On Tue, Feb 10, 2015 at 09:58:23PM +0800, Huang Rui wrote: > On Mon, Feb 09, 2015 at 08:59:06PM -0500, Alan Stern wrote: > > On Tue, 10 Feb 2015, Huang Rui wrote: > > > > > On Mon, Feb 09, 2015 at 10:59:42AM -0500, Alan Stern wrote: > > > > On Mon, 9 Feb 2015, Huang Rui wrote: > > > > > > > > > Hi, > > > > > > > > > > Do you have any trick to downgrade one USB3 capacity device from super > > > > > speed mode to high speed mode on xhci port via host side? > > > > > > > > Connect it to the host by a USB-2 cable. > > > > > > > > > > If physical connection and port number are fixed, any idea on software > > > side? > > > > It may be possible to do this by disabling the port in some way (put it > > in some appropriate link state -- I don't know which one). When the > > device sees the SuperSpeed connection is gone, it should reconnect at > > high speed. > > > > You mean I should set link status of the special port on SS.Disabled > state, not let it into Rx.Detect statue, right? Then the link can not > go to Polling, and the device aborts this port and reconnect to the > USB2 roothub port, is that right? We got you covered. Look at dwc3's binding document and grep drivers/usb/dwc3 for maximum_speed. You can pass your desired maximum speed via platform_data or DT. Note that the driver will ignore that maximum_speed argument if you're dealing with a known-broken of the IP (also comments added in source code to describe the problem). cheers -- balbi
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