On Fri, 3 Aug 2012, Sarah Sharp wrote: > On Thu, Jul 19, 2012 at 10:42:23AM -0400, Alan Stern wrote: > > The same is true for external ports if they are marked as > > non-removable. For example, consider a compound keyboard/mouse device > > with a built-in hub. The connections from the keyboard and the mouse > > to the hub are internal and not removable. > > Alan, is there a way to know whether a hub is part of a compound device > by looking at the device descriptors? No. > Also, what do you propose we do with empty ports on the built-in hub? I > know some keyboards expose those extra ports on the outside of the > keyboard, but others may have internal unconnectable ports. I think the > safest thing to do is leave ports on built-in hubs powered on, since we > can't get any ACPI information for them. Right. In the absence of ACPI information, we should leave ports powered on. We currently have no other way of knowing whether they are unconnectable. > Further, do devices like BMCs look like a compound device? I know some > of them will disconnect the storage or CD drives when they're not being > used, which may break your assumption that devices behind a hub in a > compound device cannot be disconnected. That's a good point. Even though the connection may be physically permanent, the device may disconnect itself from the bus from time to time. But it's not all that bad; if we miss a disconnect/reconnect sequence because the port happened to be powered down at the time, it doesn't matter since the same device will still be attached. 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
