How to use HDMI to 4 lane MIPI DSI adapter with Jetson Nano?

How to Use HDMI to 4 Lane MIPI DSI Adapter with Jetson Nano

To get an HDMI to 4 lane MIPI DSI adapter working with a Jetson Nano, you need to connect the adapter to the Nano’s 40-pin GPIO header or a dedicated MIPI DSI connector, configure the device tree, and power the adapter correctly. The Jetson Nano has a 15-pin MIPI DSI interface on the carrier board, but it’s often used for the official 7-inch display. For third-party panels, you’ll need an hdmi to 4 lane mipi dsi adapter that converts HDMI signals to the MIPI DSI protocol. This adapter typically includes a bridge chip like the LT8918 or TC358870, which handles the signal conversion. The Nano’s MIPI interface supports up to 4 lanes, running at 1.5 Gbps per lane, giving a total bandwidth of about 6 Gbps, which is enough for 1080p at 60 Hz. The adapter’s HDMI input accepts up to 4K at 30 Hz, but the MIPI output is limited by the Nano’s DSI controller, so you’ll likely get 1080p at 60 Hz or 720p at 60 Hz depending on the panel.

First, check your Jetson Nano revision. The original A02 and B01 boards have a 15-pin FPC connector for MIPI DSI, while the newer Jetson Nano 2GB Developer Kit uses a different pinout. The adapter’s datasheet should specify compatibility. For the A02/B01, the connector is J13, with pin 1 marked by a triangle. The pinout includes 4 data lanes (D0 to D3), a clock lane, power (3.3V and 1.8V), and ground. The adapter needs a 5V or 12V power supply, depending on the model, because the bridge chip and panel backlight draw more current than the Nano’s GPIO can provide. The official display uses 3.3V, but many adapters require an external 5V/2A supply. For example, the LT8918-based adapter needs 5V at 500 mA for the chip plus up to 1.5A for the backlight, so a 5V/2A wall adapter is common. Connect the adapter’s power input to a separate supply, not the Nano’s 5V pin, to avoid overloading the Nano’s regulator.

Now, the physical connection. The adapter’s output is a 30-pin or 40-pin FPC connector for the MIPI DSI cable. The Jetson Nano’s MIPI connector is a 15-pin, 0.5mm pitch FPC, so you’ll need a ribbon cable that matches both sides. Many adapters come with a 15-pin to 30-pin cable, but double-check the pin mapping. The Nano’s pinout is: pin 1 (VDD_3V3), pin 2 (VDD_1V8), pin 3 (DSI_D0_N), pin 4 (DSI_D0_P), pin 5 (GND), pin 6 (DSI_D1_N), pin 7 (DSI_D1_P), pin 8 (GND), pin 9 (DSI_CLK_N), pin 10 (DSI_CLK_P), pin 11 (GND), pin 12 (DSI_D2_N), pin 13 (DSI_D2_P), pin 14 (GND), pin 15 (DSI_D3_N), pin 16 (DSI_D3_P), pin 17 (GND), pin 18 (DSI_GPIO0), pin 19 (DSI_GPIO1), and pin 20 (GND). But the Nano’s connector is only 15 pins, so it uses pins 1-15, with D0, D1, CLK, D2, and D3. The adapter’s 30-pin connector often has additional pins for backlight control, touch, and power. Match the data lanes exactly: D0+ to D0+, D0- to D0-, and so on. A wrong connection can damage the Nano’s DSI controller, which operates at 1.2V for the data lines.

After wiring, you need to modify the Jetson Nano’s device tree to enable the MIPI DSI interface and configure the display parameters. The default kernel (L4T 32.x) has a device tree for the official 7-inch display, but for a generic panel, you’ll need to create a custom overlay. The adapter’s bridge chip requires I2C configuration to set the video timings. For example, the LT8918 uses I2C address 0x48 on the Nano’s I2C bus (usually I2C-1 on pins 27 and 28). You can probe the I2C bus with `i2cdetect -y -r 1` to confirm the chip is detected. The device tree overlay must define the panel’s resolution, pixel clock, and lane count. For a 1080p60 panel, the pixel clock is about 148.5 MHz, and with 4 lanes, each lane runs at 371.25 MHz (148.5 * 4 / 4, since 4 lanes share the load). The kernel’s MIPI DSI driver (tegra-dsi) expects these values in the device tree node.

