interconnect: Add helpers for enabling/disabling a path

There is a repeated pattern in multiple drivers where they want to switch
the bandwidth between zero and some other value. This is happening often
in the suspend/resume callbacks. Let's add helper functions to enable and
disable the path, so that callers don't have to take care of remembering
the bandwidth values and handle this in the framework instead.

With this patch the users can call icc_disable() and icc_enable() to lower
their bandwidth request to zero and then restore it back to it's previous
value.

Suggested-by: Evan Green <[e-mail]>
Suggested-by: Bjorn Andersson <[e-mail]>
Signed-off-by: Georgi Djakov <[e-mail]>
Reviewed-by: Matthias Kaehlcke <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Georgi Djakov <[e-mail]>

drivers/interconnect/core.c

···
 		hlist_add_head(&path->reqs[i].req_node, &node->req_list);
 		path->reqs[i].node = node;
 		path->reqs[i].dev = dev;
+		path->reqs[i].enabled = true;
 		/* reference to previous node was saved during path traversal */
 		node = node->reverse;
 	}
···
 	if (p->pre_aggregate)
 		p->pre_aggregate(node);
 
-	hlist_for_each_entry(r, &node->req_list, req_node)
+	hlist_for_each_entry(r, &node->req_list, req_node) {
+		if (!r->enabled)
+			continue;
 		p->aggregate(node, r->tag, r->avg_bw, r->peak_bw,
 			     &node->avg_bw, &node->peak_bw);
+	}
 
 	return 0;
 }
···
 	return ret;
 }
 EXPORT_SYMBOL_GPL(icc_set_bw);
+
+static int __icc_enable(struct icc_path *path, bool enable)
+{
+	int i;
+
+	if (!path)
+		return 0;
+
+	if (WARN_ON(IS_ERR(path) || !path->num_nodes))
+		return -EINVAL;
+
+	mutex_lock(&icc_lock);
+
+	for (i = 0; i < path->num_nodes; i++)
+		path->reqs[i].enabled = enable;
+
+	mutex_unlock(&icc_lock);
+
+	return icc_set_bw(path, path->reqs[0].avg_bw,
+			  path->reqs[0].peak_bw);
+}
+
+int icc_enable(struct icc_path *path)
+{
+	return __icc_enable(path, true);
+}
+EXPORT_SYMBOL_GPL(icc_enable);
+
+int icc_disable(struct icc_path *path)
+{
+	return __icc_enable(path, false);
+}
+EXPORT_SYMBOL_GPL(icc_disable);
 
 /**
  * icc_get() - return a handle for path between two endpoints

drivers/interconnect/internal.h

···
  * @req_node: entry in list of requests for the particular @node
  * @node: the interconnect node to which this constraint applies
  * @dev: reference to the device that sets the constraints
+ * @enabled: indicates whether the path with this request is enabled
  * @tag: path tag (optional)
  * @avg_bw: an integer describing the average bandwidth in kBps
  * @peak_bw: an integer describing the peak bandwidth in kBps
···
 	struct hlist_node req_node;
 	struct icc_node *node;
 	struct device *dev;
+	bool enabled;
 	u32 tag;
 	u32 avg_bw;
 	u32 peak_bw;

include/linux/interconnect.h

···
 struct icc_path *of_icc_get(struct device *dev, const char *name);
 struct icc_path *devm_of_icc_get(struct device *dev, const char *name);
 void icc_put(struct icc_path *path);
+int icc_enable(struct icc_path *path);
+int icc_disable(struct icc_path *path);
 int icc_set_bw(struct icc_path *path, u32 avg_bw, u32 peak_bw);
 void icc_set_tag(struct icc_path *path, u32 tag);
 
···
 
 static inline void icc_put(struct icc_path *path)
 {
+}
+
+static inline int icc_enable(struct icc_path *path)
+{
+	return 0;
+}
+
+static inline int icc_disable(struct icc_path *path)
+{
+	return 0;
 }
 
 static inline int icc_set_bw(struct icc_path *path, u32 avg_bw, u32 peak_bw)