[PATCH v2 2/3] Documentation: tracing: Add PCI controller event documentation

[Shawn Lin]

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 at 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
+* ``state`` - PCIe LTSSM state
+* ``rate`` - PCIe bus speed
+
+**Example Usage**:
+
+    # Enable the tracepoint
+    echo 1 > /sys/kernel/debug/tracing/events/pci/pcie_ltssm_state_transition/enable
+
+    # Monitor events (the following output is generated when a device is linking)
+    cat /sys/kernel/debug/tracing/trace_pipe
+       kworker/0:0-9       [000] .....     5.600221: pcie_ltssm_state_transition: dev: a40000000.pcie state: RCVRY_EQ2 rate: 8.0 GT/s
-- 
2.7.4