PM / Domains: Add support for removing nested PM domains by provider

If a device supports PM domains that are subdomains of another PM
domain, then the PM domains should be removed in reverse order to
ensure that the subdomains are removed first. Furthermore, if there is
more than one provider, then there needs to be a way to remove the
domains in reverse order for a specific provider.

Add the function of_genpd_remove_last() to remove the last PM domain
added by a given PM domain provider and return the generic_pm_domain
structure for the PM domain that was removed.

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

drivers/base/power/domain.c

@@ -1744,6 +1744,41 @@ out:
 }
 EXPORT_SYMBOL_GPL(of_genpd_add_subdomain);
 
+/**
+ * of_genpd_remove_last - Remove the last PM domain registered for a provider
+ * @provider: Pointer to device structure associated with provider
+ *
+ * Find the last PM domain that was added by a particular provider and
+ * remove this PM domain from the list of PM domains. The provider is
+ * identified by the 'provider' device structure that is passed. The PM
+ * domain will only be removed, if the provider associated with domain
+ * has been removed.
+ *
+ * Returns a valid pointer to struct generic_pm_domain on success or
+ * ERR_PTR() on failure.
+ */
+struct generic_pm_domain *of_genpd_remove_last(struct device_node *np)
+{
+	struct generic_pm_domain *gpd, *genpd = ERR_PTR(-ENOENT);
+	int ret;
+
+	if (IS_ERR_OR_NULL(np))
+		return ERR_PTR(-EINVAL);
+
+	mutex_lock(&gpd_list_lock);
+	list_for_each_entry(gpd, &gpd_list, gpd_list_node) {
+		if (gpd->provider == &np->fwnode) {
+			ret = genpd_remove(gpd);
+			genpd = ret ? ERR_PTR(ret) : gpd;
+			break;
+		}
+	}
+	mutex_unlock(&gpd_list_lock);
+
+	return genpd;
+}
+EXPORT_SYMBOL_GPL(of_genpd_remove_last);
+
 /**
  * genpd_dev_pm_detach - Detach a device from its PM domain.
  * @dev: Device to detach.

include/linux/pm_domain.h

@@ -204,6 +204,7 @@ extern int of_genpd_add_device(struct of_phandle_args *args,
 			       struct device *dev);
 extern int of_genpd_add_subdomain(struct of_phandle_args *parent,
 				  struct of_phandle_args *new_subdomain);
+extern struct generic_pm_domain *of_genpd_remove_last(struct device_node *np);
 
 int genpd_dev_pm_attach(struct device *dev);
 #else /* !CONFIG_PM_GENERIC_DOMAINS_OF */
@@ -237,6 +238,12 @@ static inline int genpd_dev_pm_attach(struct device *dev)
 {
 	return -ENODEV;
 }
+
+static inline
+struct generic_pm_domain *of_genpd_remove_last(struct device_node *np)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
 #endif /* CONFIG_PM_GENERIC_DOMAINS_OF */
 
 #ifdef CONFIG_PM