Re: [PATCH v2 1/1] xhci: add USB2 test mode support

From: Mathias Nyman
Date: Wed Feb 08 2017 - 09:17:10 EST

On 08.02.2017 15:44, Alexander Stein wrote:
This patch adds support for USB2 test mode (Test_J, Test_K,
Test_SE0_NAK and Test_Packet) per XHCI spec 4.19.6.

USB2 test mode is a required hardware feature for system integrators
validating their hardware according to USB spec, regarding signal
strength and stuff. It is purely a hardware test feature.

Usually you need an oscilloscope and have to enable those test modes on
the hardware. This will send some specific test patterns on D+/D-. There
is no report available (in Linux itself) as it is purely externally
visible. Regular USB usage is not possible at that time.
Anyone (well access to e.g. /dev/bus/usb/001/001 provided) can use it by
sending appropriate USB_PORT_FEAT_TEST requests to the hub.
The same feature for ehci based hosts is already available at

Signed-off-by: "Wang, Yu" <>
Signed-off-by: "Li, Guanglei" <>
Signed-off-by: "Wu, Hao" <hao.wu@xxxxxxxxx>
Signed-off-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxxxxxxxx>

I think there's a reworked series of this feature already posted at:

But this change log is now better
I was thinking about adding that to 4.12