+#else
+
+/* stubs */
+#define usbtty_getc() 0
+#define usbtty_putc(a)
+#define usbtty_puts(a)
+#define usbtty_tstc() 0
+
+#endif /* CONFIG_USB_TTY */
+
+struct udevice;
+
+/**
+ * struct struct dm_serial_ops - Driver model serial operations
+ *
+ * The uclass interface is implemented by all serial devices which use
+ * driver model.
+ */
+struct dm_serial_ops {
+ /**
+ * setbrg() - Set up the baud rate generator
+ *
+ * Adjust baud rate divisors to set up a new baud rate for this
+ * device. Not all devices will support all rates. If the rate
+ * cannot be supported, the driver is free to select the nearest
+ * available rate. or return -EINVAL if this is not possible.
+ *
+ * @dev: Device pointer
+ * @baudrate: New baud rate to use
+ * @return 0 if OK, -ve on error
+ */
+ int (*setbrg)(struct udevice *dev, int baudrate);
+ /**
+ * getc() - Read a character and return it
+ *
+ * If no character is available, this should return -EAGAIN without
+ * waiting.
+ *
+ * @dev: Device pointer
+ * @return character (0..255), -ve on error
+ */
+ int (*getc)(struct udevice *dev);
+ /**
+ * putc() - Write a character
+ *
+ * @dev: Device pointer
+ * @ch: character to write
+ * @return 0 if OK, -ve on error
+ */
+ int (*putc)(struct udevice *dev, const char ch);
+ /**
+ * pending() - Check if input/output characters are waiting
+ *
+ * This can be used to return an indication of the number of waiting
+ * characters if the driver knows this (e.g. by looking at the FIFO
+ * level). It is acceptable to return 1 if an indeterminant number
+ * of characters is waiting.
+ *
+ * This method is optional.
+ *
+ * @dev: Device pointer
+ * @input: true to check input characters, false for output
+ * @return number of waiting characters, 0 for none, -ve on error
+ */
+ int (*pending)(struct udevice *dev, bool input);
+ /**
+ * clear() - Clear the serial FIFOs/holding registers
+ *
+ * This method is optional.
+ *
+ * This quickly clears any input/output characters from the UART.
+ * If this is not possible, but characters still exist, then it
+ * is acceptable to return -EAGAIN (try again) or -EINVAL (not
+ * supported).
+ *
+ * @dev: Device pointer
+ * @return 0 if OK, -ve on error
+ */
+ int (*clear)(struct udevice *dev);
+#if CONFIG_POST & CONFIG_SYS_POST_UART
+ /**
+ * loop() - Control serial device loopback mode
+ *
+ * @dev: Device pointer
+ * @on: 1 to turn loopback on, 0 to turn if off
+ */
+ int (*loop)(struct udevice *dev, int on);