PM / Domains: Don't treat zero found compatible idle states as an error

Instead of returning -EINVAL from of_genpd_parse_idle_states() in case none
compatible states was found, let's return 0 to indicate success. Assign
also the out-parameter *states to NULL and *n to 0, to indicate to the
caller that zero states have been found/allocated.

This enables the caller of of_genpd_parse_idle_states() to easier act on
the returned error code.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/domain.c

@@ -2478,8 +2478,8 @@ static int genpd_iterate_idle_states(struct device_node *dn,
  *
  * Returns the device states parsed from the OF node. The memory for the states
  * is allocated by this function and is the responsibility of the caller to
- * free the memory after use. If no domain idle states is found it returns
- * -EINVAL and in case of errors, a negative error code.
+ * free the memory after use. If any or zero compatible domain idle states is
+ * found it returns 0 and in case of errors, a negative error code is returned.
  */
 int of_genpd_parse_idle_states(struct device_node *dn,
 			struct genpd_power_state **states, int *n)
@@ -2488,8 +2488,14 @@ int of_genpd_parse_idle_states(struct device_node *dn,
 	int ret;
 
 	ret = genpd_iterate_idle_states(dn, NULL);
-	if (ret <= 0)
-		return ret < 0 ? ret : -EINVAL;
+	if (ret < 0)
+		return ret;
+
+	if (!ret) {
+		*states = NULL;
+		*n = 0;
+		return 0;
+	}
 
 	st = kcalloc(ret, sizeof(*st), GFP_KERNEL);
 	if (!st)