Dock USB C and External Displays

Dock, USB-C, power delivery, and external displays

A dock is several paths in one enclosure: USB hub/controller, USB Ethernet/audio/storage, USB-C Power Delivery, DisplayPort Alt Mode, and an HDMI/DisplayPort converter. One can fail while the others work. DeckDoc can judge exported behavior and correlation; it cannot certify the dock's power rails or signal integrity electrically.

Capture two controlled states

Run one report with the symptom present while docked:

sudo ./deckdoc.sh

Then change only the path under test and run a second report—for example official/known-good charger direct to Deck, direct USB-C display, another cable, or another Ethernet adapter. Record dock model, power supply, cable, display/input/mode, peripherals, exact failure time, and what remained functional.

Read module_dock.log, module_display.log, module_battery.log, module_acpi.log, and the probe incident if present.

What module_dock.log sees

• USB topology and vendor/product IDs, with serial numbers intentionally omitted;
• Type-C data/power role, orientation, partner presence, PD and Type-C revision when exported;
• DisplayPort Alt Mode configuration/pin/HPD when the driver exports it;
• USB/PD supply voltage, current, power, online state, and a clearly labeled instantaneous calculation;
• external DRM connector, EDID byte count, link state, and modes;
• likely USB Ethernet interface, driver, carrier, speed, and state;
• current-boot xHCI, UCSI, Type-C, USB over-current, reset/disconnect, and display-link errors.

The kernel Type-C class defines role, partner, power_operation_mode, PD revision, and Alternate Mode exports, but drivers are not required to expose every field. “Not exported” is not a zero-voltage or bad-dock diagnosis. See the Linux Type-C class and Type-C sysfs ABI.

Decision boundaries

Observation	Stronger next branch
Direct charger works; docked charging repeatedly renegotiates or drops	dock PSU, cable, PD passthrough, dock controller
Direct USB-C display works; same display/cable path through dock fails	dock/adapter conversion path
Dock works on another host	Deck port, SteamOS driver, mode, or Deck/dock combination
Multiple hosts fail on the same dock/cable/display	shared dock/cable/display path
Whole USB hub, Ethernet, and display reset together	controller, upstream cable, or power path before one peripheral
One peripheral resets while the rest remain stable	that device, its downstream port/cable, or its driver
External display fails but USB/Ethernet/charging remain stable	Alt Mode, converter, EDID/mode/link path
Failures reproduce only after suspend	resume/reinitialization path; correlate PM timestamps

A DOCK_SIGNATURE: TOPOLOGY_CHANGE_WITH_DOCK_PATH_ERROR means a reset/disconnect and a selected host/PD/display-link error both exist in the boot. It does not prove the dock caused either record; timestamps and the direct-vs-dock comparison decide whether the signature is relevant.

Voltage and power limits

When voltage/current are exported, DeckDoc reports raw micro-unit values and calculated instantaneous watts. Battery current may differ from negotiated adapter power because the running Deck consumes power, conversion has losses, and the battery may charge or discharge. Many docks expose no rail telemetry. Software output is not an oscilloscope, USB-PD analyzer, or load tester.

Stop using a dock/cable for sparking, electrical smell, abnormal connector heat, visible damage, over-current logs, or repeated power loss. Do not stress-test it further.

Valve's docking guide is the primary source for supported reset and cable/display cross-tests. Do not flash unofficial dock firmware, force unsupported timings, unbind the USB host controller remotely, or backfeed through a powered hub.