On Sat, 07 November 2009 Oliver Neukum <oliver@xxxxxxxxxx> wrote: > Am Samstag, 7. November 2009 18:06:05 schrieb Bruno Prémont: > > > When a hub is bus-powered, the USB specification does not allow > > > it to provide more than 100 mA to each port. Since the Sandisk > > > pen wants more than 100 mA, the kernel rejects its configuration. > > > You can override this decision if you want by writing the > > > appropriate config value to the > > > pen's /sys/bus/usb/devices/.../bConfigurationValue file. > > > > That's a not so nice limitation of the spec... It would have been > > more useful if the "available" power could be forwarded to a single > > port of the HUB even if in that case 0ma remain for the other 3 > > ports. > > Suppose we did this and somebody plugs in another device. > Do we refuse to service this device? I would say yes as there is not enough power left in the budget, first-come first-served would then apply. There are also HUBs with more than 4 ports (though they might refuse to work bus-powered), in this case with 100ma per port the same result would be achieved with plugging in the fifth 100ma device. Bruno -- 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
