Documentation: Add AMD Zen debugging document

Debugging issues on AMD hardware can be challenging for users without
proper documentation and tools.

Introduce a document that includes techniques for debugging s2idle
issues. It will be expanded for debugging other issues later.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Link: https://lore.kernel.org/20250422234830.2840784-2-superm1@kernel.org

Documentation/arch/x86/amd-debugging.rst

@@ -0,0 +1,320 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Debugging AMD Zen systems
++++++++++++++++++++++++++
+
+Introduction
+============
+
+This document describes techniques that are useful for debugging issues with
+AMD Zen systems.  It is intended for use by developers and technical users
+to help identify and resolve issues.
+
+S3 vs s2idle
+============
+
+On AMD systems, it's not possible to simultaneously support suspend-to-RAM (S3)
+and suspend-to-idle (s2idle).  To confirm which mode your system supports you
+can look at ``cat /sys/power/mem_sleep``.  If it shows ``s2idle [deep]`` then
+*S3* is supported.  If it shows ``[s2idle]`` then *s2idle* is
+supported.
+
+On systems that support *S3*, the firmware will be utilized to put all hardware into
+the appropriate low power state.
+
+On systems that support *s2idle*, the kernel will be responsible for transitioning devices
+into the appropriate low power state. When all devices are in the appropriate low
+power state, the hardware will transition into a hardware sleep state.
+
+After a suspend cycle you can tell how much time was spent in a hardware sleep
+state by looking at ``cat /sys/power/suspend_stats/last_hw_sleep``.
+
+This flowchart explains how the AMD s2idle suspend flow works.
+
+.. kernel-figure:: suspend.svg
+
+This flowchart explains how the amd s2idle resume flow works.
+
+.. kernel-figure:: resume.svg
+
+s2idle debugging tool
+=====================
+
+As there are a lot of places that problems can occur, a debugging tool has been
+created at
+`amd-debug-tools <https://git.kernel.org/pub/scm/linux/kernel/git/superm1/amd-debug-tools.git/about/>`_
+that can help test for common problems and offer suggestions.
+
+If you have an s2idle issue, it's best to start with this and follow instructions
+from its findings.  If you continue to have an issue, raise a bug with the
+report generated from this script to
+`drm/amd gitlab <https://gitlab.freedesktop.org/drm/amd/-/issues/new?issuable_template=s2idle_BUG_TEMPLATE>`_.
+
+Spurious s2idle wakeups from an IRQ
+===================================
+Spurious wakeups will generally have an IRQ set to ``/sys/power/pm_wakeup_irq``.
+This can be matched to ``/proc/interrupts`` to determine what device woke the system.
+
+If this isn't enough to debug the problem, then the following sysfs files
+can be set to add more verbosity to the wakeup process: ::
+
+  # echo 1 | sudo tee /sys/power/pm_debug_messages
+  # echo 1 | sudo tee /sys/power/pm_print_times
+
+After making those changes, the kernel will display messages that can
+be traced back to kernel s2idle loop code as well as display any active
+GPIO sources while waking up.
+
+If the wakeup is caused by the ACPI SCI, additional ACPI debugging may be
+needed.  These commands can enable additional trace data: ::
+
+  # echo enable | sudo tee /sys/module/acpi/parameters/trace_state
+  # echo 1 | sudo tee /sys/module/acpi/parameters/aml_debug_output
+  # echo 0x0800000f | sudo tee /sys/module/acpi/parameters/debug_level
+  # echo 0xffff0000 | sudo tee /sys/module/acpi/parameters/debug_layer
+
+Spurious s2idle wakeups from a GPIO
+===================================
+
+If a GPIO is active when waking up the system ideally you would look at the
+schematic to determine what device it is associated with. If the schematic
+is not available, another tactic is to look at the ACPI _EVT() entry
+to determine what device is notified when that GPIO is active.
+
+For a hypothetical example, say that GPIO 59 woke up the system.  You can
+look at the SSDT to determine what device is notified when GPIO 59 is active.
