On Mon, 17 Dec 2001, Vojtech Pavlik wrote: > > Well, as explained in the other posting, suspend/resume is pretty much > > different from unplug/replug because a suspended device is still drawing > > some power from the suspended USB. This way even a buspowered device can > > keep its state and the host can be sure, it's still the same device which > > he will resume later on. > > How? The host will not be notified when the device is unplugged and > replugged while suspended.
The HC has to monitor the USB state anyway - at least if it supports remote wakeup. A device which signals remote wakeup executes exactly a simulated disconnect/reconnect cycle on the USB which triggers the host to resume, if enabled. If the host is unable to monitor the bus state (I don't know whether this applies to _any_ HC D* state), you are right, it can't tell. But in this case the HC is required to signal a connect when resuming operation anyway - it's all in chapter 9 of the USB specs. > > For unplug/replug OTOH I agree it's a good idea to have the device keep > > its state as much as it makes sense - but the host _must not_ make any > > assumption here because the replugged device might just be a different one > > or might have been plugged to a different host meanwhile. > > The host should pass all the relevant information to an userspace agent, > which can then decide (even can let the user decide if really needed) > whether it is the same device and should be used as such or not. Do you really believe in average users' ability to decide whether a device which was connected to a different box meanwhile is still the "same" device? > You usually will want a replacement device just work without having to > restart all the programs using it. So you wan't the application which has open files on a usb-disk to continue writing to these files if there is a replacement device there after suspend/resume (with unplug/replug)? I doubt that's what you wanted to say? IMHO the HC+HCD can tell whether this can be treated as a resume or not. If not, the application shall be forced to close all open files... Martin _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
