On Sun, 20 Dec 2009, John Lane wrote: > Good afternoon, this is my first post here. I have tried in vain to get > answers elsewhere so I hope you can help me. > > I would like to know the correct way to override USB power budgets. > > I have a device that reports that it requires 510 mA. I've read that > this number is reported because it is what 255 represents and the device > designer probably thought they could get away with setting the maximum > 8-bit value into "MaxPower". Obviously now that power requirements are > checked, they can't. > > This does not help me - I have a device that was working just fine but > ceased working after a kernel update. > > I have read that power checking can be overriden by writing a 1 to the > file /sys/bus/usb/devices/2-6.1.3/bConfigurationValue. This doesn't > work: it just increases the allowance to 500ma which still falls short > by 10ma. On the contrary; it does work. And it doesn't increase power allowances -- it goes ahead and violates the power budget. > My /var/log/messages upon plugging in the device > > Dec 20 14:19:51 tma1 kernel: [192154.688351] usb 2-6.1.3: new full speed > USB device using ehci_hcd and address 28 > Dec 20 14:19:51 tma1 kernel: [192154.803529] usb 2-6.1.3: rejected 1 > configuration due to insufficient available bus power > Dec 20 14:19:51 tma1 kernel: [192154.803532] usb 2-6.1.3: no > configuration chosen from 1 choice > > And after setting bConfigurationValue: > > root:~# echo -n 1 >/sys/bus/usb/devices/2-6.1.3/bConfigurationValue > Dec 20 14:20:53 tma1 kernel: [192216.854959] usb 2-6.1.3: new config #1 > exceeds power limit by 10mA That message is merely a warning. The configuration was installed anyway. > I would like to know how to completely override this checking, or how to > supply another configuration choice that I can configure to allow 510ma. You override it by writing to bConfigurationValue, just as you were doing. 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
