DESK-MX8M-L-TN-0003: HDMI output on MITO8M Mini

History
Issue Date	Notes
2024/05/30	DESK-MX8M-L-4.1.0 release

Introduction

Using a standard HDMI panel can easily simplify a product design. This allows to avoid the usage of a particular LCD panel and the related mechanical and electrical adaptations.

This Technical Note (TN) describe how to configure the video signal chain for using an HDMI panel along the MITO 8M Mini Evaluation Kit. The standard Weston desktop will be available on the LCD panel. More technical information about the DRM chain can be found in the drm bridge chaining blog post of 3mdeb.

Testbed

A bootable microSD card associated with the release 4.1.0 of the DESK-MX8M-L kit can be used for this purposes. In this Technical Note the dave-image-devel-desk-mx8mm SD card image is used.

From the hardware point of view, the MITO 8M Mini Evaluation Kit contains the following items:

• SBCX with MITO 8M Mini SOM
• LVDS to HDMI adapter
• HDMI display 1280x720

which demonstrates the usage of an HDMI panel for an Embedded system.

Software structure

The software (and related hardware) blocks are depicted here below:

MITO 8M Mini SOM LVDS to HDMI block diagram

The picture shows how the video signals are managed:

• the DSI video signals are internally generated by the SoC
• in the MITO 8M Mini SOM , these signals are converted to LVDS using a DSI-to-LVDS IC
• the LVDS signals are converted to HDMI using another IC bridge (externally to the SOM, i.e. with an external electronic board)
• finally, the HDMI signals are sent o the HDMI panel

Device-tree configuration

The SN65DSI84 mipi to LVDS bridge is configured in the device tree in the following way:

mipi_to_lvds: sn65dsi84@2c {
    compatible = "ti,sn65dsi83";
    reg = <0x2c>;
    enable-gpios = <&gpio1 6 GPIO_ACTIVE_HIGH>;
    interrupts-extended = <&gpio1 5 GPIO_ACTIVE_HIGH>;
    clocks = <&mipi_dsi 0>, <&clk IMX8MM_CLK_LCDIF_PIXEL>;
    clock-names = "mipi_clk", "pixel_clock";
    display = <&display_subsystem>;
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_i2c1_sn65dsi84>;
    sync-delay = <512>;
    dsi-lanes = <4>;
    status = "okay";

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

        port@0 {
            reg = <0>;
            lvds_in: endpoint {
                remote-endpoint = <&mipi_out>;
                data-lanes = <1 2 3 4>;
            };
        };

        port@2 {
            reg = <2>;
            lvds_out: endpoint {
                remote-endpoint = <&it6263_in>;
                attach-bridge;
        };
    };
};

to activate the LVDS to HDMI bridge we need to define another node in the device tree:

&i2c3 {
    lvds-to-hdmi-bridge@4c {
        compatible = "ite,it6263";
        reg = <0x4c>;
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_it6263_en>;
        reset-gpios = <&gpio5 2 GPIO_ACTIVE_LOW>;
        status = "okay";

        port {
            it6263_in: endpoint {
                remote-endpoint = <&lvds_out>;
            };
        };
    };

Test on the target

Once the system completed the boot phase, using the modetest command we have the following result:

# modetest
(...)
Connectors:
id      encoder status          name            size (mm)       modes   encoders
35      34      connected       HDMI-A-1        340x190         2       34
  modes:
        index name refresh (Hz) hdisp hss hse htot vdisp vss vse vtot
  #0 1280x720 60.00 1280 1390 1430 1650 720 725 730 750 74250 flags: phsync, pvsync; type: driver
  #1 1280x720 50.00 1280 1720 1760 1980 720 725 730 750 74250 flags: phsync, pvsync; type: driver
(...)
CRTCs:
id      fb      pos     size
33      40      (0,0)   (1280x720)
  #0 1280x720 60.00 1280 1390 1430 1650 720 725 730 750 74250 flags: phsync, pvsync; type: driver
(...)

so the HDMI output has been properly configured.

On the HDMI panel we can see the Wayland/Weston desktop

Weston desktop on MITO 8M Mini Evaluation Kit