On Wed, 2013-08-14 at 14:46 +0530, Vivek Gautam wrote: Hi, > >> devices and root-hubs across suspend/resume. Are the device contexts > >> saved somewhere and then restored back on resume ? > > > > Usually not. The state of interfaces are the responsibility of interface > > drivers (colloquially called device drivers). Most devices just don't > > offer an API for saving state. The drivers recreate as opposed to > > restore the state. > > How does then PERSIST_ENABLED option work then ? With this option enabled, > on a system resume, the USB device attached to the root-hub are not > re-enumerated, right ? Exactly that way. You recreate the state of the device. > Possibly i am getting confused here. Well. There are two ways to make a device go to the same state a) you have primitives to save and restore that state b) you recognize that the state is the result of a sequence of operations. You repeat that sequence. That is the basic idea from a high level of abstraction. > How would a usb_suspend_interface() and usb_suspend_device() differ. Have a look at drivers/usb/core/generic.c > Is it that, from the interface only the device information is extracted ? > Can't we catch hold of usb_device pointers of hub and child devices ? We can. And that is how persist works. But it may fail. Possibly I am misunderstanding you. Regards Oliver -- 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
