[PATCH v10 3/3] Documentation: tracing: Add documentation about PCI tracepoints

Shuai Xue
2025-09-20T06:01:32Z

The PCI tracing system provides tracepoints to monitor critical hardware
events that can impact system performance and reliability. Add
documentation about it.

Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
---
Documentation/trace/events-pci.rst | 74 ++++++++++++++++++++++++++++++
1 file changed, 74 insertions(+)
create mode 100644 Documentation/trace/events-pci.rst

diff --git a/Documentation/trace/events-pci.rst b/Documentation/trace/events-pci.rst
new file mode 100644
index 000000000000..500b27713224
--- /dev/null
+++ b/Documentation/trace/events-pci.rst
@@ -0,0 +1,74 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========================
+Subsystem Trace Points: PCI
+===========================
+
+Overview
+========
+The PCI tracing system provides tracepoints to monitor critical hardware events
+that can impact system performance and reliability. These events normally show
+up here:
+
+ /sys/kernel/tracing/events/pci
+
+Cf. include/trace/events/pci.h for the events definitions.
+
+Available Tracepoints
+=====================
+
+pci_hp_event
+------------
+
+Monitors PCI hotplug events including card insertion/removal and link
+state changes.
+::
+
+ pci_hp_event "%s slot:%s, event:%s\n"
+
+**Event Types**:
+
+* ``LINK_UP`` - PCIe link established
+* ``LINK_DOWN`` - PCIe link lost
+* ``CARD_PRESENT`` - Card detected in slot
+* ``CARD_NOT_PRESENT`` - Card removed from slot
+
+**Example Usage**:
+
+ # Enable the tracepoint
+ echo 1> /sys/kernel/debug/tracing/events/pci/pci_hp_event/enable
+
+ # Monitor events (the following output is generated when a device is hotplugged)
+ cat /sys/kernel/debug/tracing/trace_pipe
+ irq/51-pciehp-88 [001] ..... 1311.177459: pci_hp_event: 0000:00:02.0 slot:10, event:CARD_PRESENT
+
+ irq/51-pciehp-88 [001] ..... 1311.177566: pci_hp_event: 0000:00:02.0 slot:10, event:LINK_UP
+
+pcie_link_event
+---------------
+
+Monitors PCIe link speed changes and provides detailed link status information.
+::
+
+ pcie_link_event "%s type:%d, reason:%d, cur_bus_speed:%s, max_bus_speed:%s, width:%u, flit_mode:%u, status:%s\n"
+
+**Parameters**:
+
+* ``type`` - PCIe device type (4=Root Port, etc.)
+* ``reason`` - Reason for link change:
+
+ - ``0`` - Link retrain
+ - ``1`` - Bus enumeration
+ - ``2`` - Bandwidth controller enable
+ - ``3`` - Bandwidth controller IRQ
+ - ``4`` - Hotplug event
+
+
+**Example Usage**:
+
+ # Enable the tracepoint
+ echo1 > /sys/kernel/debug/tracing/events/pci/pcie_link_event/enable
+
+ # Monitor events (the following output is generated when a device is hotplugged)
+ cat /sys/kernel/debug/tracing/trace_pipe
+ irq/51-pciehp-88 [001] ..... 381.545386: pcie_link_event: 0000:00:02.0 type:4, reason:4, cur_bus_speed:2.5 GT/s PCIe, max_bus_speed:16.0 GT/s PCIe, width:1, flit_mode:0, status:DLLLA
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2.39.3