powercap/dtpm: Destroy hierarchy function

The hierarchy creation function exits but without a destroy hierarchy
function. Due to that, the modules creating the hierarchy can not be
unloaded properly because they don't have an exit callback.

Provide the dtpm_destroy_hierarchy() function to remove the previously
created hierarchy.

The function relies on all the release mechanisms implemented by the
underlying powercap framework.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20220130210210.549877-4-daniel.lezcano@linaro.org

drivers/powercap/dtpm.c

@@ -617,3 +617,46 @@ out_unlock:
 	return ret;
 }
 EXPORT_SYMBOL_GPL(dtpm_create_hierarchy);
+
+static void __dtpm_destroy_hierarchy(struct dtpm *dtpm)
+{
+	struct dtpm *child, *aux;
+
+	list_for_each_entry_safe(child, aux, &dtpm->children, sibling)
+		__dtpm_destroy_hierarchy(child);
+
+	/*
+	 * At this point, we know all children were removed from the
+	 * recursive call before
+	 */
+	dtpm_unregister(dtpm);
+}
+
+void dtpm_destroy_hierarchy(void)
+{
+	int i;
+
+	mutex_lock(&dtpm_lock);
+
+	if (!pct)
+		goto out_unlock;
+
+	__dtpm_destroy_hierarchy(root);
+	
+
+	for (i = 0; i < ARRAY_SIZE(dtpm_subsys); i++) {
+
+		if (!dtpm_subsys[i]->exit)
+			continue;
+
+		dtpm_subsys[i]->exit();
+	}
+
+	powercap_unregister_control_type(pct);
+
+	pct = NULL;
+
+out_unlock:
+	mutex_unlock(&dtpm_lock);
+}
+EXPORT_SYMBOL_GPL(dtpm_destroy_hierarchy);

include/linux/dtpm.h

@@ -37,6 +37,7 @@ struct device_node;
 struct dtpm_subsys_ops {
 	const char *name;
 	int (*init)(void);
+	void (*exit)(void);
 	int (*setup)(struct dtpm *, struct device_node *);
 };
 
@@ -67,4 +68,6 @@ void dtpm_unregister(struct dtpm *dtpm);
 int dtpm_register(const char *name, struct dtpm *dtpm, struct dtpm *parent);
 
 int dtpm_create_hierarchy(struct of_device_id *dtpm_match_table);
+
+void dtpm_destroy_hierarchy(void);
 #endif