serial: omap: unlock the port lock

This patch unlocks the port lock before calling a serial_core API
and re-acquires the port lock after calling it.
This patch fixes a system freeze issue seen when the serial_core
API uart_write_wakeup() eventually attempts to acquire the port lock
already acquired by omap serial interrupt handler.

Tested-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Ruchika Kharwar <ruchika@ti.com>
Signed-off-by: Pavan Savoy <pavan_savoy@ti.com>
Signed-off-by: Vijay Badawadagi <bvijay@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index d244163c99db..9e4419ca3028 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -224,8 +224,11 @@ static void transmit_chars(struct uart_omap_port *up, unsigned int lsr)
                         break;
         } while (--count > 0);
 
-        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) {
+                spin_unlock(&up->port.lock);
                 uart_write_wakeup(&up->port);
+                spin_lock(&up->port.lock);
+        }
 
         if (uart_circ_empty(xmit))
                 serial_omap_stop_tx(&up->port);