I tested it using the bluetooth-next, with HEAD at a3975db95fcd8e304f1ee4b0be1895038942a8ef. It rejects the connection parameter update request at least for the case where the min > max, which is one of the failed conditions for the hci_check_conn_params() Note that TSPX_iut_invalid_connection_interval_{min, max} in the IXIT can be used to create faulty connection parameters. The specific test steps are: 1. Set TSPX_iut_invalid_connection_interval_min to a value larger than TSPX_iut_invalid_connection_interval_max, e.g. 0xAB and 0xAA respectively. 2. Start the GAP/CONN/CPUP/BV-05-C case on PTS. 3. Enter bluetoothctl. Use "scan on" to find the address of PTS dongle. 4. Meanwhile, PTS will ask for connect request. Connect to it by running "connect $PTS_ADDR" in bluetoothctl. 5. At this point the PTS would send the parameter update request with faulty parameters set in the IXIT. Kernel will reject this request. 6. PST will then ask to send a disconnect request. Run "disconnect" in bluetoothctl. The test case should pass after disconnection. Tested-by: Yo-Jung (Leo) Lin <leo.lin@xxxxxxxxxxxxx>