Is there any recommendation about what to do when a driver is probed for a suspended device? Probably most drivers don't bother to check the device state; if they encounter errors because the device doesn't respond the way they expect, the probe will simply fail. (The USB subsystem, for example, doesn't take this into account.) One possible answer is that this should be handled at the bus level -- the bus subsystem could be responsible for setting a device to full power before probing, or it could rely on individual device drivers doing whatever they need. It would be nicer if a common solution could be found that would work uniformly for all devices and buses. (As part of such a solution, buses could have a standard policy that devices with no driver should be left in a low-power state.) A related problem is faced by USB drivers in a boot kernel. The current design relies on USB devices maintaining their state across a suspend/resume, even suspend to disk. This makes things difficult when resuming from disk; the boot kernel has to realize that it shouldn't disturb the state of any USB devices. At the moment this isn't handled very well. For instance, it would be largely a matter of luck if you could do STD with the image stored in a swap partition on a USB storage device. In fact, maybe it's a mistake to expect USB devices to maintain their state across STD. After all, devices on the motherboard aren't expected to; it's generally accepted that drivers will restore whatever state is necessary as part of their resume procedure. Why shouldn't USB devices behave the same way? Alan Stern
