[PATCH v4 4/5] x86/amd_node: Skip SMN setup on Hygon Fam18h models 0x04-0x08

[Lin Wang]

amd_smn_init() distributes host bridge roots according to
amd_num_nodes() and PCI enumeration order. Hygon Fam18h models
0x04-0x08 have multiple DF nodes per socket and group SMN roots by
socket, so the AMD mapping cannot provide their node-to-root map.

Leave the roots unclaimed on these models regardless of
CONFIG_HYGON_NODE; the AMD mapping does not apply to their topology.
Since amd_num_nodes() is independent of the root array, check
smn_exclusive before indexing the array so AMD SMN calls return
-ENODEV while its setup is inactive. When built, the Hygon node layer
provides the node-to-root mapping. Other Hygon models keep the existing
AMD SMN setup. amd_smn_init() can become AMD-only after the remaining
Hygon callers have moved to Hygon-specific interfaces.

Signed-off-by: Lin Wang <wanglin@xxxxxxxxxxxxxx>
---
 arch/x86/kernel/amd_node.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
index 0be01725a2a4..a0cfd74ada03 100644
--- a/arch/x86/kernel/amd_node.c
+++ b/arch/x86/kernel/amd_node.c
@@ -88,6 +88,9 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32 address, u32 *value, b
 	struct pci_dev *root;
 	int err = -ENODEV;
 
+	if (!smn_exclusive)
+		return err;
+
 	if (node >= amd_num_nodes())
 		return err;
 
@@ -95,9 +98,6 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32 address, u32 *value, b
 	if (!root)
 		return err;
 
-	if (!smn_exclusive)
-		return err;
-
 	guard(mutex)(&smn_mutex);
 
 	err = pci_write_config_dword(root, i_off, address);
@@ -252,6 +252,18 @@ static int __init amd_smn_init(void)
 	if (!cpu_feature_enabled(X86_FEATURE_ZEN))
 		return 0;
 
+	/*
+	 * Hygon models outside this range, including legacy parts, keep the
+	 * existing AMD SMN setup. Models 0x04-0x08 group SMN roots by socket
+	 * instead of amd_num_nodes(), so leave AMD SMN inactive. The Hygon node
+	 * layer, when built, owns their node-to-root mapping.
+	 */
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_HYGON &&
+	    boot_cpu_data.x86 == 0x18 &&
+	    boot_cpu_data.x86_model >= 0x04 &&
+	    boot_cpu_data.x86_model <= 0x08)
+		return 0;
+
 	guard(mutex)(&smn_mutex);
 
 	if (amd_roots)
-- 
2.43.0