i.MX8M PWM backlight and CPU idle

cancel
Showing results for 
Search instead for 
Did you mean: 

i.MX8M PWM backlight and CPU idle

731 Views
felixradensky
Contributor IV

On our i.MX8M board we use PWM backlight driver to control display backlight. Below are relevant definitions from the DTS:

backlight: backlight {
        compatible = "pwm-backlight";
        pwms = <&pwm1 0 1000000 0>;
        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 = <80>;

};

&pwm1 {

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

};

pinctrl_pwm1: pwm1grp {
            fsl,pins = <
                MX8MQ_IOMUXC_GPIO1_IO01_PWM1_OUT         0x06
            >;
};

We've found that with backlight enabled CPU cores never enter idle state, causing higher power consumption and temperature. The idle state counter for all cores (/sys/devices/system/cpu/cpuN/cpuidle/state1/usage) is always 0. When backlight is disabled cores enter idle state and board temperature goes down. Setting brightness level to 0 (echo 0 > /sys/devices/platform/backlight/backlight/backlight/brightness) does not help.

Please help us fixing this problem.

Thanks a lot.

Felix.

Labels (2)
0 Kudos
2 Replies

145 Views
felixradensky
Contributor IV

Hi,

Upon further investigation we've come to the conclusion that cpuidle problems are caused by MIPI-DSI. We have disabled all display related hardware components in our DTS (backlight, PWM, DSI-LVDS bridge, touch) leaving only DCSS and MIPI-DSI. The problem still occurs. We don't see this problem when using HDMI display instead of MIPI-CSI. The problem is also reproducible on i.MX8M EVK using  fsl-imx8mq-evk-dcss-rm67191.dtb configuration.

Felix.

145 Views
lily_zhang
NXP Employee
NXP Employee

@Felix_Radensky, we will check it.

0 Kudos