PWM signal is at default High state

[Muthyam]

Hello Community,
We are using Apalis IMX8QP/QM in Dunfell Kernel version. I am attaching patch file here.

We are facing an issue regarding backlight pwm, our backlight node is this
&backlight {
default-brightness-level = <4>;
brightness-levels = <0 45 63 88 119 158 203 255>;
pwms = <&pwm_lvds1 0 200000 PWM_POLARITY_INVERTED>;
status = “okay”;
};

While booting PWM signal is going high for around 3 seconds, then it is going low for 2 to 3 seconds, then we are getting pwm on that signal. How can we stop it from going high while booting.

[jimmychan]

In the u-boot, are you set the same pin as PWM? you may try to set it as gpio and output zero in u-boot.

[Muthyam]

I have no idea where those files are located and no idea how to change any uboot files.

[jimmychan · Accepted solution]

In the Yocto folder, the source code of the kernel is located in tmp/work/<board>/linux-imx/<version>/git/. And the u-boot source code is located in tmp/work/<board>/u-boot-imx/<version>/git/.

Then in the u-boot source code, you could use the same device tree file of your board there.

And for example, you could add your code in the <board>.c file to control the gpio output.

for your reference.

https://github.com/nxp-imx/uboot-imx/blob/lf_v2023.04/board/freescale/imx8qm_mek/imx8qm_mek.c