Re: [PATCH v10 1/3] PCI: trace: Add a generic RAS tracepoint for hotplug event

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Sat, 20 Sep 2025, Shuai Xue wrote:

> Hotplug events are critical indicators for analyzing hardware health,
> and surprise link downs can significantly impact system performance and
> reliability.
> 
> Define a new TRACING_SYSTEM named "pci", add a generic RAS tracepoint
> for hotplug event to help health checks. Add enum pci_hotplug_event in
> include/uapi/linux/pci.h so applications like rasdaemon can register
> tracepoint event handlers for it.
> 
> The following output is generated when a device is hotplugged:
> 
> $ echo 1 > /sys/kernel/debug/tracing/events/pci/pci_hp_event/enable
> $ 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
> 
> 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>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
>  drivers/pci/Makefile              |  2 +
>  drivers/pci/hotplug/Makefile      |  3 +-
>  drivers/pci/hotplug/pciehp_ctrl.c | 31 ++++++++++++---
>  drivers/pci/trace.c               | 11 ++++++
>  include/trace/events/pci.h        | 63 +++++++++++++++++++++++++++++++
>  include/uapi/linux/pci.h          |  7 ++++
>  6 files changed, 110 insertions(+), 7 deletions(-)
>  create mode 100644 drivers/pci/trace.c
>  create mode 100644 include/trace/events/pci.h
> 
> diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
> index 67647f1880fb..bf389bc4dd3c 100644
> --- a/drivers/pci/Makefile
> +++ b/drivers/pci/Makefile
> @@ -45,3 +45,5 @@ obj-y				+= controller/
>  obj-y				+= switch/
>  
>  subdir-ccflags-$(CONFIG_PCI_DEBUG) := -DDEBUG
> +
> +CFLAGS_trace.o := -I$(src)
> diff --git a/drivers/pci/hotplug/Makefile b/drivers/pci/hotplug/Makefile
> index 40aaf31fe338..d41f7050b072 100644
> --- a/drivers/pci/hotplug/Makefile
> +++ b/drivers/pci/hotplug/Makefile
> @@ -65,7 +65,8 @@ rpadlpar_io-objs	:=	rpadlpar_core.o \
>  pciehp-objs		:=	pciehp_core.o	\
>  				pciehp_ctrl.o	\
>  				pciehp_pci.o	\
> -				pciehp_hpc.o
> +				pciehp_hpc.o	\
> +				../trace.o

To make it useful for any PCI tracing, not juse hotplug, this object file 
should be added in drivers/pci/Makefile, not here.

>  shpchp-objs		:=	shpchp_core.o	\
>  				shpchp_ctrl.o	\
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index bcc938d4420f..7805f697a02c 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -19,6 +19,7 @@
>  #include <linux/types.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/pci.h>
> +#include <trace/events/pci.h>
>  
>  #include "../pci.h"
>  #include "pciehp.h"
> @@ -244,12 +245,20 @@ 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 +278,9 @@ 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 +293,19 @@ 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/trace.c b/drivers/pci/trace.c
> new file mode 100644
> index 000000000000..cf11abca8602
> --- /dev/null
> +++ b/drivers/pci/trace.c
> @@ -0,0 +1,11 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Tracepoints for PCI system
> + *
> + * Copyright (C) 2025 Alibaba Corporation
> + */
> +
> +#include <linux/pci.h>
> +
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/pci.h>
> diff --git a/include/trace/events/pci.h b/include/trace/events/pci.h
> new file mode 100644
> index 000000000000..208609492c06
> --- /dev/null
> +++ b/include/trace/events/pci.h
> @@ -0,0 +1,63 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM pci
> +
> +#if !defined(_TRACE_HW_EVENT_PCI_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_HW_EVENT_PCI_H
> +
> +#include <linux/tracepoint.h>
> +
> +#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_H */
> +
> +/* 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 */
> 

-- 
 i.