[PATCH v12 2/3] PCI: trace: Add a RAS tracepoint to monitor link speed changes

Shuai Xue
2025-10-14T12:32:14Z

PCIe link speed degradation directly impacts system performance and
often indicates hardware issues such as faulty devices, physical layer
problems, or configuration errors.

To this end, add a RAS tracepoint to monitor link speed changes,
enabling proactive health checks and diagnostic analysis.

The following output is generated when a device is hotplugged:

$ echo 1 > /sys/kernel/debug/tracing/events/pci/pcie_link_event/enable
$ 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

Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Suggested-by: Matthew W Carlis <mattc@purestorage.com>
Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
---
drivers/pci/hotplug/pciehp_hpc.c | 3 +-
drivers/pci/pci.c | 2 +-
drivers/pci/pci.h | 22 ++++++++++--
drivers/pci/pcie/bwctrl.c | 4 +--
drivers/pci/probe.c | 9 +++--
include/linux/pci.h | 1 +
include/trace/events/pci.h | 57 ++++++++++++++++++++++++++++++++
7 files changed, 88 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index bcc51b26d03d..ad5f28f6a8b1 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -320,7 +320,8 @@ int pciehp_check_link_status(struct controller *ctrl)
}

pcie_capability_read_word(pdev, PCI_EXP_LNKSTA2, &linksta2);
- __pcie_update_link_speed(ctrl->pcie->port->subordinate, lnk_status, linksta2);
+ __pcie_update_link_speed(ctrl->pcie->port->subordinate, PCIE_HOTPLUG,
+ lnk_status, linksta2);

if (!found) {
ctrl_info(ctrl, "Slot(%s): No device found\n",
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b14dd064006c..6a979a234fe6 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4698,7 +4698,7 @@ int pcie_retrain_link(struct pci_dev *pdev, bool use_lt)
* Link Speed.
*/
if (pdev->subordinate)
- pcie_update_link_speed(pdev->subordinate);
+ pcie_update_link_speed(pdev->subordinate, PCIE_LINK_RETRAIN);

return rc;
}
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 4492b809094b..fff30521ed83 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -5,6 +5,7 @@
#include <linux/align.h>
#include <linux/bitfield.h>
#include <linux/pci.h>
+#include <trace/events/pci.h>

struct pcie_tlp_log;

@@ -549,16 +550,31 @@ static inline int pcie_dev_speed_mbps(enum pci_bus_speed speed)
}

u8 pcie_get_supported_speeds(struct pci_dev *dev);
-const char *pci_speed_string(enum pci_bus_speed speed);
void __pcie_print_link_status(struct pci_dev *dev, bool verbose);
void pcie_report_downtraining(struct pci_dev *dev);

-static inline void __pcie_update_link_speed(struct pci_bus *bus, u16 linksta, u16 linksta2)
+enum pcie_link_change_reason {
+ PCIE_LINK_RETRAIN,
+ PCIE_ADD_BUS,
+ PCIE_BWCTRL_ENABLE,
+ PCIE_BWCTRL_IRQ,
+ PCIE_HOTPLUG,
+};
+
+static inline void __pcie_update_link_speed(struct pci_bus *bus,
+ enum pcie_link_change_reason reason,
+ u16 linksta, u16 linksta2)
{
bus->cur_bus_speed = pcie_link_speed[linksta & PCI_EXP_LNKSTA_CLS];
bus->flit_mode = (linksta2 & PCI_EXP_LNKSTA2_FLIT) ? 1 : 0;
+
+ trace_pcie_link_event(bus,
+ reason,
+ FIELD_GET(PCI_EXP_LNKSTA_NLW, linksta),
+ linksta & PCI_EXP_LNKSTA_LINK_STATUS_MASK);
}
-void pcie_update_link_speed(struct pci_bus *bus);
+
+void pcie_update_link_speed(struct pci_bus *bus, enum pcie_link_change_reason reason);

/* Single Root I/O Virtualization */
struct pci_sriov {
diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
index 36f939f23d34..32f1b30ecb84 100644
--- a/drivers/pci/pcie/bwctrl.c
+++ b/drivers/pci/pcie/bwctrl.c
@@ -199,7 +199,7 @@ static void pcie_bwnotif_enable(struct pcie_device *srv)
* Update after enabling notifications & clearing status bits ensures
* link speed is up to date.
*/
- pcie_update_link_speed(port->subordinate);
+ pcie_update_link_speed(port->subordinate, PCIE_BWCTRL_ENABLE);
}

static void pcie_bwnotif_disable(struct pci_dev *port)
@@ -234,7 +234,7 @@ static irqreturn_t pcie_bwnotif_irq(int irq, void *context)
* speed (inside pcie_update_link_speed()) after LBMS has been
* cleared to avoid missing link speed changes.
*/
- pcie_update_link_speed(port->subordinate);
+ pcie_update_link_speed(port->subordinate, PCIE_BWCTRL_IRQ);

return IRQ_HANDLED;
}
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index c83e75a0ec12..d52f997ea476 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -22,6 +22,7 @@
#include <linux/irqdomain.h>
#include <linux/pm_runtime.h>
#include <linux/bitfield.h>
+#include <trace/events/pci.h>
#include "pci.h"

