Lookup the coregroup id from the associativity array.

If unable to detect the coregroup id, fallback on the core id.
This way, ensure sched_domain degenerates and an extra sched domain is
not created.

Ideally this function should have been implemented in
arch/powerpc/kernel/smp.c. However if its implemented in mm/numa.c, we
don't need to find the primary domain again.

If the device-tree mentions more than one coregroup, then kernel
implements only the last or the smallest coregroup, which currently
corresponds to the penultimate domain in the device-tree.

Cc: linuxppc-dev <redacted>
Cc: LKML <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Anton Blanchard <redacted>
Cc: Oliver O'Halloran <oohall@gmail.com>
Cc: Nathan Lynch <redacted>
Cc: Michael Neuling <redacted>
Cc: Gautham R Shenoy <redacted>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <redacted>
Cc: Jordan Niethe <redacted>
Reviewed-by : Gautham R. Shenoy [off-list ref]
Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog v1 -> v2:
	Move coregroup_enabled before getting associativity (Gautham)

 arch/powerpc/mm/numa.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 0d57779e7942..8b3b3ec7fcc4 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -1218,6 +1218,26 @@ int find_and_online_cpu_nid(int cpu)
 
 int cpu_to_coregroup_id(int cpu)
 {
+	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};
+	int index;
+
+	if (cpu < 0 || cpu > nr_cpu_ids)
+		return -1;
+
+	if (!coregroup_enabled)
+		goto out;
+
+	if (!firmware_has_feature(FW_FEATURE_VPHN))
+		goto out;
+
+	if (vphn_get_associativity(cpu, associativity))
+		goto out;
+
+	index = of_read_number(associativity, 1);
+	if (index > min_common_depth + 1)
+		return of_read_number(&associativity[index - 1], 1);
+
+out:
 	return cpu_to_core_id(cpu);
 }
 

-- 
2.17.1