** Changed in: linux (Ubuntu Bionic)
       Status: Triaged => In Progress

** Changed in: linux (Ubuntu Bionic)
     Assignee: Canonical Kernel Team (canonical-kernel-team) => Joseph 
Salisbury (jsalisbury)

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  [Feature] Add xHCI debug device support in the driver

Status in intel:
Status in linux package in Ubuntu:
  In Progress
Status in linux source package in Bionic:
  In Progress

Bug description:

  xHCI compatible USB host controllers(i.e. super-speed USB3 controllers)
  can be implemented with the Debug Capability(DbC). It presents a debug
  device which is fully compliant with the USB framework and provides the
  equivalent of a very high performance full-duplex serial link. The debug
  capability operation model and registers interface are defined in 7.6.8
  of the xHCI specification, revision 1.1.

  The DbC debug device shares a root port with the xHCI host. By default,
  the debug capability is disabled and the root port is assigned to xHCI.
  When the DbC is enabled, the root port will be assigned to the DbC debug
  device, and the xHCI sees nothing on this port. This implementation uses
  a sysfs node named <dbc> under the xHCI device to manage the enabling
  and disabling of the debug capability.

  When the debug capability is enabled, it will present a debug device
  through the debug port. This debug device is fully compliant with the
  USB3 framework, and it can be enumerated by a debug host on the other
  end of the USB link. As soon as the debug device is configured, a TTY
  serial device named /dev/ttyDBC0 will be created.

  One use of this link is running a login service on the debug target.
  Hence it can be remote accessed by a debug host. Another use case can
  probably be found in servers. It provides a peer-to-peer USB link
  between two host-only machines. This provides a reasonable out-of-band
  communication method between two servers.

  Target Kernel: 4.16
  Target Release: 18.04

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