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    # Enable eDP Hotplug with 6ms pulse
    register "gpu_dp_d_hotplug" = "0x06"

    # Enable DDI1 Hotplug with 6ms pulse
    register "gpu_dp_b_hotplug" = "0x06"

    # Enable DDI2 Hotplug with 6ms pulse
    register "gpu_dp_c_hotplug" = "0x06"

    # Set backlight PWM values for eDP
    register "gpu_cpu_backlight" = "0x00000200"
    register "gpu_pch_backlight" = "0x04000200"

    # Enable Panel and configure power delays
    register "gpu_panel_port_select" = "1"            # eDP
    register "gpu_panel_power_cycle_delay" = "6"        # 500ms
    register "gpu_panel_power_up_delay" = "2000"        # 200ms
    register "gpu_panel_power_down_delay" = "500"        # 50ms
    register "gpu_panel_power_backlight_on_delay" = "2000"    # 200ms
    register "gpu_panel_power_backlight_off_delay" = "2000"    # 200ms
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I assume SOC has 3 display port, called eDP, DDI1 and DDI2.
The code above enable eDP only. How are the DDI1 and DDI2 enabled?