Some PCI controllers may provide debug functionalities to track PCI bus
activities like LTSSM state transitions and data rate changes. These will
be very useful for debugging PCI link specific issues such as endpoint not
getting detected or performance issues.

Hence, implement the PCI controller tracepoint feature for recording LTSSM
state transitions and data rate changes.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
[mani: commit log and maintainers entry]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Tested-by: Anand Moon <linux.amoon@gmail.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://patch.msgid.link/1774403912-210670-2-git-send-email-shawn.lin@rock-chips.com

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>
Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> # for trace event
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://patch.msgid.link/20251210132907.58799-2-xueshuai@linux.alibaba.com