4 files changed, 18 insertions, 5 deletions

diff --git a/Documentation/devicetree/bindings/serial/of-serial.txt b/Documentation/devicetree/bindings/serial/of-serial.txt
index 1928a3e83cd0..77054772a8f4 100644
--- a/Documentation/devicetree/bindings/serial/of-serial.txt
+++ b/Documentation/devicetree/bindings/serial/of-serial.txt
@@ -37,6 +37,7 @@ Optional properties:
 - auto-flow-control: one way to enable automatic flow control support. The
   driver is allowed to detect support for the capability even without this
   property.
+- has-hw-flow-control: the hardware has flow control capability.
 
 Example:
 
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 111ee8acb07e..65556fc57d56 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -2333,9 +2333,11 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
          * the trigger, or the MCR RTS bit is cleared.  In the case where
          * the remote UART is not using CTS auto flow control, we must
          * have sufficient FIFO entries for the latency of the remote
-         * UART to respond.  IOW, at least 32 bytes of FIFO.
+         * UART to respond.  IOW, at least 32 bytes of FIFO. Also enable
+         * AFE if hw flow control is supported
          */
-        if (up->capabilities & UART_CAP_AFE && port->fifosize >= 32) {
+        if ((up->capabilities & UART_CAP_AFE && (port->fifosize >= 32)) ||
+            (port->flags & UPF_HARD_FLOW)) {
                 up->mcr &= ~UART_MCR_AFE;
                 if (termios->c_cflag & CRTSCTS)
                         up->mcr |= UART_MCR_AFE;
diff --git a/drivers/tty/serial/of_serial.c b/drivers/tty/serial/of_serial.c
index 99246606a256..77ec6a147522 100644
--- a/drivers/tty/serial/of_serial.c
+++ b/drivers/tty/serial/of_serial.c
@@ -182,6 +182,10 @@ static int of_platform_serial_probe(struct platform_device *ofdev)
                                           "auto-flow-control"))
                         port8250.capabilities |= UART_CAP_AFE;
 
+                if (of_property_read_bool(ofdev->dev.of_node,
+                                          "has-hw-flow-control"))
+                        port8250.port.flags |= UPF_HARD_FLOW;
+
                 ret = serial8250_register_8250_port(&port8250);
                 break;
         }
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 9a01ee4dda6d..fbf6c5ad222f 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -174,8 +174,12 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
                         if (tty->termios.c_cflag & CBAUD)
                                 uart_set_mctrl(uport, TIOCM_RTS | TIOCM_DTR);
                 }
-
-                if (tty_port_cts_enabled(port)) {
+                /*
+                 * if hw support flow control without software intervention,
+                 * then skip the below check
+                 */
+                if (tty_port_cts_enabled(port) &&
+                    !(uport->flags & UPF_HARD_FLOW)) {
                         spin_lock_irq(&uport->lock);
                         if (!(uport->ops->get_mctrl(uport) & TIOCM_CTS))
                                 tty->hw_stopped = 1;
@@ -2775,7 +2779,9 @@ void uart_handle_cts_change(struct uart_port *uport, unsigned int status)
 
         uport->icount.cts++;
 
-        if (tty_port_cts_enabled(port)) {
+        /* skip below code if the hw flow control is supported */
+        if (tty_port_cts_enabled(port) &&
+            !(uport->flags & UPF_HARD_FLOW)) {
                 if (tty->hw_stopped) {
                         if (status) {
                                 tty->hw_stopped = 0;