On Fri, 23 Sep 2011, Steve Calfee wrote: > On 09/23/11 07:27, Alan Stern wrote: > > On Thu, 22 Sep 2011, Iain Barker wrote: > > > >> Hi all, > >> > >> Is it possible to limit the maximum speed at which a USB 2.0 HUB will connect to USB devices? > >> e.g. to make USB 2 devices connect at FULL_SPEED instead of HIGH_SPEED > > > > The only way to do this is to force the hub itself to connect at full > > speed. There's no way to tell a hub to degrade just one of its ports. > > If the hub is plugged directly into an EHCI controller and there's no > > companion USB-1.1 controller (as is the case with Intel's > > "rate-matching" hubs), there's no way to do it at all. > > > Hi Iain and Alan, > > Yes, there is a way to do it. Connect a FS only hub in front of the one > you want to downshift. That will shift the entire downstream bus to FS only. That's what I said above: Force the hub itself to connect at full speed. In this case it's not possible. The hub is built into the system; there's no way to interpose another hub between it and the controller, and even if there were, the EHCI controller wouldn't be able to communicate with a full-speed-only hub. More and more we're seeing systems that have only an EHCI controller with no companion controllers; all communication has to take place through the built-in hub. 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
