On Wed, 21 Jul 2010, Sarah Sharp wrote: > > Okay, good. Could we put the link into a low-power state instead of > > disabling it? Ideally, a state from which it won't return to full > > power until there's a disconnect or a reset? > > Yes, I think we can. Link PM is designed to be handled by the devices > on the bus, not software, but there is commands to force devices into > lower power link states. SetPortFeature(PORT_LINK_STATE) = U1 or U2. > Figure 7-13 shows that if there's a device removal or a reset, then the > link state machine transitions back to Rx.Detect from any other state. > > However, the SetPortFeature(PORT_LINK_STATE) for U1 or U2 will fail if > the link isn't in U0 to start with. So we'd have to force the link into > U0 first, and then force it into U2. I think we would also have to > disable the U1 and U2 timers too, otherwise the device could transition > into U1 from U0 before we could force it into U2. > > This is starting to sound like something that should wait until link > power management is in place, though. It's not a big deal, so yes, it can wait. Actually I think we should put the device into suspend, if we can, instead of putting the link into U1 or U2. That would be pretty much equivalent to disabling the port anyway. 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