#define CARDBUS_LATENCY_TIMER 176 /* secondary latency timer */
@@ -813,14 +814,16 @@ const char *pci_speed_string(enum pci_bus_speed speed)
}
EXPORT_SYMBOL_GPL(pci_speed_string);

-void pcie_update_link_speed(struct pci_bus *bus)
+void pcie_update_link_speed(struct pci_bus *bus,
+ enum pcie_link_change_reason reason)
{
struct pci_dev *bridge = bus->self;
u16 linksta, linksta2;

pcie_capability_read_word(bridge, PCI_EXP_LNKSTA, &linksta);
pcie_capability_read_word(bridge, PCI_EXP_LNKSTA2, &linksta2);
- __pcie_update_link_speed(bus, linksta, linksta2);
+
+ __pcie_update_link_speed(bus, reason, linksta, linksta2);
}
EXPORT_SYMBOL_GPL(pcie_update_link_speed);

@@ -907,7 +910,7 @@ static void pci_set_bus_speed(struct pci_bus *bus)
pcie_capability_read_dword(bridge, PCI_EXP_LNKCAP, &linkcap);
bus->max_bus_speed = pcie_link_speed[linkcap & PCI_EXP_LNKCAP_SLS];

- pcie_update_link_speed(bus);
+ pcie_update_link_speed(bus, PCIE_ADD_BUS);
}
}

diff --git a/include/linux/pci.h b/include/linux/pci.h
index d1fdf81fbe1e..f35a5b8522af 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -306,6 +306,7 @@ enum pci_bus_speed {
PCI_SPEED_UNKNOWN = 0xff,
};

+const char *pci_speed_string(enum pci_bus_speed speed);
enum pci_bus_speed pcie_get_speed_cap(struct pci_dev *dev);
enum pcie_link_width pcie_get_width_cap(struct pci_dev *dev);

diff --git a/include/trace/events/pci.h b/include/trace/events/pci.h
index 208609492c06..4df4daaa2d27 100644
--- a/include/trace/events/pci.h
+++ b/include/trace/events/pci.h
@@ -5,6 +5,7 @@
#if !defined(_TRACE_HW_EVENT_PCI_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_HW_EVENT_PCI_H

+#include <uapi/linux/pci_regs.h>
#include <linux/tracepoint.h>

#define PCI_HOTPLUG_EVENT \
@@ -57,6 +58,62 @@ TRACE_EVENT(pci_hp_event,
)
);

+#define PCI_EXP_LNKSTA_LINK_STATUS_MASK (PCI_EXP_LNKSTA_LBMS | \
+ PCI_EXP_LNKSTA_LABS | \
+ PCI_EXP_LNKSTA_LT | \
+ PCI_EXP_LNKSTA_DLLLA)
+
+#define LNKSTA_FLAGS \
+ { PCI_EXP_LNKSTA_LT, "LT"}, \
+ { PCI_EXP_LNKSTA_DLLLA, "DLLLA"}, \
+ { PCI_EXP_LNKSTA_LBMS, "LBMS"}, \
+ { PCI_EXP_LNKSTA_LABS, "LABS"}
+
+TRACE_EVENT(pcie_link_event,
+
+ TP_PROTO(struct pci_bus *bus,
+ unsigned int reason,
+ unsigned int width,
+ unsigned int status
+ ),
+
+ TP_ARGS(bus, reason, width, status),
+
+ TP_STRUCT__entry(
+ __string( port_name, pci_name(bus->self))
+ __field( unsigned int, type )
+ __field( unsigned int, reason )
+ __field( unsigned int, cur_bus_speed )
+ __field( unsigned int, max_bus_speed )
+ __field( unsigned int, width )
+ __field( unsigned int, flit_mode )
+ __field( unsigned int, link_status )
+ ),
+
+ TP_fast_assign(
+ __assign_str(port_name);
+ __entry->type = pci_pcie_type(bus->self);
+ __entry->reason = reason;
+ __entry->cur_bus_speed = bus->cur_bus_speed;
+ __entry->max_bus_speed = bus->max_bus_speed;
+ __entry->width = width;
+ __entry->flit_mode = bus->flit_mode;
+ __entry->link_status = status;
+ ),
+
+ TP_printk("%s type:%d, reason:%d, cur_bus_speed:%s, max_bus_speed:%s, width:%u, flit_mode:%u, status:%s\n",
+ __get_str(port_name),
+ __entry->type,
+ __entry->reason,
+ pci_speed_string(__entry->cur_bus_speed),
+ pci_speed_string(__entry->max_bus_speed),
+ __entry->width,
+ __entry->flit_mode,
+ __print_flags((unsigned long)__entry->link_status, "|",
+ LNKSTA_FLAGS)
+ )
+);
+
#endif /* _TRACE_HW_EVENT_PCI_H */

/* This part must be outside protection */
--
2.39.3