The available tracepoint, pcie_ltssm_state_transition, monitors the LTSSM state
transistion for debugging purpose. Add description about it.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
---

Changes in v2: None

 Documentation/trace/events-pci-conotroller.rst | 41 ++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 Documentation/trace/events-pci-conotroller.rst

diff --git a/Documentation/trace/events-pci-conotroller.rst b/Documentation/trace/events-pci-conotroller.rst
new file mode 100644
index 0000000..8253d00
--- /dev/null
+++ b/Documentation/trace/events-pci-conotroller.rst

@@ -0,0 +1,41 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======================================
+Subsystem Trace Points: PCI Controller
+======================================
+
+Overview
+========
+The PCI controller tracing system provides tracepoints to monitor controller level
+information for debugging purpose. The events normally show up here:
+up here:
+
+	/sys/kernel/tracing/events/pci_controller
+
+Cf. include/trace/events/pci_controller.h for the events definitions.
+
+Available Tracepoints
+=====================
+
+pcie_ltssm_state_transition
+-----------------------
+
+Monitors PCIe LTSSM state transition including state and rate information
+::
+
+    pcie_ltssm_state_transition  "dev: %s state: %s rate: %s\n"
+
+**Parameters**:
+
+* ``dev`` - PCIe root port name