On Thu, 22 Jan 2026, Shawn Lin wrote:
> Some platforms may provide LTSSM trace functionality, recording historical
> LTSSM state transition information. This is very useful for debugging, such
> as when certain devices cannot be recognized or link broken during test.
> Implement the pci controller tracepoint for recording LTSSM and rate.
>
> Signed-off-by: Shawn Lin <[email protected]>
> ---
>
> Changes in v4:
> - use TRACE_EVENT_FN to notify when to start and stop the tracepoint,
> and export pci_ltssm_tp_enabled() for host drivers to use
>
> Changes in v3:
> - add TRACE_DEFINE_ENUM for all enums(Steven Rostedt)
>
> Changes in v2: None
>
> drivers/pci/trace.c | 20 ++++++++++++
> include/linux/pci.h | 4 +++
> include/trace/events/pci_controller.h | 57
> +++++++++++++++++++++++++++++++++++
> 3 files changed, 81 insertions(+)
> create mode 100644 include/trace/events/pci_controller.h
>
> diff --git a/drivers/pci/trace.c b/drivers/pci/trace.c
> index cf11abc..d351a51 100644
> --- a/drivers/pci/trace.c
> +++ b/drivers/pci/trace.c
> @@ -9,3 +9,23 @@
>
> #define CREATE_TRACE_POINTS
> #include <trace/events/pci.h>
> +#include <trace/events/pci_controller.h>
> +
> +static atomic_t pcie_ltssm_tp_enabled = ATOMIC_INIT(0);
> +
> +bool pci_ltssm_tp_enabled(void)
> +{
> + return atomic_read(&pcie_ltssm_tp_enabled) > 0;
> +}
> +EXPORT_SYMBOL(pci_ltssm_tp_enabled);
> +
> +int pci_ltssm_tp_reg(void)
> +{
> + atomic_inc(&pcie_ltssm_tp_enabled);
> + return 0;
> +}
> +
> +void pci_ltssm_tp_unreg(void)
> +{
> + atomic_dec(&pcie_ltssm_tp_enabled);
> +}
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index e7cb527..ac25a3e 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2770,6 +2770,10 @@ static inline struct eeh_dev
> *pci_dev_to_eeh_dev(struct pci_dev *pdev)
> }
> #endif
>
> +#ifdef CONFIG_TRACING
> +bool pci_ltssm_tp_enabled(void);
> +#endif
> +
> void pci_add_dma_alias(struct pci_dev *dev, u8 devfn_from, unsigned
> nr_devfns);
> bool pci_devs_are_dma_aliases(struct pci_dev *dev1, struct pci_dev *dev2);
> int pci_for_each_dma_alias(struct pci_dev *pdev,
> diff --git a/include/trace/events/pci_controller.h
> b/include/trace/events/pci_controller.h
> new file mode 100644
> index 0000000..db4a960
> --- /dev/null
> +++ b/include/trace/events/pci_controller.h
> @@ -0,0 +1,57 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM pci_controller
I find putting this into "pci_controller" little odd as LTSSM is related
to PCIe links/ports. To me looks something that belongs to the existing
include/trace/events/pci.h.
> +#if !defined(_TRACE_HW_EVENT_PCI_CONTROLLER_H) ||
> defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_HW_EVENT_PCI_CONTROLLER_H
> +
> +#include <uapi/linux/pci_regs.h>
> +#include <linux/tracepoint.h>
> +
> +TRACE_DEFINE_ENUM(PCIE_SPEED_2_5GT);
> +TRACE_DEFINE_ENUM(PCIE_SPEED_5_0GT);
> +TRACE_DEFINE_ENUM(PCIE_SPEED_8_0GT);
> +TRACE_DEFINE_ENUM(PCIE_SPEED_16_0GT);
> +TRACE_DEFINE_ENUM(PCIE_SPEED_32_0GT);
> +TRACE_DEFINE_ENUM(PCIE_SPEED_64_0GT);
> +TRACE_DEFINE_ENUM(PCI_SPEED_UNKNOWN);
> +
> +extern int pci_ltssm_tp_reg(void);
> +extern void pci_ltssm_tp_unreg(void);
> +
> +TRACE_EVENT_FN(pcie_ltssm_state_transition,
> + TP_PROTO(const char *dev_name, const char *state, u32 rate),
> + TP_ARGS(dev_name, state, rate),
> +
> + TP_STRUCT__entry(
> + __string(dev_name, dev_name)
> + __string(state, state)
> + __field(u32, rate)
> + ),
> +
> + TP_fast_assign(
> + __assign_str(dev_name);
> + __assign_str(state);
> + __entry->rate = rate;
> + ),
> +
> + TP_printk("dev: %s state: %s rate: %s",
> + __get_str(dev_name), __get_str(state),
> + __print_symbolic(__entry->rate,
> + { PCIE_SPEED_2_5GT, "2.5 GT/s" },
> + { PCIE_SPEED_5_0GT, "5.0 GT/s" },
> + { PCIE_SPEED_8_0GT, "8.0 GT/s" },
> + { PCIE_SPEED_16_0GT, "16.0 GT/s" },
> + { PCIE_SPEED_32_0GT, "32.0 GT/s" },
> + { PCIE_SPEED_64_0GT, "64.0 GT/s" },
> + { PCI_SPEED_UNKNOWN, "Unknown" }
Why are these done inline instead of using EM/EMe()? Or simply with
pci_speed_string()?
Unrelated to this, sadly I failed to notice Shuai's version of
pcie_link_event() did not translate link speeds (my own version used
pci_speed_string()).
> + )
> + ),
> +
> + pci_ltssm_tp_reg, pci_ltssm_tp_unreg
> +);
> +
> +#endif /* _TRACE_HW_EVENT_PCI_CONTROLLER_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
>
--
i.