+
+First convert the GPIO number into hex. ::
+
+  $ python3 -c "print(hex(59))"
+  0x3b
+
+Next determine which ACPI table has the ``_EVT`` entry. For example: ::
+
+  $ sudo grep EVT /sys/firmware/acpi/tables/SSDT*
+  grep: /sys/firmware/acpi/tables/SSDT27: binary file matches
+
+Decode this table::
+
+  $ sudo cp /sys/firmware/acpi/tables/SSDT27 .
+  $ sudo iasl -d SSDT27
+
+Then look at the table and find the matching entry for GPIO 0x3b. ::
+
+  Case (0x3B)
+  {
+      M000 (0x393B)
+      M460 ("    Notify (\\_SB.PCI0.GP17.XHC1, 0x02)\n", Zero, Zero, Zero, Zero, Zero, Zero)
+      Notify (\_SB.PCI0.GP17.XHC1, 0x02) // Device Wake
+  }
+
+You can see in this case that the device ``\_SB.PCI0.GP17.XHC1`` is notified
+when GPIO 59 is active. It's obvious this is an XHCI controller, but to go a
+step further you can figure out which XHCI controller it is by matching it to
+ACPI.::
+
+  $ grep "PCI0.GP17.XHC1" /sys/bus/acpi/devices/*/path
+  /sys/bus/acpi/devices/device:2d/path:\_SB_.PCI0.GP17.XHC1
+  /sys/bus/acpi/devices/device:2e/path:\_SB_.PCI0.GP17.XHC1.RHUB
+  /sys/bus/acpi/devices/device:2f/path:\_SB_.PCI0.GP17.XHC1.RHUB.PRT1
+  /sys/bus/acpi/devices/device:30/path:\_SB_.PCI0.GP17.XHC1.RHUB.PRT1.CAM0
+  /sys/bus/acpi/devices/device:31/path:\_SB_.PCI0.GP17.XHC1.RHUB.PRT1.CAM1
+  /sys/bus/acpi/devices/device:32/path:\_SB_.PCI0.GP17.XHC1.RHUB.PRT2
+  /sys/bus/acpi/devices/LNXPOWER:0d/path:\_SB_.PCI0.GP17.XHC1.PWRS
+
+Here you can see it matches to ``device:2d``. Look at the ``physical_node``
+to determine what PCI device that actually is. ::
+
+  $ ls -l /sys/bus/acpi/devices/device:2d/physical_node
+  lrwxrwxrwx 1 root root 0 Feb 12 13:22 /sys/bus/acpi/devices/device:2d/physical_node -> ../../../../../pci0000:00/0000:00:08.1/0000:c2:00.4
+
+So there you have it: the PCI device associated with this GPIO wakeup was ``0000:c2:00.4``.
+
+The ``amd_s2idle.py`` script will capture most of these artifacts for you.
+
+s2idle PM debug messages
+========================
+During the s2idle flow on AMD systems, the ACPI LPS0 driver is responsible
+to check all uPEP constraints.  Failing uPEP constraints does not prevent
+s0i3 entry.  This means that if some constraints are not met, it is possible
+the kernel may attempt to enter s2idle even if there are some known issues.
+
+To activate PM debugging, either specify ``pm_debug_messagess`` kernel
+command-line option at boot or write to ``/sys/power/pm_debug_messages``.
+Unmet constraints will be displayed in the kernel log and can be
+viewed by logging tools that process kernel ring buffer like ``dmesg`` or
+``journalctl``."
+
+If the system freezes on entry/exit before these messages are flushed, a
+useful debugging tactic is to unbind the ``amd_pmc`` driver to prevent
+notification to the platform to start s0i3 entry.  This will stop the
+system from freezing on entry or exit and let you view all the failed
+constraints. ::
+
+  cd /sys/bus/platform/drivers/amd_pmc
+  ls | grep AMD | sudo tee unbind
+
+After doing this, run the suspend cycle and look specifically for errors around: ::
+
+  ACPI: LPI: Constraint not met; min power state:%s current power state:%s
+
+Historical examples of s2idle issues
+====================================
+To help understand the types of issues that can occur and how to debug them,
+here are some historical examples of s2idle issues that have been resolved.
