i.MX ProcessorsのトピックRe: How to control pwm backlight on imx8mplus platform

How to control pwm backlight on imx8mplus platform

t2865k5 — Mon, 25 Dec 2023 10:58:13 GMT

Dear NXP ,

SW version :

repo init -u https://github.com/nxp-imx/imx-manifest -b imx-linux-langdale -m imx-6.1.1-1.0.1.xml

HW : imx8mplus

The LVDS panel can display normally. I want to control pwm backlight .

GPIO1_IO11 : pwm backlight

Please refer to my imx8mp-evk.dts :

lvds_backlight: lvds_backlight {

compatible = "pwm-backlight";

pwms = <&pwm2 0 100000 0>;

status = "okay";

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>;

};

lvds0_panel {
compatible = "panel-lvds";
backlight = <&lvds_backlight>;
power-supply = <&reg_lvds_pwr>;
data-mapping = "jeida-18";
data-width = <18>;
height-mm = <135>; /* 135.6 */
width-mm = <216>; /* 216.96 */
panel-timing {
clock-frequency = <74250000>;
hactive = <1280>;
vactive = <800>;
hback-porch = <64>;
hfront-porch = <42>;
vback-porch = <49>;
vfront-porch = <20>;
hsync-len = <22>;
vsync-len = <20>;
};
port {
panel_lvds_in: endpoint {
remote-endpoint = <&lvds_out>;
};
};
};

&pwm2 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_pwm2>;
status = "okay";
};

pinctrl_pwm2: pwm2grp {

fsl,pins = <

MX8MP_IOMUXC_GPIO1_IO11__PWM2_OUT 0x116

};

cat max_brightness : This value is 100

cat brightness : This value is 80

echo 0 > brightness

cat brightness : This value is 0 but the LVDS panel can still display normally.

I use an oscilloscope to measure the PWM voltage . It always keep 3.3 V .

I add some log in pwm_bl.c .Please refer the pwm_backlight.log and pwm_bl.c .

Please help to solve this problem .

Re: How to control pwm backlight on imx8mplus platform

Zhiming_Liu — Wed, 27 Dec 2023 02:50:33 GMT

Please verify this with Oscilloscope and provide full dts file.

Re: How to control pwm backlight on imx8mplus platform

t2865k5 — Sun, 31 Dec 2023 08:49:55 GMT

Dear Zhiming ,

Please refer to the device tree I provided .

Re: How to control pwm backlight on imx8mplus platform

Zhiming_Liu — Tue, 02 Jan 2024 02:28:08 GMT

Here is my test with same pwm node on EVK board.

Brightness=10

Brightness=1

Brightness =0

You can see that the PWM voltage is zero when brightness=0.

Re: How to control pwm backlight on imx8mplus platform

t2865k5 — Thu, 04 Jan 2024 03:42:45 GMT

Dear Zhiming,

I use GPIO1_IO11 to config PWM .

set

Brightness =10

Brightness =1

Brightness =0

PWM voltage always keep 3.3V.

Plese help to check my device tree whether it needs to be modified .

&pwm1 {

pinctrl-names = "default";

pinctrl-0 = <&pinctrl_pwm1>;

status = "okay";

};

&pwm2 {

pinctrl-names = "default";

pinctrl-0 = <&pinctrl_pwm2>;

status = "okay";

};

&pwm4 {

pinctrl-names = "default";

pinctrl-0 = <&pinctrl_pwm4>;

status = "okay";

};

pinctrl_pwm1: pwm1grp {

fsl,pins = <

MX8MP_IOMUXC_GPIO1_IO01__PWM1_OUT 0x116

};

pinctrl_pwm2: pwm2grp {

fsl,pins = <

MX8MP_IOMUXC_GPIO1_IO11__PWM2_OUT 0x116

};

pinctrl_pwm4: pwm4grp {

fsl,pins = <

MX8MP_IOMUXC_SAI5_RXFS__PWM4_OUT 0x116

};

Re: How to control pwm backlight on imx8mplus platform

Zhiming_Liu — Fri, 05 Jan 2024 07:15:06 GMT

From the hardware desgin you attached, the PWM will be pull up with the VDDEXT_3V3, so this is normal. You can remove R2389 to get low value when brightness =0.