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, 48 insertions, 0 deletions

diff --git a/Documentation/driver-api/i2c.rst b/Documentation/driver-api/i2c.rst
new file mode 100644
index 000000000..7582c079d
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+++ b/Documentation/driver-api/i2c.rst
@@ -0,0 +1,48 @@
+I\ :sup:`2`\ C and SMBus Subsystem
+==================================
+
+I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for
+the "Inter-IC" bus, a simple bus protocol which is widely used where low
+data rate communications suffice. Since it's also a licensed trademark,
+some vendors use another name (such as "Two-Wire Interface", TWI) for
+the same bus. I2C only needs two signals (SCL for clock, SDA for data),
+conserving board real estate and minimizing signal quality issues. Most
+I2C devices use seven bit addresses, and bus speeds of up to 400 kHz;
+there's a high speed extension (3.4 MHz) that's not yet found wide use.
+I2C is a multi-master bus; open drain signaling is used to arbitrate
+between masters, as well as to handshake and to synchronize clocks from
+slower clients.
+
+The Linux I2C programming interfaces support the master side of bus
+interactions and the slave side. The programming interface is
+structured around two kinds of driver, and two kinds of device. An I2C
+"Adapter Driver" abstracts the controller hardware; it binds to a
+physical device (perhaps a PCI device or platform_device) and exposes a
+:c:type:`struct i2c_adapter <i2c_adapter>` representing each
+I2C bus segment it manages. On each I2C bus segment will be I2C devices
+represented by a :c:type:`struct i2c_client <i2c_client>`.
+Those devices will be bound to a :c:type:`struct i2c_driver
+<i2c_driver>`, which should follow the standard Linux driver model. There
+are functions to perform various I2C protocol operations; at this writing
+all such functions are usable only from task context.
+
+The System Management Bus (SMBus) is a sibling protocol. Most SMBus
+systems are also I2C conformant. The electrical constraints are tighter
+for SMBus, and it standardizes particular protocol messages and idioms.
+Controllers that support I2C can also support most SMBus operations, but
+SMBus controllers don't support all the protocol options that an I2C
+controller will. There are functions to perform various SMBus protocol
+operations, either using I2C primitives or by issuing SMBus commands to
+i2c_adapter devices which don't support those I2C operations.
+
+.. kernel-doc:: include/linux/i2c.h
+   :internal:
+
+.. kernel-doc:: drivers/i2c/i2c-boardinfo.c
+   :functions: i2c_register_board_info
+
+.. kernel-doc:: drivers/i2c/i2c-core-base.c
+   :export:
+
+.. kernel-doc:: drivers/i2c/i2c-core-smbus.c
+   :export: