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, 90 insertions, 0 deletions

diff --git a/Documentation/driver-api/mtd/spi-intel.rst b/Documentation/driver-api/mtd/spi-intel.rst
new file mode 100644
index 000000000..df854f20e
--- /dev/null
+++ b/Documentation/driver-api/mtd/spi-intel.rst
@@ -0,0 +1,90 @@
+==============================
+Upgrading BIOS using spi-intel
+==============================
+
+Many Intel CPUs like Baytrail and Braswell include SPI serial flash host
+controller which is used to hold BIOS and other platform specific data.
+Since contents of the SPI serial flash is crucial for machine to function,
+it is typically protected by different hardware protection mechanisms to
+avoid accidental (or on purpose) overwrite of the content.
+
+Not all manufacturers protect the SPI serial flash, mainly because it
+allows upgrading the BIOS image directly from an OS.
+
+The spi-intel driver makes it possible to read and write the SPI serial
+flash, if certain protection bits are not set and locked. If it finds
+any of them set, the whole MTD device is made read-only to prevent
+partial overwrites. By default the driver exposes SPI serial flash
+contents as read-only but it can be changed from kernel command line,
+passing "spi_intel.writeable=1".
+
+Please keep in mind that overwriting the BIOS image on SPI serial flash
+might render the machine unbootable and requires special equipment like
+Dediprog to revive. You have been warned!
+
+Below are the steps how to upgrade MinnowBoard MAX BIOS directly from
+Linux.
+
+ 1) Download and extract the latest Minnowboard MAX BIOS SPI image
+    [1]. At the time writing this the latest image is v92.
+
+ 2) Install mtd-utils package [2]. We need this in order to erase the SPI
+    serial flash. Distros like Debian and Fedora have this prepackaged with
+    name "mtd-utils".
+
+ 3) Add "spi_intel.writeable=1" to the kernel command line and reboot
+    the board (you can also reload the driver passing "writeable=1" as
+    module parameter to modprobe).
+
+ 4) Once the board is up and running again, find the right MTD partition
+    (it is named as "BIOS")::
+
+	# cat /proc/mtd
+	dev:    size   erasesize  name
+	mtd0: 00800000 00001000 "BIOS"
+
+    So here it will be /dev/mtd0 but it may vary.
+
+ 5) Make backup of the existing image first::
+
+	# dd if=/dev/mtd0ro of=bios.bak
+	16384+0 records in
+	16384+0 records out
+	8388608 bytes (8.4 MB) copied, 10.0269 s, 837 kB/s
+
+ 6) Verify the backup::
+
+	# sha1sum /dev/mtd0ro bios.bak
+	fdbb011920572ca6c991377c4b418a0502668b73  /dev/mtd0ro
+	fdbb011920572ca6c991377c4b418a0502668b73  bios.bak
+
+    The SHA1 sums must match. Otherwise do not continue any further!
+
+ 7) Erase the SPI serial flash. After this step, do not reboot the
+    board! Otherwise it will not start anymore::
+
+	# flash_erase /dev/mtd0 0 0
+	Erasing 4 Kibyte @ 7ff000 -- 100 % complete
+
+ 8) Once completed without errors you can write the new BIOS image::
+
+    # dd if=MNW2MAX1.X64.0092.R01.1605221712.bin of=/dev/mtd0
+
+ 9) Verify that the new content of the SPI serial flash matches the new
+    BIOS image::
+
+	# sha1sum /dev/mtd0ro MNW2MAX1.X64.0092.R01.1605221712.bin
+	9b4df9e4be2057fceec3a5529ec3d950836c87a2  /dev/mtd0ro
+	9b4df9e4be2057fceec3a5529ec3d950836c87a2 MNW2MAX1.X64.0092.R01.1605221712.bin
+
+    The SHA1 sums should match.
+
+ 10) Now you can reboot your board and observe the new BIOS starting up
+     properly.
+
+References
+----------
+
+[1] https://firmware.intel.com/sites/default/files/MinnowBoard%2EMAX_%2EX64%2E92%2ER01%2Ezip
+
+[2] http://www.linux-mtd.infradead.org/