dm: core: Add a function to find the first inactive child

Some devices have children and want to press an existing inactive child
into service when needed. Add a function to help with this.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/core/device.c

@@ -681,6 +681,24 @@ int device_find_next_child(struct udevice **devp)
 	return 0;
 }
 
+int device_find_first_inactive_child(struct udevice *parent,
+				     enum uclass_id uclass_id,
+				     struct udevice **devp)
+{
+	struct udevice *dev;
+
+	*devp = NULL;
+	list_for_each_entry(dev, &parent->child_head, sibling_node) {
+		if (!device_active(dev) &&
+		    device_get_uclass_id(dev) == uclass_id) {
+			*devp = dev;
+			return 0;
+		}
+	}
+
+	return -ENODEV;
+}
+
 struct udevice *dev_get_parent(const struct udevice *child)
 {
 	return child->parent;

include/dm/device.h

@@ -519,6 +519,21 @@ int device_find_first_child(struct udevice *parent, struct udevice **devp);
  */
 int device_find_next_child(struct udevice **devp);
 
+/**
+ * device_find_first_inactive_child() - Find the first inactive child
+ *
+ * This is used to locate an existing child of a device which is of a given
+ * uclass.
+ *
+ * @parent:	Parent device to search
+ * @uclass_id:	Uclass to look for
+ * @devp:	Returns device found, if any
+ * @return 0 if found, else -ENODEV
+ */
+int device_find_first_inactive_child(struct udevice *parent,
+				     enum uclass_id uclass_id,
+				     struct udevice **devp);
+
 /**
  * device_has_children() - check if a device has any children
  *

test/dm/core.c

@@ -870,3 +870,34 @@ static int dm_test_uclass_names(struct unit_test_state *uts)
 	return 0;
 }
 DM_TEST(dm_test_uclass_names, DM_TESTF_SCAN_PDATA);
+
+static int dm_test_inactive_child(struct unit_test_state *uts)
+{
+	struct dm_test_state *dms = uts->priv;
+	struct udevice *parent, *dev1, *dev2;
+
+	/* Skip the behaviour in test_post_probe() */
+	dms->skip_post_probe = 1;
+
+	ut_assertok(uclass_first_device_err(UCLASS_TEST, &parent));
+
+	/*
+	 * Create a child but do not activate it. Calling the function again
+	 * should return the same child.
+	 */
+	ut_asserteq(-ENODEV, device_find_first_inactive_child(parent,
+							UCLASS_TEST, &dev1));
+	ut_assertok(device_bind_ofnode(parent, DM_GET_DRIVER(test_drv),
+				       "test_child", 0, ofnode_null(), &dev1));
+
+	ut_assertok(device_find_first_inactive_child(parent, UCLASS_TEST,
+						     &dev2));
+	ut_asserteq_ptr(dev1, dev2);
+
+	ut_assertok(device_probe(dev1));
+	ut_asserteq(-ENODEV, device_find_first_inactive_child(parent,
+							UCLASS_TEST, &dev2));
+
+	return 0;
+}
+DM_TEST(dm_test_inactive_child, DM_TESTF_SCAN_PDATA);