RAS/AMD/ATL: Add debug prints for DF register reads

The ATL will fail early if the DF register access fails due to missing
PCI IDs in the amd_nb code. There aren't any clear indicators on why the
ATL will fail to load in this case.

Add a couple of debug print statements to highlight reasons for failure.

A common scenario is missing support for new hardware. If the ATL fails
to load on a system, and there is interest to support it, then dynamic
debugging can be enabled to help find the cause for failure. If there is
no interest in supporting ATL on a new system, then these failures will
be silent.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20241021152158.2525669-1-yazen.ghannam@amd.com

Author: yghannam

drivers/ras/amd/atl/access.c

@@ -70,12 +70,16 @@ static int __df_indirect_read(u16 node, u8 func, u16 reg, u8 instance_id, u32 *l
 	u32 ficaa = 0;
 
 	node = get_accessible_node(node);
-	if (node >= amd_nb_num())
+	if (node >= amd_nb_num()) {
+		pr_debug("Node %u is out of bounds\n", node);
 		goto out;
+	}
 
 	F4 = node_to_amd_nb(node)->link;
-	if (!F4)
+	if (!F4) {
+		pr_debug("DF function 4 not found\n");
 		goto out;
+	}
 
 	/* Enable instance-specific access. */
 	if (instance_id != DF_BROADCAST) {