serial: mxs-auart: fix the wrong RTS hardware flow control

Without checking if the auart supports the hardware flow control or not,
the old mxs_auart_set_mctrl() asserted the RTS pin blindly.

This will causes the auart receives wrong data in the following case:
   The far-end has already started the write operation, and wait for
the auart asserts the RTS pin. Then the auart starts the read operation,
but mxs_auart_set_mctrl() may be called before we set the RTSCTS in the
mxs_auart_settermios(). So the RTS pin is asserted in a wrong situation,
and we get the wrong data in the end.

This bug has been catched when I connect the mx23(DTE) to the mx53(DCE).

This patch also replaces the AUART_CTRL2_RTS with AUART_CTRL2_RTSEN.
We should use the real the hardware flow control, not the software-controled
hardware flow control.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 5 deletions

diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
index 2e341b81ff89..3a667eed63d6 100644
--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c
@@ -73,6 +73,7 @@
 #define AUART_CTRL0_CLKGATE                     (1 << 30)
 
 #define AUART_CTRL2_CTSEN                       (1 << 15)
+#define AUART_CTRL2_RTSEN                       (1 << 14)
 #define AUART_CTRL2_RTS                         (1 << 11)
 #define AUART_CTRL2_RXE                         (1 << 9)
 #define AUART_CTRL2_TXE                         (1 << 8)
@@ -259,9 +260,12 @@ static void mxs_auart_set_mctrl(struct uart_port *u, unsigned mctrl)
 
         u32 ctrl = readl(u->membase + AUART_CTRL2);
 
-        ctrl &= ~AUART_CTRL2_RTS;
-        if (mctrl & TIOCM_RTS)
-                ctrl |= AUART_CTRL2_RTS;
+        ctrl &= ~AUART_CTRL2_RTSEN;
+        if (mctrl & TIOCM_RTS) {
+                if (u->state->port.flags & ASYNC_CTS_FLOW)
+                        ctrl |= AUART_CTRL2_RTSEN;
+        }
+
         s->ctrl = mctrl;
         writel(ctrl, u->membase + AUART_CTRL2);
 }
@@ -359,9 +363,9 @@ static void mxs_auart_settermios(struct uart_port *u,
 
         /* figure out the hardware flow control settings */
         if (cflag & CRTSCTS)
-                ctrl2 |= AUART_CTRL2_CTSEN;
+                ctrl2 |= AUART_CTRL2_CTSEN | AUART_CTRL2_RTSEN;
         else
-                ctrl2 &= ~AUART_CTRL2_CTSEN;
+                ctrl2 &= ~(AUART_CTRL2_CTSEN | AUART_CTRL2_RTSEN);
 
         /* set baud rate */
         baud = uart_get_baud_rate(u, termios, old, 0, u->uartclk);