On Tue, 23 Jun 2009, Mitch Davis wrote: > Hello, > > We have some USB devices attached to an EHCI chip which get themselves > wedged sometimes, and we would like to power cycle them using the > EHCI's ability to control power to the USB device. Is this possible? No. > I found a function in ehci-hcd.c that might do what we want: > > http://lxr.linux.no/linux+v2.6.30/drivers/usb/host/ehci-hcd.c#L408 > > Will that do it? No. The EHCI hardware commonly found in personal computers is not capable of turning off bus power. > Who calls that function, and how can I trigger it? It is called when the driver initializes the EHCI hardware. You cannot trigger it. > I found another message which suggests there's a /sys entry (and > hence, a userspace way) to do it: > > https://lists.linux-foundation.org/pipermail/linux-pm/2005-March/006596.html That message is over 4 years old! Naturally it isn't applicable to the current kernel. > But I can't find these on my machine. Any suggestions on how to get them? The best you can do is plug your device into a hub. Some hubs are capable of port power control, others aren't. Check out this web page: http://www.gniibe.org/ac-power-by-usb/ac-power-control.html 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
