1: pwm1grp {
	fsl,pins = <
		MX6QDL_PAD_GPIO_9__PWM1_OUT 0x1b0b1 // backlight lvds1
	>;
};

pinctrl_pwm2: pwm2grp {
	fsl,pins = <
		MX6QDL_PAD_DISP0_DAT9__PWM2_OUT 0x1b0b1 // backlight lvds2
	>;
};

Re: I.MX6Q Custom Device Tree - Backlight not working

igorpadykov — Wed, 16 Dec 2015 02:33:21 GMT

Hi Paul

for pwm dts configuration one can look at

linux-2.6-imx.git - Freescale i.MX Linux Tree

Best regards

igor

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Re: I.MX6Q Custom Device Tree - Backlight not working

PaulDeMetrotion — Thu, 17 Dec 2015 15:40:37 GMT

I have almost solved this issue. I am new to the device tree world, but I thought that the device tree configurations would set up the device according to my custom settings. I had to add code to my custom u-boot file to actually configure the PWM registers. After doing this the LVDS backlight was functional.

This leads to a larger question: How is the device tree data used by the kernel to configure the specific functions in the device? Where in the kernel boot process is the DTB file used?