Here’s a typical device tree fragment for a 1080p panel with 4 lanes:

dsi_panel: panel@0 {
compatible = “simple-panel-dsi”;
reg = <0>;
dsi,format = ;
dsi,lanes = <4>;
dsi,flags = <(MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_BURST | MIPI_DSI_MODE_LPM)>;
panel-width-mm = <309>;
panel-height-mm = <174>;
status = “okay”;
display-timings {
timing@0 {
clock-frequency = <148500000>;
hactive = <1920>;
vactive = <1080>;
hfront-porch = <88>;
hback-porch = <148>;
hsync-len = <44>;
vfront-porch = <4>;
vback-porch = <36>;
vsync-len = <5>;
};
};
};

Compile this overlay with `dtc -@ -I dts -O dtb -o custom.dtbo custom.dts` and load it with `sudo tegra-capture-overlay custom.dtbo`. Then reboot. The display should show the console or desktop. If it doesn’t, check the backlight enable pin. Many adapters have a backlight enable pin that needs to be pulled high. On the Nano, you can use GPIO 17 (pin 11) or GPIO 18 (pin 12) to control it. Add a GPIO backlight node in the device tree: backlight: backlight {
compatible = “gpio-backlight”;
gpios = <&gpio 17 0>;
default-on;
};

Power sequencing is critical. The adapter’s bridge chip must be powered before the MIPI DSI interface is enabled. The Nano’s bootloader initializes the DSI controller early, so if the adapter isn’t powered, the DSI lines may be left floating, causing a lockup. Use a relay or a MOSFET to switch the adapter’s power based on the Nano’s 3.3V rail. For example, connect the adapter’s power enable to the Nano’s 3.3V pin (pin 1) through a 10k resistor. The adapter’s power supply should be stable to within 5% because the bridge chip’s PLL is sensitive to ripple. A 470 µF capacitor on the adapter’s input helps filter noise.

Test the display with a known working panel first. The adapter’s output is compatible with many 4-lane MIPI DSI panels, like those from Innolux or BOE, but check the panel’s datasheet for the exact timing. Some panels require a specific initialization sequence via DCS commands. The adapter’s bridge chip can pass these commands through the I2C bus. For example, the LT8918 has a register map that allows you to set the video mode, lane polarity, and clock polarity. Use `i2cset` to write the values. A common sequence for a 1080p panel is:

i2cset -y -f 1 0x48 0x0A 0x80 (reset chip)
i2cset -y -f 1 0x48 0x0B 0x04 (set 4 lanes)
i2cset -y -f 1 0x48 0x0C 0x00 (disable clock inversion)
i2cset -y -f 1 0x48 0x0D 0x01 (enable video mode)

Then set the video timings in registers 0x10 to 0x1F. The exact values depend on the panel’s datasheet. For a 1920x1080 panel, the horizontal total is 2200 (hactive + hfront-porch + hsync-len + hback-porch = 1920 + 88 + 44 + 148 = 2200). The vertical total is 1125 (1080 + 4 + 5 + 36 = 1125). Write these as 16-bit values in little-endian format. For example, register 0x10 is the horizontal total low byte, 0x11 is the high byte. 2200 decimal is 0x0898, so write 0x98 to 0x10 and 0x08 to 0x11.

If the display shows garbled output, the lane polarity might be wrong. The adapter’s datasheet usually specifies whether the DSI lanes are normal or swapped. The Nano’s DSI controller can invert the polarity with a device tree property: nvidia,dsi-lane-polarity = <0x1F>; where each bit represents a lane (bit 0 for D0, bit 1 for D1, etc.). A value of 0x1F inverts all lanes. Try 0x00 first, then 0x1F if the image is inverted.

Another common issue is the pixel clock mismatch. The Nano’s DSI controller uses a PLL to generate the clock from the system clock. The default PLL rate is 594 MHz for the 7-inch display, but for 1080p60, you need a pixel clock of 148.5 MHz. The PLL must be set to a multiple of this. In the device tree, set nvidia,dsi-pll-rate = <594000000>; and then divide by 4 for 4 lanes (594/4 = 148.5). If the PLL isn’t locked, the display will flicker. Check the kernel log with `dmesg | grep dsi` for errors like “PLL not locked” or “timeout waiting for DSI ready”.

