powerpc/smp: Implement cpu_to_coregroup_id

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.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200810071834.92514-11-srikar@linux.vnet.ibm.com

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index dfebca9..b725fb6 100644 (file)
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1247,6 +1247,26 @@ 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);
 }