+
+Core offlining
+--------------
+An end user had reported that taking a core offline would prevent the system
+from properly entering s0i3.  This was debugged using internal AMD tools
+to capture and display a stream of metrics from the hardware showing what changed
+when a core was offlined.  It was determined that the hardware didn't get
+notification the offline cores were in the deepest state, and so it prevented
+CPU from going into the deepest state. The issue was debugged to a missing
+command to put cores into C3 upon offline.
+
+`commit d6b88ce2eb9d2 ("ACPI: processor idle: Allow playing dead in C3 state") <https://git.kernel.org/torvalds/c/d6b88ce2eb9d2>`_
+
+Corruption after resume
+-----------------------
+A big problem that occurred with Rembrandt was that there was graphical
+corruption after resume.  This happened because of a misalignment of PSP
+and driver responsibility.  The PSP will save and restore DMCUB, but the
+driver assumed it needed to reset DMCUB on resume.
+This actually was a misalignment for earlier silicon as well, but was not
+observed.
+
+`commit 79d6b9351f086 ("drm/amd/display: Don't reinitialize DMCUB on s0ix resume") <https://git.kernel.org/torvalds/c/79d6b9351f086>`_
+
+Back to Back suspends fail
+--------------------------
+When using a wakeup source that triggers the IRQ to wakeup, a bug in the
+pinctrl-amd driver may capture the wrong state of the IRQ and prevent the
+system going back to sleep properly.
+
+`commit b8c824a869f22 ("pinctrl: amd: Don't save/restore interrupt status and wake status bits") <https://git.kernel.org/torvalds/c/b8c824a869f22>`_
+
+Spurious timer based wakeup after 5 minutes
+-------------------------------------------
+The HPET was being used to program the wakeup source for the system, however
+this was causing a spurious wakeup after 5 minutes.  The correct alarm to use
+was the ACPI alarm.
+
+`commit 3d762e21d5637 ("rtc: cmos: Use ACPI alarm for non-Intel x86 systems too") <https://git.kernel.org/torvalds/c/3d762e21d5637>`_
+
+Disk disappears after resume
+----------------------------
+After resuming from s2idle, the NVME disk would disappear.  This was due to the
+BIOS not specifying the _DSD StorageD3Enable property.  This caused the NVME
+driver not to put the disk into the expected state at suspend and to fail
+on resume.
+
+`commit e79a10652bbd3 ("ACPI: x86: Force StorageD3Enable on more products") <https://git.kernel.org/torvalds/c/e79a10652bbd3>`_
+
+Spurious IRQ1
+-------------
+A number of Renoir, Lucienne, Cezanne, & Barcelo platforms have a
+platform firmware bug where IRQ1 is triggered during s0i3 resume.
+
+This was fixed in the platform firmware, but a number of systems didn't
+receive any more platform firmware updates.
+
+`commit 8e60615e89321 ("platform/x86/amd: pmc: Disable IRQ1 wakeup for RN/CZN") <https://git.kernel.org/torvalds/c/8e60615e89321>`_
+
+Hardware timeout
+----------------
+The hardware performs many actions besides accepting the values from
+amd-pmc driver.  As the communication path with the hardware is a mailbox,
+it's possible that it might not respond quickly enough.
+This issue manifested as a failure to suspend: ::
+
+  PM: dpm_run_callback(): acpi_subsys_suspend_noirq+0x0/0x50 returns -110
+  amd_pmc AMDI0005:00: PM: failed to suspend noirq: error -110
+
+The timing problem was identified by comparing the values of the idle mask.
+
+`commit 3c3c8e88c8712 ("platform/x86: amd-pmc: Increase the response register timeout") <https://git.kernel.org/torvalds/c/3c3c8e88c8712>`_
+
+Failed to reach hardware sleep state with panel on
+--------------------------------------------------
+On some Strix systems certain panels were observed to block the system from
+entering a hardware sleep state if the internal panel was on during the sequence.
