[PATCH v5] PCI: hotplug: Add a generic RAS tracepoint for hotplug event

[Shuai Xue <xueshuai@linux.alibaba.com>]

Hotplug events are critical indicators for analyzing hardware health,
particularly in AI supercomputers where surprise link downs can
significantly impact system performance and reliability.

To this end, define a new TRACING_SYSTEM named pci, add a generic RAS
tracepoint for hotplug event to help healthy check, and generate
tracepoints for pcie hotplug event. Add enum pci_hotplug_event in
include/uapi/linux/pci.h so applications like rasdaemon can register
tracepoint event handlers for it.

The output like below:

$ echo 1 > /sys/kernel/debug/tracing/events/pci/pci_hp_event/enable
$ cat /sys/kernel/debug/tracing/trace_pipe
    <...>-206     [001] .....    40.373870: pci_hp_event: 0000:00:02.0 slot:10, event:Link Down

    <...>-206     [001] .....    40.374871: pci_hp_event: 0000:00:02.0 slot:10, event:Card not present

Suggested-by: Lukas Wunner <lukas@wunner.de>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
---
change log since v4:
- rebase to pci/main (v6.13-rc1) (per Bjorn)
- rewrite commit log with generic motivation (per Bjorn)
---
 drivers/pci/hotplug/pciehp_ctrl.c | 33 ++++++++++++---
 drivers/pci/hotplug/trace.h       | 68 +++++++++++++++++++++++++++++++
 include/uapi/linux/pci.h          |  7 ++++
 3 files changed, 102 insertions(+), 6 deletions(-)
 create mode 100644 drivers/pci/hotplug/trace.h

diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
index d603a7aa7483..f9beb4d3a9b8 100644
--- a/drivers/pci/hotplug/pciehp_ctrl.c
+++ b/drivers/pci/hotplug/pciehp_ctrl.c
@@ -23,6 +23,9 @@
 #include "../pci.h"
 #include "pciehp.h"
 
