On Tue, 26 Jul 2011, Oliver Neukum wrote: > Am Dienstag, 26. Juli 2011, 16:16:28 schrieb Alan Stern: > > > I am afraid this is a true problem. We need to make the computation of > > > the available power dynamic. The computation of hub->mA_per_port > > > once is insufficient, as we cannot say that a limit valid for any port is valid > > > for every port forever. > > > > You have misunderstood the purpose of hub->mA_per_port. It is not a > > dynamic value reflecting the amount of current available at any moment. > > Rather, it is a static upper limit reflecting the computations > > prescribed by the USB-2.0 spec, section 7.2.1. > > The problem here is that the host violates the requirements of the section. > It cannot supply both ports at the same time with enough power. We could > ignore that issue. But if we don't, I think we need to go dynamic. We already log a warning message if an external hub can't supply sufficient power to all its ports. We could do the same for root hubs. We could even log a warning message if a config change would cause the parent hub to exceed its power budget. Beyond that, I don't see what else can be done. 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
