Dennis HilkLinux diagnosticsDE

Bluetooth

Bluetooth H4 UART transport context

A serial HCI transport context for an embedded Bluetooth controller. A UART-connected controller can exist without appearing in lspci or lsusb.

Editorial source review: Share public profileOpen in the identification tool
On this page
  1. Overview & identity
  2. Driver & binding
  3. Firmware
  4. Read-only diagnostics
  5. Limitations & related issues
  6. References

Overview & identity

H4 is a UART protocol, not a vendor/device identity. This profile is secondary context only; the hci_uart module alone cannot determine the selected protocol or chipset.

This is an explicit class, transport or driver-context profile. It is not an exact numeric product match.

A numeric match establishes a candidate family within the reviewed evidence. Marketing names, board variants, subsystem conditions and successful operation remain separate questions.

Driver & binding

The source includes H4 in hci_uart when the protocol option is configured. Board description or an existing serial attachment determines which device reaches this path.

  • hci_uart — kernel driver/module candidate

Detected, bound, operational: learn the difference

Firmware

Device/revision dependent

H4 framing does not define a chipset firmware filename. A vendor setup path may still require firmware.

Inspect firmware packaging on your distribution

Read-only diagnostics

Run one displayed command at a time. Replace uppercase placeholders with the affected device, interface or module from your own output. Commands are never executed here. Read-only output can still contain private identifiers.

Read the controller parent path

readlink -f /sys/class/bluetooth/CONTROLLER/device

Replace CONTROLLER with the local hci name, such as hci0, found in /sys/class/bluetooth. The path helps distinguish USB, serial and SDIO parents. It does not prove which UART protocol is active. No root privileges are needed.

Read controllers visible to BlueZ

bluetoothctl list

This asks the BlueZ daemon for known controllers without discovery or pairing. An empty response can mean daemon or D-Bus access problems as well as absent controllers; compare kernel enumeration. Normally no root privileges are needed.

Read controller initialization

journalctl -k -b --no-pager

Read the current boot’s kernel messages for the controller, requested firmware and setup result. Journal visibility depends on local permissions; an unreadable log is not evidence of no errors. This command does not change the device.

Limitations & related issues

A serial port or loaded module is not proof of a Bluetooth controller. Clock, reset, power resources and any vendor initialization are board-specific and not inferred here.

These guides are linked for relevant observations, not as known defects of every device in this family.

Choose a hardware diagnostic workflow · Inspect a log excerpt in Fix Lab

References

Source review records a checked implementation or document, not a reproduced hardware test. Version-specific tables do not establish a minimum kernel or guaranteed operation.