topic Re: i.mx6 pwm-backlight in i.MX Processors

i.mx6 pwm-backlight

lawrencehuang — Thu, 15 Jan 2015 10:42:55 GMT

how can i add pwm-backlight in my kernel? i use RIoTboard and linux L3.10.17_1.0.0 but can't find where can add it.

thanks!

Re: i.mx6 pwm-backlight

csotoalonso — Thu, 15 Jan 2015 14:50:35 GMT

Hi,

you need to do a couple of things:

Add pwm-backlight support in your kernel, as a built-in module or as a loadable module.
Modify your DTB to add backlight support for your board. As a reference, you could take a look to the imx6qdl-sabresd.dtsi file.

Also, you can see what I did to my board here https://community.freescale.com/thread/337988 It's for a iMX25 board, but the DTB configuration is similar.

Re: i.mx6 pwm-backlight

lawrencehuang — Fri, 16 Jan 2015 02:39:59 GMT

Hi Carlos:

thanks for your reply. but i have some point not understand.

1. in imx6solo_RIoTboard.dts have pwm-backlight

backlight {

compatible = "pwm-backlight";

pwms = <&pwm4 0 5000000>;

brightness-levels = <0 4 8 16 32 64 128 255>;

default-brightness-level = <7>;

2. if modify to use pwm3 (SD1_DATA1) where can modify it. because i can't fine the file in source code. could you give me the fiel path or which way to modify it?

Re: i.mx6 pwm-backlight

art — Thu, 29 Jan 2015 12:48:41 GMT

Please refer to the Section 6.2.2 of the document attached.

Have a great day,
Artur

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Re: i.mx6 pwm-backlight

csotoalonso — Thu, 29 Jan 2015 13:03:18 GMT

Ooops! Totally forgot about it.

If you want to change the PWM device, you don't have to change any source code, just the DTS file for your board. Pretty much as I did for my board:

In the backlight section, change <&pwm4 0 5000000>;to pwm3
Enable pwm3: you need to modify the phandle for pwm3 and change the status to "okay"
In pincontrol, add a group for your pwm and set the correct PAD assignments for your output pin (SD1_DATA1, I presume)

And that's all. As Artur Petukhov pointed out, you'll have your backlight control exported to sysfs, so you can change its brightness value.