On Thu, 2012-05-10 at 11:54 -0400, Alan Stern wrote: > On Thu, 10 May 2012, Lan Tianyu wrote: > > > hi all: > > Currently, we are working on usb port power off mechanism. Our developing > > machine provides usb port power control (a vbus switch)via ACPI power resource. > > When the power resource turns off, usb port powers off and usb device loses > > power. From usb hub side, just like the device being unplugged. > > > > Since usb port power off will affect hot-plug and devices remote wakeup > > function, it should be careful to do that. > > We conclude three different situations for power off mechanism. > > (1) hard-wired port with device > > (2) hot-pluggable port without device > > (3) hot-pluggable port with device > > > > For hard-wired port, the device will not be removed physically. So we can > > power off it when device is suspended and remote wakeup is disabled without > > concerning with hot-plug. This patch is dedicated to this siutation. > > > > This patch is to provide usb acpi power control method and call them in the > > usb_port_suspend() and usb_port_resume() when port can be power off. When the > > usb port is in the power off state, usb core doesn't remove device which is > > attached to the port. The device is still on the system and user can access > > the device. > > Can you provide any examples where this would be useful? It won't end > up saving very much power (although on a laptop even a little bit might > help). I'd love to do this with ModemManager to shoot a modem in the head if it's crashed. Right now there's simply no way to reset a device that's misbehaving or crashed. Powering off the port would be a last resort, but not all devices actually disconnect from the bus when they crash and reconnect after the firmware reboots. Dan > > introduce three port's states. > > > > USB_PORT_POWER_STATE_ON > > USB_PORT_WAITING_FOR_CONNECTION > > USB_PORT_POWER_STATE_OFF > > > > "on" > > port power on > > > > "waiting for connection" > > port power on but hub port has not detected the device or detect event has > > not been processed. > > This state is not needed. > > > "off" > > port power off > > > > At first, port's state is "on". When the device is suspended, power off the port and > > set port's state to "off". After the port powering off, the usb hub will detect a > > connection change event. Normally, the device will be removed with regarding as being > > unplugged. But in the power off mechanism, the device is still on the port and user > > can still access the device. So ignore the event. > > > > When the device is resumed, turn on the power resource and set port's state to > > "waiting for connection". After the port powering on, the usb hub will detect a > > connection change event which originally means a device plugged in and previous > > device will be removed. But in the power offmechanism, the device is not changed > > and so ignore the event. When port's state is "waiting for connection", receive > > an event "connection" and the port's connection state is on. This means the usb > > the device is detected by usb hub again after powering on port. Set port's state > > to "on". > > > > "on" > > | > > "off" > > | > > "waiting for connection" > > | > > "on" > > > > "waiting for connection" state is to avoid device to being removed. > > Why would the device be removed? > > > If set to "on" after powering on, the connection event may not be processed at that > > time. When it is processed, the port's state has been "on" and the device will be > > removed. So introduce "waiting for connection" state. > > Instead you should simply delay setting the state back to "on" until > the device has connected. > > > We also have a proposal to add sys file for each port to control port power off > > under usb hub sys directory. If the port's power off is supported by platform, > > create a sys file e.g "port1_power" for port one. Echo "on" to "port1_power" is > > to not allow port to be power off. Echo "auto" to "port1_power" is to power off > > port if possible. > > > > Different type ports have different default values. > > (1) hard-wired port with device "auto" > > (2) hot-pluggable port without device "on" > > (3) hot-pluggable port with device "on" > > > > Add member port_power_control, can_power_off to struct usb_hub_port. port_power_control > > records user choice. Can_power_off means the platform and device support to power off. > > When a device is attached, check whether port can be power off if yes set can_power_off > > to true. When device driver is load, the driver also can set value to can_power_off. When > > That's no good. What happens if the driver sets the value to false and > then the driver is unloaded? > > > try to power off port, can_power_off and port_power_control should be taken into account. > > Only when these two members are set to true, the port could be power off. > > > > sys file operation > > port with device > > port1_power "auto" => "on" or "on" => "auto" implement > > pm_runtime_get_syn(udev) > > port_power_control = "auto" or "on" > > pm_runtime_put_syn(udev) > > > > port without device > > port can power on or power power off directly. > > We have no code for powering off ports that don't have a device. If > you did power off such a port, it would not be able to detect when a > device was plugged in. > > > Suggestion and comments more welcome. > > Your code style for continuation lines is wrong. Continuation lines > should be indented more than one tab stop -- otherwise they look like > regular lines in an inner block. > > 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 -- 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
