dm: core: Add uclass_first_device_err() to return a valid device

A common pattern is to call uclass_first_device() and then check if it
actually returns a device. Add a new function which does this, returning
an error if there are no devices in that uclass.

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

drivers/core/uclass.c

@@ -401,6 +401,19 @@ int uclass_first_device(enum uclass_id id, struct udevice **devp)
 	return uclass_get_device_tail(dev, ret, devp);
 }
 
+int uclass_first_device_err(enum uclass_id id, struct udevice **devp)
+{
+	int ret;
+
+	ret = uclass_first_device(id, devp);
+	if (ret)
+		return ret;
+	else if (!*devp)
+		return -ENODEV;
+
+	return 0;
+}
+
 int uclass_next_device(struct udevice **devp)
 {
 	struct udevice *dev = *devp;

include/dm/uclass.h

@@ -200,10 +200,21 @@ int uclass_get_device_by_phandle(enum uclass_id id, struct udevice *parent,
  *
  * @id: Uclass ID to look up
  * @devp: Returns pointer to the first device in that uclass, or NULL if none
- * @return 0 if OK (found or not found), -1 on error
+ * @return 0 if OK (found or not found), other -ve on error
  */
 int uclass_first_device(enum uclass_id id, struct udevice **devp);
 
+/**
+ * uclass_first_device_err() - Get the first device in a uclass
+ *
+ * The device returned is probed if necessary, and ready for use
+ *
+ * @id: Uclass ID to look up
+ * @devp: Returns pointer to the first device in that uclass, or NULL if none
+ * @return 0 if found, -ENODEV if not found, other -ve on error
+ */
+int uclass_first_device_err(enum uclass_id id, struct udevice **devp);
+
 /**
  * uclass_next_device() - Get the next device in a uclass
  *
@@ -211,7 +222,7 @@ int uclass_first_device(enum uclass_id id, struct udevice **devp);
  *
  * @devp: On entry, pointer to device to lookup. On exit, returns pointer
  * to the next device in the same uclass, or NULL if none
- * @return 0 if OK (found or not found), -1 on error
+ * @return 0 if OK (found or not found), other -ve on error
  */
 int uclass_next_device(struct udevice **devp);