On Mon, 23 May 2011, Tanya Brokhman wrote: > I ran some more tests with xhci and I think (or hope :) ) I figured this > out: > When connecting a gadget driver that is marked as SS device (the flag > CONFIG_USB_GADGET_IS_SUPER_SPEED = true) to a SS port over SS cable - > the enumeration fails if that gadget driver doesn't provide SS descriptors. > BUT: if I connect the same device via HS cable to SS port - the enumeration > is successful. I think that this is the case where xhci-ring handles the > device over to the HS hcd :) (By the way, I think that in xhci the > shared_hcd is SS and the main_hcd is HS) > > In conclusion it seems to me that the device speed is determined by 2 > things: > 1. the cable used > 2. whether the device HW supports SS protocol. In our scenario it can since > SS support is enabled in our udc. (We haven't released it yet.) > So when a HS device is connected to a SS port, the xHCI checks it's speed > and if necessary handles it over to the SS root hub. But this is done prior > to the enumeration phase so if the device speed is SS but it has no SS > descriptors - the enumeration will fail. The enumeration itself occurs not > in xhci but in hub.c so the xhci isn't aware of the fact that it failed and > doesn't handle this. > > Since in dummy_hcd all of this is much simpler I think that the device speed > should be determined by driver->speed and "which type of cable the > connection was made over - SS or HS". The "cable type" is exactly what the > module parameter is. > > My familiarity with the Linux host isn't as good as I would like it to be > (still working on that) so I might be wrong with my conclusions... Your analysis is basically correct. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
