serial: pl011: set UART011_CR_RXE in pl011_set_termios after port shutdown

UART011_CR_RXE is set in pl011_startup() during normal initialization, and
cleared by pl011_disable_uart() during port shutdown.

You can use a none-console port in poll mode like kgdboc does with
tty_find_polling_driver() after a port shutdown. But pl011_startup() is not
called in tty_find_polling_driver(). So you need to set UART011_CR_RXE to
reenable receive function.

Not sure setting UART011_CR_RXE in pl011_set_termios() is a good idea
through.

Signed-off-by: Hongyu Xie <xiehongyu1@kylinos.cn>
Link: https://lore.kernel.org/r/20230501070909.1144547-1-xiehongyu1@kylinos.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -2166,6 +2166,13 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
 	 * ----------^----------^----------^----------^-----
 	 */
 	pl011_write_lcr_h(uap, lcr_h);
+
+	/*
+	 * Receive was disabled by pl011_disable_uart during shutdown.
+	 * Need to reenable receive if you need to use a tty_driver
+	 * returns from tty_find_polling_driver() after a port shutdown.
+	 */
+	old_cr |= UART011_CR_RXE;
 	pl011_write(old_cr, uap, REG_CR);
 
 	spin_unlock_irqrestore(&port->lock, flags);