On Tue, 31 Mar 2015, Rong Wang wrote: > Hi all, > > I'm on USB certification of a vendor SoC, and there's a case called > "Bus powered hub power exceeded test" in the compliance plan defined > by the usb.org. It requires an error message when a device (Max power > descriptor >100mA) is attached to an external bus powered hub. > > But when I attached the bus powered hub to Linux (Ubuntu 14.04), I > found that it always reported as self powered ... > The hub->mA_per_port is always set as full_load (500mA for usb 2.0 > hub) since reported as self powered hub. > So when I attach a usb device with ( 100mA < Max power descriptor <= > 500mA), linux won't show error messages. > > I'm wondering why the bus powered hub reported as self powered? And is > any switch to make it bus powered? The reason is simple: The hub is buggy. It tells the computer that it is self-powered even though it isn't. No, there is no switch to fix it. 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
