On Thu, Apr 2, 2015 at 11:48 AM, Peter Chen <Peter.Chen@xxxxxxxxxxxxx> wrote: > >> Yes >> >> >> reported as self powered, per port power limit is 500 mA, so the >> >> device may be configured and maybe work normal. >> >> >> > >> > I see your hub report its max power is 100 mA, so if it can report as >> > self powered, then the hub's behavior is correct, and will not be >> > rejected by kernel. And you should get an error message when the >> > device which declares its max power larger than 100mA plugs in hub's port, >> right? >> >> The external hub could be enumerated regardless of it's reported to linux as >> self-powered or bus-powered. >> The difference is that when it's reported as self-powered / bus-powered, >> driver will set the per port power limit to 500 mA / 100 mA. When a usb device >> is attached to one port of the hub, driver will compare the MaxPower of the >> configuration of the device with the hub port power limit, if the MaxPower is >> greater than the port power limit, the configuration will be rejected. >> >> >> 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? >> >> > > So, the current hub code is correct, the Lab will use the well-behavior hub, it should > no problem for this test item, right? I wrote a mail to the lab for the power info of the hub they will apply in the certification test. I assume they will use a true bus-powered hub. Regards Rong -- 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
