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USB 3.0 Diagnostics and FAQ

  • U2 works but U3 does not: inspect SuperSpeed TX/RX pairs, orientation mux, ComboPHY selection, reference clock, and equalization.
  • dwc3_sunxi_plat fails to load: inspect DWC3, PHY, reset, clock, power domain, and parent/child node status.
  • xHCI registration fails: inspect resource conflicts, PHY readiness, and dr_mode.
  • ADB or Mass Storage is not SuperSpeed: inspect Gadget descriptors, maximum-speed, and whether the selected function supports SuperSpeed.
  • MTP stalls or throughput is low: inspect link speed, filesystem, PC driver, and CPU/memory bottlenecks.
dmesg | grep -Ei 'dwc3|xhci|typec|combophy|superspeed'
find /sys/kernel/debug -iname '*dwc3*' -o -iname '*xhci*'
cat /sys/class/udc/*/state 2>/dev/null

General diagnostic order​

  1. Schematic and power.
  2. Node and pinctrl in the final DTB.
  3. Final .config and modules.
  4. Probe, clock, reset, and IRQ logs.
  5. Device node and sysfs/debugfs.
  6. Minimal functional test.
  7. Stress, suspend, and abnormal hot-plug tests.

Do not treat the removal of an error log as a fix. Find the first failure and validate its upstream and downstream dependencies.