TI AM5728 LCD Touchscreen Driver Porting and DTS Configuration

Adding an LCD screen to the Sienovo XM5728-IDK-V3 development board. The result after successful integration:

References: Porting LCD on AM335x using DTS (Part 1) https://blog.csdn.net/xiaojiezuo123/article/details/49890733

For driver source code, add WeChat: 13670212541, technical discussions are welcome.

Debugging Experience/Notes:

Development Environment: Using Sienovo AM5728 core board, the board is self-developed by the company, LCD models are: AT080TN64, AT070TN94

Issues encountered:

1. No /dev/fb0 device node was created.

2. LCD text display order was reversed.

3. LCD colors were incorrect.

The 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>;
            };
        };
    };
};

Analyzing the causes of the issues:

In the kernel print messages, repeatedly appeared: Linked as a consumer to regulator.20 Dropping the link to regulator.20
Pinmux settings for the LCD were incorrect.
The driver corresponding to compatible = "panel-dpi" in the device driver had issues.
Setting .bus_format = MEDIA_BUS_FMT_RGB888_1X24 in the driver, which can change the RGB data format and output RGB data in different formats.
Hardware issues with the LCD driver board.
Issues with the LCD output timing.

Problem-solving process:

regulator.20 is located under the /sys/class/regulator/ device node, the voltage is 1.8V, and multimeter measurements also showed it to be normal.
Even after configuring pinmux in the device tree, no node was generated.
Upon checking the driver directory corresponding to panel-dpi, it was found that this driver was not compiled, so there might be an issue with device matching.
Changing the format to BGR, GRB, etc., did not change the display effect.
Measured whether the pins on the LCD driver board and the core board were connected.
Used an oscilloscope to check if the LCD output timing was incorrect.

Issues resolved:

1. By changing compatible to compatible = "osddisplays,osd070t1718-19ts", "panel-dpi";, the /dev/fb0 device node can be generated.

2. LCD colors were incorrect; measuring the voltage with a multimeter, it was found that the IO voltage of the LCD driver board was too high. The hardware team just needed to add a resistor to the driver board.