powerpc/pseries: Fix drc-info mappings of logical cpus to drc-index

There are a couple subtle errors in the mapping between cpu-ids and a
cpus associated drc-index when using the new ibm,drc-info property.

The first is that while drc-info may have been a supported firmware
feature at boot it is possible we have migrated to a CEC with older
firmware that doesn't support the ibm,drc-info property. In that case
the device tree would have been updated after migration to remove the
ibm,drc-info property and replace it with the older style ibm,drc-*
properties for types, indexes, names, and power-domains. PAPR even
goes as far as dictating that if we advertise support for drc-info
that we are capable of supporting either property type at runtime.

The second is that the first value of the ibm,drc-info property is
the int encoded count of drc-info entries. As such "value" returned
by of_prop_next_u32() is pointing at that count, and not the first
element of the first drc-info entry as is expected by the
of_read_drc_info_cell() helper.

Fix the first by ignoring DRC-INFO firmware feature and instead
testing directly for ibm,drc-info, and then falling back to the
old style ibm,drc-indexes in the case it doesn't exit.

Fix the second by incrementing value to the next element prior to
parsing drc-info entries.

Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1573449697-5448-3-git-send-email-tyreld@linux.ibm.com

diff --git a/arch/powerpc/platforms/pseries/pseries_energy.c b/arch/powerpc/platforms/pseries/pseries_energy.c
index a96874f..09e98d3 100644 (file)
--- a/arch/powerpc/platforms/pseries/pseries_energy.c
+++ b/arch/powerpc/platforms/pseries/pseries_energy.c
@@ -36,6 +36,7 @@ static int sysfs_entries;
 static u32 cpu_to_drc_index(int cpu)
 {
        struct device_node *dn = NULL;
+       struct property *info;
        int thread_index;
        int rc = 1;
        u32 ret = 0;
@@ -47,20 +48,18 @@ static u32 cpu_to_drc_index(int cpu)
        /* Convert logical cpu number to core number */
        thread_index = cpu_core_index_of_thread(cpu);
 
-       if (firmware_has_feature(FW_FEATURE_DRC_INFO)) {
-               struct property *info = NULL;
+       info = of_find_property(dn, "ibm,drc-info", NULL);
+       if (info) {
                struct of_drc_info drc;
                int j;
                u32 num_set_entries;
                const __be32 *value;
 
-               info = of_find_property(dn, "ibm,drc-info", NULL);
-               if (info == NULL)
-                       goto err_of_node_put;
-
                value = of_prop_next_u32(info, NULL, &num_set_entries);
                if (!value)
                        goto err_of_node_put;
+               else
+                       value++;
 
                for (j = 0; j < num_set_entries; j++) {
 
@@ -110,6 +109,7 @@ err:
 static int drc_index_to_cpu(u32 drc_index)
 {
        struct device_node *dn = NULL;
+       struct property *info;
        const int *indexes;
        int thread_index = 0, cpu = 0;
        int rc = 1;
@@ -117,21 +117,18 @@ static int drc_index_to_cpu(u32 drc_index)
        dn = of_find_node_by_path("/cpus");
        if (dn == NULL)
                goto err;
-
-       if (firmware_has_feature(FW_FEATURE_DRC_INFO)) {
-               struct property *info = NULL;
+       info = of_find_property(dn, "ibm,drc-info", NULL);
+       if (info) {
                struct of_drc_info drc;
                int j;
                u32 num_set_entries;
                const __be32 *value;
 
-               info = of_find_property(dn, "ibm,drc-info", NULL);
-               if (info == NULL)
-                       goto err_of_node_put;
-
                value = of_prop_next_u32(info, NULL, &num_set_entries);
                if (!value)
                        goto err_of_node_put;
+               else
+                       value++;
 
                for (j = 0; j < num_set_entries; j++) {