x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

1 files changed, 95 insertions, 0 deletions

diff --git a/Documentation/driver-api/pwrseq.rst b/Documentation/driver-api/pwrseq.rst
new file mode 100644
index 000000000..e1056d141
--- /dev/null
+++ b/Documentation/driver-api/pwrseq.rst
@@ -0,0 +1,95 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+.. Copyright 2024 Linaro Ltd.
+
+====================
+Power Sequencing API
+====================
+
+:Author: Bartosz Golaszewski
+
+Introduction
+============
+
+This framework is designed to abstract complex power-up sequences that are
+shared between multiple logical devices in the Linux kernel.
+
+The intention is to allow consumers to obtain a power sequencing handle
+exposed by the power sequence provider and delegate the actual requesting and
+control of the underlying resources as well as to allow the provider to
+mitigate any potential conflicts between multiple users behind the scenes.
+
+Glossary
+--------
+
+The power sequencing API uses a number of terms specific to the subsystem:
+
+Unit
+
+    A unit is a discrete chunk of a power sequence. For instance one unit may
+    enable a set of regulators, another may enable a specific GPIO. Units can
+    define dependencies in the form of other units that must be enabled before
+    it itself can be.
+
+Target
+
+    A target is a set of units (composed of the "final" unit and its
+    dependencies) that a consumer selects by its name when requesting a handle
+    to the power sequencer. Via the dependency system, multiple targets may
+    share the same parts of a power sequence but ignore parts that are
+    irrelevant.
+
+Descriptor
+
+    A handle passed by the pwrseq core to every consumer that serves as the
+    entry point to the provider layer. It ensures coherence between different
+    users and keeps reference counting consistent.
+
+Consumer interface
+==================
+
+The consumer API is aimed to be as simple as possible. The driver interested in
+getting a descriptor from the power sequencer should call pwrseq_get() and
+specify the name of the target it wants to reach in the sequence after calling
+pwrseq_enable(). The descriptor can be released by calling pwrseq_put() and
+the consumer can request the powering down of its target with
+pwrseq_disable(). Note that there is no guarantee that pwrseq_disable()
+will have any effect as there may be multiple users of the underlying resources
+who may keep them active.
+
+Provider interface
+==================
+
+The provider API is admittedly not nearly as straightforward as the one for
+consumers but it makes up for it in flexibility.
+
+Each provider can logically split the power-up sequence into discrete chunks
+(units) and define their dependencies. They can then expose named targets that
+consumers may use as the final point in the sequence that they wish to reach.
+
+To that end the providers fill out a set of configuration structures and
+register with the pwrseq subsystem by calling pwrseq_device_register().
+
+Dynamic consumer matching
+-------------------------
+
+The main difference between pwrseq and other Linux kernel providers is the
+mechanism for dynamic matching of consumers and providers. Every power sequence
+provider driver must implement the `match()` callback and pass it to the pwrseq
+core when registering with the subsystems.
+
+When a client requests a sequencer handle, the core will call this callback for
+every registered provider and let it flexibly figure out whether the proposed
+client device is indeed its consumer. For example: if the provider binds to the
+device-tree node representing a power management unit of a chipset and the
+consumer driver controls one of its modules, the provider driver may parse the
+relevant regulator supply properties in device tree and see if they lead from
+the PMU to the consumer.
+
+API reference
+=============
+
+.. kernel-doc:: include/linux/pwrseq/provider.h
+   :internal:
+
+.. kernel-doc:: drivers/power/sequencing/core.c
+   :export: