On 2013年03月30日 01:23, Alan Stern wrote: > On Fri, 29 Mar 2013, Sarah Sharp wrote: >> However, what happens if you echo 0 to pm_qos_no_power_off, the >> power/control is set to auto, and there's a suspended USB device >> attached to the port with remote wakeup enabled? Will the port be >> powered off? I don't think it will with the current patchset, but I >> will have to double check. > > It shouldn't be, because remote wakeup is enabled. But what about the > case where remote wakeup is disabled? Will writing a 0 to > pm_qos_no_power_off cause the power to be turned off? > > Or what about the case where there's no device attached to the port? I > guess both questions amount to the same thing: When the user writes to > a pm_qos_* file, does the code call pm_runtime_idle? > Usb port's initial usage count is 0. For port attached with usb port, when usb device is connected, the usb port's usage count is increased by one. During device's suspend, its usage count would be decreased to 0 and powered of only when remote wakeup disable, persist enable and PM Qos NO_POWER_OFF unsetting. During pm_qos_* file changing, pm_runtime_get_sync/put(port_dev) will be done in the dev_pm_qos_update_flags(). The port's usage count would be increased and decreased by 1. Whether the port's pm_runtime_idle would be called depends on port's usage count to be set to 0. If the usb port has already been powered off(port usage count is already set to 0), it would be powered on first and powered off depending the PM Qos NO_POWER_OFF flag value. If the usb port wasn't powered off, this mean the usb port didn't meet power off condition() and its usage count was still greater than 0 So during changing flag, only usage count was changed and no actual operation. For empty port, Only when PM Qos NO_POWER_OFF flag value is set to 0, the port will be power off. > > Alan Stern > -- Best regards Tianyu Lan -- 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
