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PWM on iMX.25

Question asked by Carlos Soto on Dec 31, 2014
Latest reply on Jan 14, 2015 by Fabio Estevam

Hi,

I'm trying to enable PWM in the DTS of my KaRo TX25 module, with kernel 3.17.2, but it does not seem to work. I've created a PWM Backlight so I can control it through /sys/class/backlight, but when I change the brightness value, nothing happens, even though the value of actual_brightness is correctly updated.

 

Here are the relevant parts of my DTS:

 

backlight:

backlight: backlight5110 {

        compatible = "pwm-backlight";

        pwms = <&pwm1 0 500000>;

        power-supply = <&reg_lcd_3v3>;

        pwm-names = "backlight-5110";

        brightness-levels = <

              0  1  2  3  4  5  6  7  8  9

             10 11 12 13 14 15 16 17 18 19

             20 21 22 23 24 25 26 27 28 29

             30 31 32 33 34 35 36 37 38 39

             40 41 42 43 44 45 46 47 48 49

             50 51 52 53 54 55 56 57 58 59

             60 61 62 63 64 65 66 67 68 69

             70 71 72 73 74 75 76 77 78 79

             80 81 82 83 84 85 86 87 88 89

             90 91 92 93 94 95 96 97 98 99

            100

        >;

        default-brightness-level = <50>;

    };

 

PWM:

&pwm1 {

    pinctrl-names = "default";

    pinctrl-0 = <&pinctrl_pwm1>;

    #pwm-cells = <2>;

};

 

Pincontrol:

pinctrl_pwm1: pwmgrp {

            fsl,pins = <

                /* MX25_PAD_PWM__PWM                    0x190  */

                /* MX25_PAD_PWM__GPIO_1_26                0x190  */

                MX25_PAD_PWM__GPIO_1_26                0x80000000

            >;           

        };

 

When I export the pin as GPIO, it works fine. I'm able to control it through /sys/class/gpio and the display backlight is correctly lit on and off, but when I try to use PWM it doesn't change.

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