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, 108 insertions, 0 deletions

diff --git a/Documentation/driver-api/soundwire/locking.rst b/Documentation/driver-api/soundwire/locking.rst
new file mode 100644
index 000000000..3a7ffb3d8
--- /dev/null
+++ b/Documentation/driver-api/soundwire/locking.rst
@@ -0,0 +1,108 @@
+=================
+SoundWire Locking
+=================
+
+This document explains locking mechanism of the SoundWire Bus. Bus uses
+following locks in order to avoid race conditions in Bus operations on
+shared resources.
+
+  - Bus lock
+
+  - Message lock
+
+Bus lock
+========
+
+SoundWire Bus lock is a mutex and is part of Bus data structure
+(sdw_bus) which is used for every Bus instance. This lock is used to
+serialize each of the following operations(s) within SoundWire Bus instance.
+
+  - Addition and removal of Slave(s), changing Slave status.
+
+  - Prepare, Enable, Disable and De-prepare stream operations.
+
+  - Access of Stream data structure.
+
+Message lock
+============
+
+SoundWire message transfer lock. This mutex is part of
+Bus data structure (sdw_bus). This lock is used to serialize the message
+transfers (read/write) within a SoundWire Bus instance.
+
+Below examples show how locks are acquired.
+
+Example 1
+---------
+
+Message transfer.
+
+  1. For every message transfer
+
+     a. Acquire Message lock.
+
+     b. Transfer message (Read/Write) to Slave1 or broadcast message on
+        Bus in case of bank switch.
+
+     c. Release Message lock
+
+     ::
+
+	+----------+                    +---------+
+	|          |                    |         |
+	|   Bus    |                    | Master  |
+	|          |                    | Driver  |
+	|          |                    |         |
+	+----+-----+                    +----+----+
+	     |                               |
+	     |     bus->ops->xfer_msg()      |
+	     <-------------------------------+   a. Acquire Message lock
+	     |                               |   b. Transfer message
+	     |                               |
+	     +------------------------------->   c. Release Message lock
+	     |    return success/error       |   d. Return success/error
+	     |                               |
+	     +                               +
+
+Example 2
+---------
+
+Prepare operation.
+
+  1. Acquire lock for Bus instance associated with Master 1.
+
+  2. For every message transfer in Prepare operation
+
+     a. Acquire Message lock.
+
+     b. Transfer message (Read/Write) to Slave1 or broadcast message on
+        Bus in case of bank switch.
+
+     c. Release Message lock.
+
+  3. Release lock for Bus instance associated with Master 1 ::
+
+	+----------+                    +---------+
+	|          |                    |         |
+	|   Bus    |                    | Master  |
+	|          |                    | Driver  |
+	|          |                    |         |
+	+----+-----+                    +----+----+
+	     |                               |
+	     |    sdw_prepare_stream()       |
+	     <-------------------------------+   1. Acquire bus lock
+	     |                               |   2. Perform stream prepare
+	     |                               |
+	     |                               |
+	     |     bus->ops->xfer_msg()      |
+	     <-------------------------------+   a. Acquire Message lock
+	     |                               |   b. Transfer message
+	     |                               |
+	     +------------------------------->   c. Release Message lock
+	     |    return success/error       |   d. Return success/error
+	     |                               |
+	     |                               |
+	     |    return success/error       |   3. Release bus lock
+	     +------------------------------->   4. Return success/error
+	     |                               |
+	     +                               +