mbed-os/TESTS/usb_device/basic/README.md

Testing the USB device data toggle reset with a Linux host

When you run the tests-usb_device-basic test suite on a Linux machine, please make sure that at least one of the following prerequisites are met:

• using the Linux kernel 4.17 or newer,
• using the eHCI USB driver instead of xHCI.

Implementations of the xHCI driver prior to version 4.17 of the Linux kernel did not have the functionality necessary to test "endpoint test data toggle reset". Even though the data toggle is correctly reset on the device side, the host side will not be synchronized and the test will falsely fail.

Further reading:

1. the Linux kernel patch adding missing xHCI behavior,
2. LKML discussion explaining the details of this issue.