The Lontium LT8912B MIPI-to-HDMI bridge converts the STM32MP25 MIPI DSI signal to one suitable for HDMI displays.

HDMI is the default configuration for ConnectCore MP25 Development Kit.

Kernel configuration

You can manage the LT8912B support through the following kernel configuration option:

  • Lontium LT8912B MIPI-DSI to LVDS and HDMI/MHL bridge (CONFIG_DRM_LONTIUM_LT8912)

This option is enabled as built-in on the default ConnectCore MP25 kernel configuration file.

Kernel driver

The driver for the LT8912B bridge is located at:

File Description

drivers/gpu/drm/bridge/lt8912.c

LT8912B MIPI-to-HDMI bridge driver

Device tree bindings and customization

The LT8912B bridge is documented at Documentation/devicetree/bindings/display/bridge/lontium,lt8912.txt. The LT8912B bridge is defined in the ConnectCore MP25 Development Kit device tree file.

Definition of the LT8912B

ConnectCore MP25 Development Kit device tree
&i2c2 {
...

	lt_bridge: lt8912@48 {
		compatible = "lontium,lt8912";
		reg = <0x48>;
		reset-gpios = <&gpiod 4 GPIO_ACTIVE_LOW>;
		hpd-gpios = <&gpiod 2 GPIO_ACTIVE_HIGH>;
		no-edid;
		digi,dsi-lanes = <4>;
		status = "okay";

		port {
			lt8912_1_in: endpoint {
				/* add lanes */
				remote-endpoint = <&dsi_out>;
			};
		};
	};
};

...

&dsi {
	#address-cells = <1>;
	#size-cells = <0>;
	status = "okay";

	ports {
		#address-cells = <1>;
		#size-cells = <0>;

		port@0 {
			reg = <0>;
			dsi_in: endpoint {
				remote-endpoint = <&ltdc_ep0_out>;
			};
		};

		port@1 {
			reg = <1>;
			dsi_out: endpoint {
				remote-endpoint = <&lt8912_1_in>;
			};
		};
	};
};