For the Jetson Nano’s software, you need the L4T driver package with the display subsystem. The default image includes the nvdisp driver, but it only supports the HDMI output. For MIPI DSI, you need to load the tegra-dsi module. In the kernel config, ensure CONFIG_DRM_TEGRA_DSI is set to y. On the stock L4T, it’s built as a module, so you can load it with `modprobe tegra-dsi`. Then the display should appear as /dev/fb1. Use `cat /sys/class/graphics/fb1/modes` to see the supported modes. If it’s blank, the mode might not be set. Use `fbset -fb /dev/fb1 -xres 1920 -yres 1080 -vxres 1920 -vyres 1080 -depth 32` to set the framebuffer size.

Power consumption is another factor. The Jetson Nano’s 5V rail can supply up to 2.5A, but the adapter and panel can draw 1.5A to 2A. If you’re using a USB-C power supply, it might not deliver enough current. A 5V/4A supply is recommended for the Nano plus the adapter. Measure the current with a USB meter. The LT8918 chip itself draws about 150 mA, and the panel’s backlight can draw 500 mA to 1A depending on brightness. Use a PWM pin to control the backlight brightness. The Nano’s GPIO 18 (pin 12) can be used as a PWM output. Add a device tree node for PWM backlight: pwm-backlight {
compatible = “pwm-backlight”;
pwms = <&pwm 0 1000000>;
brightness-levels = <0 50 100 150 200 255>;
default-brightness-level = <4>;
};

Finally, test with a simple X11 or Wayland session. The Jetson Nano’s desktop uses Xorg with the nvidia driver. The MIPI DSI display will appear as a second monitor. You can clone the HDMI output to the MIPI display using `xrandr --output DSI-1 --same-as HDMI-0`. But the MIPI display’s refresh rate might be limited by the adapter’s bridge chip. The LT8918 supports up to 60 Hz, but some adapters are limited to 30 Hz for 1080p. Check the datasheet for the actual capability. If the display is too slow, reduce the resolution to 720p. The device tree can be changed to 1280x720 with a pixel clock of 74.25 MHz.

For troubleshooting, use a logic analyzer to probe the MIPI DSI lanes. The differential signals should be 200 mV peak-to-peak. If the signal is too low, the cable might be too long. Keep the FPC cable under 10 cm to avoid signal degradation. The adapter’s input HDMI cable should be shielded, and the power supply should be close to the adapter to reduce voltage drop. Some adapters have a jumper to select the I2C address or the lane count. Set it to 4 lanes and the correct I2C address (0x48 or 0x4C).

One more detail: the Jetson Nano’s MIPI DSI interface is designed for the official display, which has a resolution of 1024x600. For higher resolutions, the DSI controller’s FIFO might overflow if the pixel clock is too high. The Nano’s DSI controller has a 4KB FIFO, and at 1080p60, each line is 1920 pixels * 3 bytes = 5760 bytes, which exceeds the FIFO. The controller uses a burst mode to send data in chunks, but if the adapter’s bridge chip can’t handle the burst, you’ll see tearing. The LT8918 has a built-in buffer of 2 lines, so it can handle 1080p60. But if you use a different bridge chip, check its buffer size.

In summary, the key steps are: power the adapter separately, map the FPC pins correctly, configure the device tree with the exact timings, set the I2C registers for the bridge chip, and adjust the kernel modules. Each step requires careful measurement and testing. The adapter’s quality varies, so buy from a reputable supplier like the one linked above. The hdmi to 4 lane mipi dsi adapter from DisplayModule is tested with the Jetson Nano and includes a 30-pin to 15-pin cable, making the connection easier. It supports 1080p60 and has a built-in backlight driver. The datasheet includes the I2C register map and device tree example, which saves time. Always start with a low resolution like 800x480 to verify the connection, then scale up. The Nano’s GPIO pins can be used to toggle the display power and backlight, but avoid using the 5V pin for the adapter’s power to prevent brownouts. Use a separate 5V supply with a common ground. The total system current should be under 3A for reliable operation.