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

3 files changed, 167 insertions, 0 deletions

diff --git a/Documentation/gpu/dp-mst/topology-figure-1.dot b/Documentation/gpu/dp-mst/topology-figure-1.dot
new file mode 100644
index 000000000..157e17c7e
--- /dev/null
+++ b/Documentation/gpu/dp-mst/topology-figure-1.dot
@@ -0,0 +1,52 @@
+digraph T {
+    /* Make sure our payloads are always drawn below the driver node */
+    subgraph cluster_driver {
+        fillcolor = grey;
+        style = filled;
+        driver -> {payload1, payload2} [dir=none];
+    }
+
+    /* Driver malloc references */
+    edge [style=dashed];
+    driver -> port1;
+    driver -> port2;
+    driver -> port3:e;
+    driver -> port4;
+
+    payload1:s -> port1:e;
+    payload2:s -> port3:e;
+    edge [style=""];
+
+    subgraph cluster_topology {
+        label="Topology Manager";
+        labelloc=bottom;
+
+        /* Topology references */
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        port2 -> mstb3 -> {port3, port4};
+        port3 -> mstb4;
+
+        /* Malloc references */
+        edge [style=dashed;dir=back];
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        port2 -> mstb3 -> {port3, port4};
+        port3 -> mstb4;
+    }
+
+    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
+
+    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
+    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue];
+
+    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen;shape=oval];
+    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen;shape=oval];
+    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen;shape=oval];
+    mstb4 [label="MSTB #4";style=filled;fillcolor=palegreen;shape=oval];
+
+    port1 [label="Port #1";shape=oval];
+    port2 [label="Port #2";shape=oval];
+    port3 [label="Port #3";shape=oval];
+    port4 [label="Port #4";shape=oval];
+}
diff --git a/Documentation/gpu/dp-mst/topology-figure-2.dot b/Documentation/gpu/dp-mst/topology-figure-2.dot
new file mode 100644
index 000000000..4243dd173
--- /dev/null
+++ b/Documentation/gpu/dp-mst/topology-figure-2.dot
@@ -0,0 +1,56 @@
+digraph T {
+    /* Make sure our payloads are always drawn below the driver node */
+    subgraph cluster_driver {
+        fillcolor = grey;
+        style = filled;
+        driver -> {payload1, payload2} [dir=none];
+    }
+
+    /* Driver malloc references */
+    edge [style=dashed];
+    driver -> port1;
+    driver -> port2;
+    driver -> port3:e;
+    driver -> port4 [color=red];
+
+    payload1:s -> port1:e;
+    payload2:s -> port3:e;
+    edge [style=""];
+
+    subgraph cluster_topology {
+        label="Topology Manager";
+        labelloc=bottom;
+
+        /* Topology references */
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        edge [color=red];
+        port2 -> mstb3 -> {port3, port4};
+        port3 -> mstb4;
+        edge [color=""];
+
+        /* Malloc references */
+        edge [style=dashed;dir=back];
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        port2 -> mstb3 -> port3;
+        edge [color=red];
+        mstb3 -> port4;
+        port3 -> mstb4;
+    }
+
+    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen];
+    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen];
+    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen];
+    mstb4 [label="MSTB #4";style=filled;fillcolor=grey];
+
+    port1 [label="Port #1"];
+    port2 [label="Port #2"];
+    port3 [label="Port #3"];
+    port4 [label="Port #4";style=filled;fillcolor=grey];
+
+    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
+
+    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
+    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue];
+}
diff --git a/Documentation/gpu/dp-mst/topology-figure-3.dot b/Documentation/gpu/dp-mst/topology-figure-3.dot
new file mode 100644
index 000000000..6cd78d067
--- /dev/null
+++ b/Documentation/gpu/dp-mst/topology-figure-3.dot
@@ -0,0 +1,59 @@
+digraph T {
+    /* Make sure our payloads are always drawn below the driver node */
+    subgraph cluster_driver {
+        fillcolor = grey;
+        style = filled;
+        edge [dir=none];
+        driver -> payload1;
+        driver -> payload2 [penwidth=3];
+        edge [dir=""];
+    }
+
+    /* Driver malloc references */
+    edge [style=dashed];
+    driver -> port1;
+    driver -> port2;
+    driver -> port3:e;
+    driver -> port4 [color=grey];
+    payload1:s -> port1:e;
+    payload2:s -> port3:e [penwidth=3];
+    edge [style=""];
+
+    subgraph cluster_topology {
+        label="Topology Manager";
+        labelloc=bottom;
+
+        /* Topology references */
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        edge [color=grey];
+        port2 -> mstb3 -> {port3, port4};
+        port3 -> mstb4;
+        edge [color=""];
+
+        /* Malloc references */
+        edge [style=dashed;dir=back];
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        port2 -> mstb3 [penwidth=3];
+        mstb3 -> port3 [penwidth=3];
+        edge [color=grey];
+        mstb3 -> port4;
+        port3 -> mstb4;
+    }
+
+    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen];
+    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen];
+    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen;penwidth=3];
+    mstb4 [label="MSTB #4";style=filled;fillcolor=grey];
+
+    port1 [label="Port #1"];
+    port2 [label="Port #2";penwidth=5];
+    port3 [label="Port #3";penwidth=3];
+    port4 [label="Port #4";style=filled;fillcolor=grey];
+
+    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
+
+    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
+    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue;penwidth=3];
+}