On Wed, 1 Apr 2015, Rong Wang wrote: > Hi Alan, > > Thanks for the confirmative answer, since I suspect it's the bug > of the hub first, but all the three hubs at my hand report the same > status. I have had some hubs that made the same mistake. > I can see why the hubs are reported as self powered, e.g. if there's > a device configured with max power equals to 120 mA, if the hub is > self powered, the configuration will be rejected by kernel. But if it's > reported as self powered, per port power limit is 500 mA, so the > device may be configured and maybe work normal. > > But will it cause a runtime error? Say I have a embeded usb host which > can supply 500 mA at most, when the hub reported as self powered and > attached with two devices both with max power equals to 250 mA. Both > device can be configured, but if they are both working at the most power > requirement at the same time, there should be some power problem, right? Yes indeed, there could be a problem. Most of the time it works out okay, because devices rarely need their peak power requirement. 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
