PM / Domains: Don't attach devices in genpd with multi PM domains

The power-domain DT property may now contain a list of PM domain
specifiers, which represents that a device are partitioned across multiple
PM domains. This leads to a new situation in genpd_dev_pm_attach(), as only
one PM domain can be attached per device.

To remain things simple for the most common configuration, when a single PM
domain is used, let's treat the multiple PM domain case as being specific.

In other words, let's change genpd_dev_pm_attach() to check for multiple PM
domains and prevent it from attach any PM domain for this case. Instead,
leave this to be managed separately, from following changes to genpd.

Suggested-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/domain.c

@@ -2229,10 +2229,10 @@ static void genpd_dev_pm_sync(struct device *dev)
  * attaches the device to retrieved pm_domain ops.
  *
  * Returns 1 on successfully attached PM domain, 0 when the device don't need a
- * PM domain or a negative error code in case of failures. Note that if a
- * power-domain exists for the device, but it cannot be found or turned on,
- * then return -EPROBE_DEFER to ensure that the device is not probed and to
- * re-try again later.
+ * PM domain or when multiple power-domains exists for it, else a negative error
+ * code. Note that if a power-domain exists for the device, but it cannot be
+ * found or turned on, then return -EPROBE_DEFER to ensure that the device is
+ * not probed and to re-try again later.
  */
 int genpd_dev_pm_attach(struct device *dev)
 {
@@ -2243,10 +2243,18 @@ int genpd_dev_pm_attach(struct device *dev)
 	if (!dev->of_node)
 		return 0;
 
+	/*
+	 * Devices with multiple PM domains must be attached separately, as we
+	 * can only attach one PM domain per device.
+	 */
+	if (of_count_phandle_with_args(dev->of_node, "power-domains",
+				       "#power-domain-cells") != 1)
+		return 0;
+
 	ret = of_parse_phandle_with_args(dev->of_node, "power-domains",
 					"#power-domain-cells", 0, &pd_args);
 	if (ret < 0)
-		return 0;
+		return ret;
 
 	mutex_lock(&gpd_list_lock);
 	pd = genpd_get_from_provider(&pd_args);