On Mon, 12 Nov 2012, Lan Tianyu wrote: > >> I think port and device are bound. Power off port also means to power > >> off device. So prevent device from power off also means to prevent port > >> from power off. They just like a power domain. Because power is on the > >> port and so I thought we just needed to have pm qos flag on the port. > > > > Consider what happens when the device is unplugged. The restriction > > against powering off the device won't be needed any more, but the PM > > QOS flag will still be set for the port. > You are saying outside port. For outside port, currently our plan is to > set NO_POWER_OFF flag defaultly. So it doesn't matter after device > unplugged. What if the user changes the NO_POWER_OFF flag? It's only a default, so it can be changed. Once we have the PM QOS flag, do we need the NO_POWER_OFF flag any more? > Moreover, we can change the port's pm qos flag when device is > disconnected. But what if the user wants that port to remain powered on even after the device is disconnected? It seems to me the user might have good reasons to want to change the power-off behavior for a particular device, _or_ to change the power-off behavior for a particular port regardless of what device is plugged into 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
