powerpc/papr_scm: Update the NUMA distance table for the target node

Platform device helper routines won't update the NUMA distance table
while creating a platform device, even if the device is present on a
NUMA node that doesn't have memory or CPU. This is especially true for
pmem devices. If the target node of the pmem device is not online, we
find the nearest online node to the device and associate the pmem device
with that online node. To find the nearest online node, we should have
the numa distance table updated correctly. Update the distance
information during the device probe.

For a papr scm device on NUMA node 3 distance_lookup_table value for
distance_ref_points_depth = 2 before and after fix is below:

Before fix:
  node 3 distance depth 0  - 0
  node 3 distance depth 1  - 0
  node 4 distance depth 0  - 4
  node 4 distance depth 1  - 2
  node 5 distance depth 0  - 5
  node 5 distance depth 1  - 1

After fix
  node 3 distance depth 0  - 3
  node 3 distance depth 1  - 1
  node 4 distance depth 0  - 4
  node 4 distance depth 1  - 2
  node 5 distance depth 0  - 5
  node 5 distance depth 1  - 1

Without the fix, the nearest numa node to the pmem device (NUMA node 3)
will be picked as 4. After the fix, we get the correct numa node which
is 5.

Fixes: da1115fd ("powerpc/nvdimm: Pick nearby online node if the device node is not online")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230404041433.1781804-1-aneesh.kumar@linux.ibm.com

arch/powerpc/mm/numa.c

@@ -366,6 +366,7 @@ void update_numa_distance(struct device_node *node)
 	WARN(numa_distance_table[nid][nid] == -1,
 	     "NUMA distance details for node %d not provided\n", nid);
 }
+EXPORT_SYMBOL_GPL(update_numa_distance);
 
 /*
  * ibm,numa-lookup-index-table= {N, domainid1, domainid2, ..... domainidN}

arch/powerpc/platforms/pseries/papr_scm.c

@@ -1428,6 +1428,13 @@ static int papr_scm_probe(struct platform_device *pdev)
 		return -ENODEV;
 	}
 
+	/*
+	 * open firmware platform device create won't update the NUMA 
+	 * distance table. For PAPR SCM devices we use numa_map_to_online_node()
+	 * to find the nearest online NUMA node and that requires correct
+	 * distance table information.
+	 */
+	update_numa_distance(dn);
 
 	p = kzalloc(sizeof(*p), GFP_KERNEL);
 	if (!p)