On Tue, 7 Jan 2014, Holger Hans Peter Freyther wrote: > On Mon, Jan 06, 2014 at 04:44:51PM -0500, Alan Stern wrote: > > > Finally, blacklisting xhci-hcd won't solve the problem at hand, because > > the ports get switched from EHCI to xHCI during early PCI processing, > > before xhci-hcd is loaded. The only check is for whether > > CONFIG_USB_XHCI_HCD is enabled, which isn't affected by blacklisting. > > > > As far as I can see, the code that switches the ports back to EHCI gets > > run only when the computer is turned off (and then only for some types > > of machines). > > I think in my case quirk_usb_handoff_xhci is called during boot that > will switch the ports to the XHCI. That's what I said. Early PCI processing occurs during boot. > The question is about defaults. My RFC patch proposed to route the > ports to the EHCI until the XHCI module is loaded. I had modified a > comment to highlight a potential issue with this approach. The comment > mentioned that the code tries to avoid taking away an already enumerated > device (e.g. usb storage already mounted) from the EHCI. Indeed, port switching should be avoided once the USB buses are active. > In my case this did not happen. ehci-hcd starts after xhci-hcd but this > might be sheer luck. The question is if this can be made deterministic > or not. No, it cannot. > > The best way to solve this problem would be a boot command-line option. > > Do you have a proposal for a name? One possibility: noxhci-port-switch 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
