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 <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/platforms/pseries/pseries_energy.c

···
 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;
···
 	/* 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++) {
 
···
 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;
···
 	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++) {