On Mon, 23 Aug 2010, Sarah Sharp wrote: > I heard that Windows developers have encountered USB devices that don't > remember their "brains" (configuration/alt settings) across a system > suspend or hibernate. Do we have any such work-arounds in Linux? What > happens if a device thinks it's using alt setting 0, and the USB core > thinks alt setting 1 is used after a resume? If the host controller or device needs to be reset during resume then we expect the device to lose its settings, and the device is told to get to its previous config and altsetting values. This happens in usb_reset_and_verify_device. BTW, we generally do have to reset everything following hibernation -- the assumption is that everything got wiped out when the boot kernel was loaded. However if the power session was not disrupted during the system sleep then we expect the device to maintain its old settings unless the USB_QUIRK_RESET_RESUME flag is set, as Oliver pointed out. If a device thinks its using a different altsetting from what the system thinks, it probably won't work. 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
