On Mon, November 23, 2015 2:43 am, Alan Stern wrote: > On Sun, 22 Nov 2015, Patrick Shirkey wrote: > >> > It _is_ possible to disable xHCI at the system level. By sending the >> > proper command to the appropriate sysfs file, you can unbind the >> > xhci-hcd driver from the xHCI controller. This will disable the >> > controller, and so all further USB communications will run no faster >> > than High Speed. (Or if your computer doesn't have an EHCI >> controller, >> > you won't get any further USB communications at all.) >> > >> >> Is there a method to determine if the system has multiple or single >> controllers available? > > lspci will tell you. > >> Do you or anyone else here have a link to the sysfs command to unbind >> the >> controller? > > If you provide the output from "lspci", I will tell you what command to > use. > Here's the USB info from lspci. # lspci 00:14.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB xHCI (rev 05) 00:16.0 Communication controller: Intel Corporation 8 Series/C220 Series Chipset Family MEI Controller #1 (rev 04) 00:1a.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB EHCI #2 (rev 05) 00:1d.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB EHCI #1 (rev 05) >> > Actually it's a little more complicated than that. Some systems have >> a >> > software-settable switch that determines whether devices will connect >> > to the xHCI or the EHCI controller. On such systems, Linux sets the >> > switch to use xHCI, unless the kernel was built without xHCI support. >> > Therefore, although it is possible to force the use of EHCI on such >> > systems, in order to do so you have to rebuild the kernel. >> > >> >> >> In regards to the last item can you provide some more details on why the >> software switch is only set if the kernel module is enable/disabled? >> >> I assume it has something to do with compiler flags and run time >> efficiency? > > No, it's simpler than that. If the kernel is built without support for > xHCI, it would be foolish to connect devices to the xHCI controller -- > then the system wouldn't be able to communicate with them! > > Conversely, if the kernel does have support for xHCI, we assume that > the user will prefer xHCI over EHCI if the motherboard has xHCI. > Therefore the switch does get set to connect devices to the xHCI > controller. > Obviously the solution above should suffice for my purposes but out of interest is it viable to make the switch accessible to run time configuration? -- Patrick Shirkey Boost Hardware Ltd -- 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
