Uno Q USB port not working if board powered from 5V

ptillisch · May 1, 2026, 7:37am

In order to make all relevant information available to interested parties, I'll share a link to the related GitHub issue:

github.com/arduino/linux-qcom

[BUG] USB Host Mode not working when powered via VIN - workaround available

opened 09:24AM - 11 Dec 25 UTC

Psalmustrack

## Description When the Arduino UNO Q is powered via VIN pins (7-24V) instead o…f USB-C, the USB-C port does not function in host mode. USB devices (Zigbee dongles, keyboards, cameras, etc.) are not recognized. ## Steps to Reproduce 1. Power Arduino UNO Q via VIN (12V) and GND pins 2. Connect a USB device via USB-C to USB-A adapter 3. Run `lsusb` - no devices shown 4. Check `cat /sys/class/typec/port0/data_role` - shows `host [device]` (device mode active) ## Expected Behavior USB-C port should function in host mode when powered via VIN, recognizing connected USB devices. ## Actual Behavior The DWC3 USB controller defaults to "device" mode because no USB-C CC line negotiation occurs at boot. The sysfs file `/sys/class/typec/port0/data_role` is read-only, preventing runtime role switching via standard methods. ## Root Cause When booting via VIN power without a USB-C cable connected: 1. PM4125 Type-C controller detects nothing on CC pins 2. UCSI framework doesn't send host role notification 3. dwc3-qcom driver defaults to device mode ## Workaround Writing to debugfs forces host mode: ```bash echo host > /sys/kernel/debug/usb/4e00000.usb/mode ``` I've created a systemd service that applies this fix automatically at boot: 👉 https://github.com/Psalmustrack/arduino-uno-q-usb-fix ## Proposed Fix Consider one of these solutions for future OS releases: 1. **Device tree modification** - Set `role-switch-default-mode = "host"` or `dr_mode = "host"` 2. **Make data_role writable** - Enable runtime role switching via `/sys/class/typec/port0/data_role` 3. **Boot service** - Include a systemd service that forces host mode when VIN power is detected ## Environment - **Board:** Arduino UNO Q (2GB RAM / 16GB eMMC) - **OS:** Debian Linux (stock image) - **Kernel:** 6.16.0-geffa8626771a ## Related Discussions - https://forum.arduino.cc/t/usb-power-disabled-if-using-vin-power-pin/1411831 - https://forum.arduino.cc/t/uno-q-usbc-dongle-issue/1410296 - https://forum.arduino.cc/t/connecting-usb-camera-to-uno-q/1412062 ## Additional Context Arduino staff acknowledged this limitation but classified it as "not a supported scenario". However, many users need VIN power for robotics, home automation (Home Assistant), and embedded projects where USB-C power is not practical. The workaround has been tested successfully with: - Sonoff Zigbee 3.0 USB Dongle Plus - USB cameras - USB keyboards/mice via hub

There is associated discussion here:

Topic		Replies	Views
UNO Q, USBC dongle issue UNO Q	29	2306	March 27, 2026
UNO Q: USB Power disabled, if using VIN Power pin UNO Q	20	692	February 24, 2026
UNO Q: What is wrong with my UNO Q board? UNO Q	33	428	May 19, 2026
Connecting USB Camera to Uno Q UNO Q	23	2189	February 15, 2026
Fail at the first hurdle UNO Q	148	3539	November 25, 2025

Uno Q USB port not working if board powered from 5V

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