+#define CREATE_TRACE_POINTS
+#include "trace.h"
+
 /* The following routines constitute the bulk of the
    hotplug controller logic
  */
@@ -244,12 +247,20 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
 	case ON_STATE:
 		ctrl->state = POWEROFF_STATE;
 		mutex_unlock(&ctrl->state_lock);
-		if (events & PCI_EXP_SLTSTA_DLLSC)
+		if (events & PCI_EXP_SLTSTA_DLLSC) {
 			ctrl_info(ctrl, "Slot(%s): Link Down\n",
 				  slot_name(ctrl));
-		if (events & PCI_EXP_SLTSTA_PDC)
+			trace_pci_hp_event(pci_name(ctrl->pcie->port),
+					   slot_name(ctrl),
+					   PCI_HOTPLUG_LINK_DOWN);
+		}
+		if (events & PCI_EXP_SLTSTA_PDC) {
 			ctrl_info(ctrl, "Slot(%s): Card not present\n",
 				  slot_name(ctrl));
+			trace_pci_hp_event(pci_name(ctrl->pcie->port),
+					   slot_name(ctrl),
+					   PCI_HOTPLUG_CARD_NOT_PRESENT);
+		}
 		pciehp_disable_slot(ctrl, SURPRISE_REMOVAL);
 		break;
 	default:
@@ -269,6 +280,9 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
 					      INDICATOR_NOOP);
 			ctrl_info(ctrl, "Slot(%s): Card not present\n",
 				  slot_name(ctrl));
+			trace_pci_hp_event(pci_name(ctrl->pcie->port),
+					   slot_name(ctrl),
+					   PCI_HOTPLUG_CARD_NOT_PRESENT);
 		}
 		mutex_unlock(&ctrl->state_lock);
 		return;
@@ -281,12 +295,19 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
 	case OFF_STATE:
 		ctrl->state = POWERON_STATE;
 		mutex_unlock(&ctrl->state_lock);
-		if (present)
+		if (present) {
 			ctrl_info(ctrl, "Slot(%s): Card present\n",
 				  slot_name(ctrl));
-		if (link_active)
-			ctrl_info(ctrl, "Slot(%s): Link Up\n",
-				  slot_name(ctrl));
+			trace_pci_hp_event(pci_name(ctrl->pcie->port),
+					   slot_name(ctrl),
+					   PCI_HOTPLUG_CARD_PRESENT);
+		}
+		if (link_active) {
+			ctrl_info(ctrl, "Slot(%s): Link Up\n", slot_name(ctrl));
+			trace_pci_hp_event(pci_name(ctrl->pcie->port),
+					   slot_name(ctrl),
+					   PCI_HOTPLUG_LINK_UP);
+		}
 		ctrl->request_result = pciehp_enable_slot(ctrl);
 		break;
 	default:
diff --git a/drivers/pci/hotplug/trace.h b/drivers/pci/hotplug/trace.h
new file mode 100644
index 000000000000..5b60cd7bcffb
--- /dev/null
+++ b/drivers/pci/hotplug/trace.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#if !defined(_TRACE_HW_EVENT_PCI_HP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_HW_EVENT_PCI_HP_H
+
+#include <linux/tracepoint.h>
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM pci
+
+#define PCI_HOTPLUG_EVENT					\
+	EM(PCI_HOTPLUG_LINK_UP,			"Link Up")	\
+	EM(PCI_HOTPLUG_LINK_DOWN,		"Link Down")	\
+	EM(PCI_HOTPLUG_CARD_PRESENT,		"Card present")	\
+	EMe(PCI_HOTPLUG_CARD_NOT_PRESENT,	"Card not present")
+
+/* Enums require being exported to userspace, for user tool parsing */
+#undef EM
+#undef EMe
+#define EM(a, b)	TRACE_DEFINE_ENUM(a);
+#define EMe(a, b)	TRACE_DEFINE_ENUM(a);
+
+PCI_HOTPLUG_EVENT
+
+/*
+ * Now redefine the EM() and EMe() macros to map the enums to the strings
+ * that will be printed in the output.
+ */
+#undef EM
+#undef EMe
+#define EM(a, b)	{a, b},
+#define EMe(a, b)	{a, b}
+
+TRACE_EVENT(pci_hp_event,
+
+	TP_PROTO(const char *port_name,
+		 const char *slot,
+		 const int event),
+
+	TP_ARGS(port_name, slot, event),
+
+	TP_STRUCT__entry(
+		__string(	port_name,	port_name	)
+		__string(	slot,		slot		)
+		__field(	int,		event	)
+	),
+
+	TP_fast_assign(
+		__assign_str(port_name);
+		__assign_str(slot);
+		__entry->event = event;
+	),
+
+	TP_printk("%s slot:%s, event:%s\n",
+		__get_str(port_name),
+		__get_str(slot),
+		__print_symbolic(__entry->event, PCI_HOTPLUG_EVENT)
+	)
+);
+
+#endif /* _TRACE_HW_EVENT_PCI_HP_H */
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH  ../../drivers/pci/hotplug
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_FILE trace
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/include/uapi/linux/pci.h b/include/uapi/linux/pci.h
index a769eefc5139..4f150028965d 100644
--- a/include/uapi/linux/pci.h
+++ b/include/uapi/linux/pci.h
@@ -39,4 +39,11 @@
 #define PCIIOC_MMAP_IS_MEM	(PCIIOC_BASE | 0x02)	/* Set mmap state to MEM space. */
 #define PCIIOC_WRITE_COMBINE	(PCIIOC_BASE | 0x03)	/* Enable/disable write-combining. */
 
+enum pci_hotplug_event {
+	PCI_HOTPLUG_LINK_UP,
+	PCI_HOTPLUG_LINK_DOWN,
+	PCI_HOTPLUG_CARD_PRESENT,
+	PCI_HOTPLUG_CARD_NOT_PRESENT,
+};
+
 #endif /* _UAPILINUX_PCI_H */
-- 
2.39.3