+
+Even though the panel got turned off during suspend it exposed a timing problem
+where an interrupt caused the display hardware to wake up and block low power
+state entry.
+
+`commit 40b8c14936bd2 ("drm/amd/display: Disable unneeded hpd interrupts during dm_init") <https://git.kernel.org/torvalds/c/40b8c14936bd2>`_
+
+Runtime power consumption issues
+================================
+Runtime power consumption is influenced by many factors, including but not
+limited to the configuration of the PCIe Active State Power Management (ASPM),
+the display brightness, the EPP policy of the CPU, and the power management
+of the devices.
+
+ASPM
+----
+For the best runtime power consumption, ASPM should be programmed as intended
+by the BIOS from the hardware vendor.  To accomplish this the Linux kernel
+should be compiled with ``CONFIG_PCIEASPM_DEFAULT`` set to ``y`` and the
+sysfs file ``/sys/module/pcie_aspm/parameters/policy`` should not be modified.
+
+Most notably, if L1.2 is not configured properly for any devices, the SoC
+will not be able to enter the deepest idle state.
+
+EPP Policy
+----------
+The ``energy_performance_preference`` sysfs file can be used to set a bias
+of efficiency or performance for a CPU.  This has a direct relationship on
+the battery life when more heavily biased towards performance.
+
+
+BIOS debug messages
+===================
+Most OEM machines don't have a serial UART for outputting kernel or BIOS
+debug messages. However BIOS debug messages are useful for understanding
+both BIOS bugs and bugs with the Linux kernel drivers that call BIOS AML.
+
+As the BIOS on most OEM AMD systems are based off an AMD reference BIOS,
+the infrastructure used for exporting debugging messages is often the same
+as AMD reference BIOS.
+
+Manually Parsing
+----------------
+There is generally an ACPI method ``\M460`` that different paths of the AML
+will call to emit a message to the BIOS serial log. This method takes
+7 arguments, with the first being a string and the rest being optional
+integers::
+
+  Method (M460, 7, Serialized)
+
+Here is an example of a string that BIOS AML may call out using ``\M460``::
+
+  M460 ("  OEM-ASL-PCIe Address (0x%X)._REG (%d %d)  PCSA = %d\n", DADR, Arg0, Arg1, PCSA, Zero, Zero)
+
+Normally when executed, the ``\M460`` method would populate the additional
+arguments into the string.  In order to get these messages from the Linux
+kernel a hook has been added into ACPICA that can capture the *arguments*
+sent to ``\M460`` and print them to the kernel ring buffer.
+For example the following message could be emitted into kernel ring buffer::
+
+  extrace-0174 ex_trace_args         :  "  OEM-ASL-PCIe Address (0x%X)._REG (%d %d)  PCSA = %d\n", ec106000, 2, 1, 1, 0, 0
+
+In order to get these messages, you need to compile with ``CONFIG_ACPI_DEBUG``
+and then turn on the following ACPICA tracing parameters.
+This can be done either on the kernel command line or at runtime:
+
+* ``acpi.trace_method_name=\M460``
+* ``acpi.trace_state=method``
+
+NOTE: These can be very noisy at bootup. If you turn these parameters on
+the kernel command, please also consider turning up ``CONFIG_LOG_BUF_SHIFT``
+to a larger size such as 17 to avoid losing early boot messages.
+
+Tool assisted Parsing
+---------------------
+As mentioned above, parsing by hand can be tedious, especially with a lot of
+messages.  To help with this, a tool has been created at
+`amd-debug-tools <https://git.kernel.org/pub/scm/linux/kernel/git/superm1/amd-debug-tools.git/about/>`_
+to help parse the messages.

Documentation/arch/x86/index.rst

@@ -25,6 +25,7 @@ x86-specific Documentation
    shstk
    iommu
    intel_txt
+   amd-debugging
    amd-memory-encryption
    amd_hsmp
    tdx