how do I run an lvds display with the LP8551 backlight driver

Chip Platform Rockchip
1

hello, please tell me which DTS to take and how to edit it to run the LVDS display with the LP8551 backlight driver

2

Help! I’ll give you a bowl of rice and a cat wife

3

Good luck.
https://gitlab.com/firefly-linux/kernel/-/blob/rk356x/firefly/Documentation/devicetree/bindings/pwm/pwm-lp3943.txt?ref_type=heads
https://gitlab.com/firefly-linux/kernel/-/blob/rk356x/firefly/drivers/video/backlight/lp855x_bl.c?ref_type=heads

4

thanks for the links. I have a problem at the moment: I can’t turn on GPIO3_B0 to turn on the power for the I2C backlight controller, as it can be done correctly in dts. the LP855x driver starts, but there is no power and i2c on the board, it cannot configure.
P.S.one more question: is it necessary to use lp3943@60?

5

After the pin is applied by the driver, you cannot directly control it at the system layer, and the driver needs to provide a control interface.
According to the specifications and functions of the LP855X chip, add the corresponding attributes to dts. These properties can include register addresses, power controls, brightness controls, etc.
You can find some examples online.

lp8551@60 {
    compatible = "ti,lp8551";
    reg = <0x60>;
    reg-names = "lp8551";
    enable-gpios = <&gpio 0 GPIO_ACTIVE_HIGH>;
    brightness-levels = <0 64 128 192 255>;
    default-brightness-level = <255>;
    ...
};

https://gitlab.com/firefly-linux/kernel/-/blob/rk356x/firefly/Documentation/devicetree/bindings/leds/backlight/lp855x.txt?ref_type=heads

6

thanks for the reply. is there a document describing GPIO RK3568, because enabling GPIO3_B0 does not give a result, I have suspicions that it does not relate to MIPI0_DSI0/LVDS in any way

7

Paquq Posted at 9/7/2023 20:24
thanks for the reply. is there a document describing GPIO RK3568, because enabling GPIO3_B0 does not …

https://wiki.t-firefly.com/en/Core-3568J/driver_gpio.html

8

I found the necessary GPIOs, enable them using /sys/class/gpio, and i2c works. I have specified the necessary GPIOs in dts, but they do not turn on at boot, so the driver does not work either. part of the DTS and the log is attached.

DTS:

&i2c1 {
#address-cells = <1>;
#size_cells = <0>;

backlight: backlight@2c {
// compatible = “pwm-backlight”;

  compatible = "ti,lp8551";
  reg = <0x2c>;
  bl-name = "lcd-bl";

  enable-gpios = <&gpio0 RK_PC3 GPIO_ACTIVE_LOW>, <&gpio4 RK_PC5 GPIO_ACTIVE_HIGH>; //pin-pwm - low; bl_en - high

  pwms = <&pwm4 0 25000 0>;
  brightness-levels = <
  	  0  20  20  21  21  22  22  23
  	...............................
  	248 249 250 251 252 253 254 255
  >;
  default-brightness-level = <200>;

};
};

KERNEL LOG:
root@firefly:~# dmesg | grep lp855
[ 1.381622] lp855x 1-002c: Looking up power-supply from device tree
[ 1.381636] lp855x 1-002c: Looking up power-supply property in node /i2c@fe5a0000/backlight@2c failed
[ 1.381673] lp855x 1-002c: 1-002c supply power not found, using dummy regulator
[ 1.381789] lp855x 1-002c: Linked as a consumer to regulator.0
[ 1.381823] lp855x 1-002c: Looking up enable-supply from device tree
[ 1.381837] lp855x 1-002c: Looking up enable-supply property in node /i2c@fe5a0000/backlight@2c failed
[ 1.382048] lp855x 1-002c: device config err: -6
[ 1.382147] lp855x 1-002c: Dropping the link to regulator.0

9

thank you very much, everything worked, helped a lot

10

Running an LVDS display with the LP8551 backlight driver can be tricky, especially when configuring drivers on Linux. For remote troubleshooting or accessing secure online resources while working on such projects, it’s helpful to buy VPN with credit card to ensure private and secure internet access during the process.