USB: Enable Latency Tolerance Messaging (LTM):
USB 3.0 devices may optionally support a new feature called Latency Tolerance Messaging. If both the xHCI host controller and the device
support LTM, it should be turned on in order to give the system hardware a better clue about the latency tolerance values of its PCI devices.
Once a Set Feature request to enable LTM is received, the USB 3.0 device will begin to send LTM updates as its buffers fill or empty, and it can tolerate more or less latency.
The USB 3.0 spec says that LTM should be disabled just before the device is placed into suspend. Then the device will send an updated LTM notification.
So that the system doesn't think it should remain in an active state in order to satisfy the latency requirements of the suspended device.
The Set and Clear Feature LTM enable command can only be sent to a configured device. The device will respond with an error if that command is sent while it is in the Default or Addressed state.
Make sure to check the status of LTM. LTM should be enabled once a new configuration. If we end up sending duplicate Set Feature LTM Enable commands on a switch from one installed configuration to another
configuration, that should be harmless. Make sure that LTM is disabled before the device is unconfigured. If no drivers are bound to the device, it doesn't
make sense to allow the device to control the latency tolerance of the xHCI host controller.
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