coresight: Control path with range

CPU PM notifiers need to control only part of a path instead of always
operating on the full path.

Add internal enable and disable helpers that take an inclusive node
range [from, to], validate that the requested nodes are ordered before
using them.

Update the existed coresight_{enable|disable}_path() interfaces as
full-path wrappers by passing the first and last path nodes. The helpers
coresight_path_{first|last}_node() are provided for conveniently
fetching the first and last nodes on the path.

In coresight_enable_path_from_to(), if a failure occurs at the last node
in the range, no device is actually enabled in this case, bail out
directly.

Tested-by: Jie Gan <jie.gan@oss.qualcomm.com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20260515-arm_coresight_path_power_management_improvement-v14-16-f88c4a3ecfe9@arm.com

drivers/hwtracing/coresight/coresight-core.c

@@ -62,6 +62,24 @@ static LIST_HEAD(coresight_dev_idx_list);
 
 static const struct cti_assoc_op *cti_assoc_ops;
 
+static struct coresight_node *
+coresight_path_first_node(struct coresight_path *path)
+{
+	if (list_empty(&path->path_list))
+		return NULL;
+
+	return list_first_entry(&path->path_list, struct coresight_node, link);
+}
+
+static struct coresight_node *
+coresight_path_last_node(struct coresight_path *path)
+{
+	if (list_empty(&path->path_list))
+		return NULL;
+
+	return list_last_entry(&path->path_list, struct coresight_node, link);
+}
+
 void coresight_set_cti_ops(const struct cti_assoc_op *cti_op)
 {
 	cti_assoc_ops = cti_op;
@@ -488,19 +506,41 @@ int coresight_resume_source(struct coresight_device *csdev)
 EXPORT_SYMBOL_GPL(coresight_resume_source);
 
 /*
- * coresight_disable_path_from : Disable components in the given path starting
- * from @nd in the list. If @nd is NULL, all the components, except the SOURCE
- * are disabled.
+ * Callers must fetch nodes from the path and pass @from and @to to the path
+ * enable/disable functions. Walk the path from @from to locate @to. If @to
+ * is found, it indicates @from and @to are in order. Otherwise, they are out
+ * of order.
  */
-static void coresight_disable_path_from(struct coresight_path *path,
-					struct coresight_node *nd)
+static bool coresight_path_nodes_in_order(struct coresight_path *path,
+					  struct coresight_node *from,
+					  struct coresight_node *to)
+{
+	struct coresight_node *nd;
+
+	if (WARN_ON_ONCE(!from || !to))
+		return false;
+
+	nd = from;
+	list_for_each_entry_from(nd, &path->path_list, link) {
+		if (nd == to)
+			return true;
+	}
+
+	return false;
+}
+
+static void coresight_disable_path_from_to(struct coresight_path *path,
+					   struct coresight_node *from,
+					   struct coresight_node *to)
 {
 	u32 type;
 	struct coresight_device *csdev, *parent, *child;
+	struct coresight_node *nd;
 
-	if (!nd)
-		nd = list_first_entry(&path->path_list, struct coresight_node, link);
+	if (!coresight_path_nodes_in_order(path, from, to))
+		return;
 
+	nd = from;
 	list_for_each_entry_from(nd, &path->path_list, link) {
 		csdev = nd->csdev;
 		type = csdev->type;
@@ -534,12 +574,18 @@ static void coresight_disable_path_from(struct coresight_path *path,
 
 		/* Disable all helpers adjacent along the path last */
 		coresight_disable_helpers(csdev, path);
+
+		/* Iterate up to and including @to */
+		if (nd == to)
+			break;
 	}
 }
 
 void coresight_disable_path(struct coresight_path *path)
 {
-	coresight_disable_path_from(path, NULL);
+	coresight_disable_path_from_to(path,
+				       coresight_path_first_node(path),
+				       coresight_path_last_node(path));
 }
 EXPORT_SYMBOL_GPL(coresight_disable_path);
 
@@ -572,16 +618,21 @@ static int coresight_enable_helpers(struct coresight_device *csdev,
 	return ret;
 }
 
-int coresight_enable_path(struct coresight_path *path, enum cs_mode mode)
+static int coresight_enable_path_from_to(struct coresight_path *path,
+					 enum cs_mode mode,
+					 struct coresight_node *from,
+					 struct coresight_node *to)
 {
 	int ret = 0;
 	u32 type;
 	struct coresight_node *nd;
 	struct coresight_device *csdev, *parent, *child;
-	struct coresight_device *source;
 
-	source = coresight_get_source(path);
-	list_for_each_entry_reverse(nd, &path->path_list, link) {
+	if (!coresight_path_nodes_in_order(path, from, to))
+		return -EINVAL;
+
+	nd = to;
+	list_for_each_entry_from_reverse(nd, &path->path_list, link) {
 		csdev = nd->csdev;
 		type = csdev->type;
 
@@ -620,7 +671,8 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode)
 		case CORESIGHT_DEV_TYPE_LINK:
 			parent = list_prev_entry(nd, link)->csdev;
 			child = list_next_entry(nd, link)->csdev;
-			ret = coresight_enable_link(csdev, parent, child, source);
+			ret = coresight_enable_link(csdev, parent, child,
+						    coresight_get_source(path));
 			if (ret)
 				goto err_disable_helpers;
 			break;
@@ -628,6 +680,10 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode)
 			ret = -EINVAL;
 			goto err_disable_helpers;
 		}
+
+		/* Iterate down to and including @from */
+		if (nd == from)
+			break;
 	}
 
 out:
@@ -635,12 +691,23 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode)
 err_disable_helpers:
 	coresight_disable_helpers(csdev, path);
 err_disable_path:
+	/* No device is actually enabled */
+	if (nd == to)
+		goto out;
+
 	/* Fetch the previous node, the last successfully enabled one */
 	nd = list_next_entry(nd, link);
-	coresight_disable_path_from(path, nd);
+	coresight_disable_path_from_to(path, nd, to);
 	goto out;
 }
 
+int coresight_enable_path(struct coresight_path *path, enum cs_mode mode)
+{
+	return coresight_enable_path_from_to(path, mode,
+					     coresight_path_first_node(path),
+					     coresight_path_last_node(path));
+}
+
 struct coresight_device *coresight_get_sink(struct coresight_path *path)
 {
 	struct coresight_device *csdev;