Development Environment: Using Xinmai AM5728 core board, custom-made board, LCD models: AT080TN64, AT070TN94

Problems Encountered:

1. The /dev/fb0 device node is not created

2. LCD character display order is reversed

3. LCD color display is incorrect

LCD-related configuration in the device tree is as follows:

aliases {
    display1 = &lcd;
    rtc0 = &tps659038_rtc;
    rtc1 = &isl1208_rtc;
};

lcd_bl: backlight {
    compatible = "pwm-backlight";
    pwms = <&ecap0 0 50000 0>;
    brightness-levels = <0 51 53 56 62 75 101 152 255>;
    default-brightness-level = <8>;
};

lcd: display {
    compatible = "osddisplays,osd070t1718-19ts", "panel-dpi";
    enable-gpios = <&gpio3 30 GPIO_ACTIVE_HIGH>;
    backlight = <&lcd_bl>;
    label = "lcd";

    panel-timing {
        clock-frequency = <33300000>;
        hactive = <800>;
        vactive = <480>;
        hfront-porch = <210>;
        hback-porch = <46>;
        hsync-len = <20>;
        vfront-porch = <22>;
        vback-porch = <23>;
        vsync-len = <10>;
        hsync-active = <1>;
        vsync-active = <1>;
        de-active = <0>;
        pixelclk-active = <0>;
    };

    port {
        lcd_in: endpoint {
            remote-endpoint = <&dpi_out>;
        };
    };
};

&dss {
    status = "okay";
    vdda_video-supply = <&ldoln_reg>;
    ports {
        #address-cells = <1>;
        #size-cells = <0>;
        port {
            reg = <1>;
            dpi_out: endpoint {
                data-lines = <24>;
                remote-endpoint = <&lcd_in>;
            };
        };
    };
};

Analysis of Root Causes:

Kernel log repeatedly shows: "Linked as a consumer to regulator.20" followed by "Dropping the link to regulator.20"
Incorrect pinmux configuration for the LCD
Issue with the driver corresponding to the compatible string "panel-dpi"
Setting the driver's .bus_format = MEDIA_BUS_FMT_RGB888_1X24 can alter the RGB data format, enabling output of different RGB formats
Hardware issue on the LCD driver board
Incorrect LCD output timing

Troubleshooting Process:

Regulator.20 corresponds to the device node under /sys/class/regulator/, with a voltage of 1.8V, which was confirmed correct using a multimeter
Even after configuring pinmux in the device tree, the device node still did not appear
Upon checking the driver directory corresponding to panel-dpi, it was found that the driver was not compiled — indicating a device matching issue
Changing the format to BGR, GRB, etc., had no effect on display output
Measured continuity between pins on the LCD driver board and the core board
Used an oscilloscope to verify whether the LCD output timing was correct

Issues Resolved:

1. Changing the compatible string to compatible = "osddisplays,osd070t1718-19ts", "panel-dpi"; successfully generates the /dev/fb0 device node

2. Incorrect LCD color display was traced via multimeter to excessive IO voltage on the LCD driver board; adding a resistor on the driver board, as advised by the hardware team, resolved the issue