i.mx6 pwm-backlight

[lawrencehuang]

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!

[art]

Please refer to the Section 6.2.2 of the document attached.

Have a great day,
Artur

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[csotoalonso]

Hi,

you need to do a couple of things:

1. Add pwm-backlight support in your kernel, as a built-in module or as a loadable module.
2. 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.

[lawrencehuang]

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?

[csotoalonso · Accepted solution]

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:

1. In the backlight section, change <&pwm4 0 5000000>;to pwm3
2. Enable pwm3:  you need to modify the phandle for pwm3 and change the status to "okay"
3. 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.