[PATCH 04/25] tty: serial: ar933x: drop uart_port->lock before calling tty_flip_buffer_push()

[Viresh Kumar <viresh.kumar@linaro.org>]

The -rt patch triggers a lockdep warning for serial drivers if
tty_flip_buffer_push() is called with uart_port->lock locked. This never shows
up on UP kernels.

Release the port lock before calling tty_flip_buffer_push() and reacquire it
after the call.

Similar stuff was already done for few other drivers in the past, like:

commit 2389b272168ceec056ca1d8a870a97fa9c26e11a
Author: Thomas Gleixner <tglx@linutronix.de>
Date:   Tue May 29 21:53:50 2007 +0100

    [ARM] 4417/1: Serial: Fix AMBA drivers locking

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/tty/serial/ar933x_uart.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/serial/ar933x_uart.c b/drivers/tty/serial/ar933x_uart.c
index 27f20c5..964ca90 100644
--- a/drivers/tty/serial/ar933x_uart.c
+++ b/drivers/tty/serial/ar933x_uart.c
@@ -322,7 +322,9 @@ static void ar933x_uart_rx_chars(struct ar933x_uart_port *up)
 			tty_insert_flip_char(port, ch, TTY_NORMAL);
 	} while (max_count-- > 0);
 
+	spin_unlock(&up->port.lock);
 	tty_flip_buffer_push(port);
+	spin_lock(&up->port.lock);
 }
 
 static void ar933x_uart_tx_chars(struct ar933x_uart_port *up)
-- 
1.7.12.rc2.18.g61b472e