serial: imx.c: fix CTS trigger level lower to avoid lost chars

commit 1c5250d6163dac28be3afabdfb6c723f107051b7 upstream.

The imx CTS trigger level is left at its reset value that is 32
chars. Since the RX FIFO has 32 entries, when CTS is raised, the
FIFO already is full. However, some serial port devices first empty
their TX FIFO before stopping when CTS is raised, resulting in lost
chars.

This patch sets the trigger level lower so that other chars arrive
after CTS is raised, there is still room for 16 of them.

Signed-off-by: Valentin Longchamp<valentin.longchamp@epfl.ch>
Tested-by: Philippe Rétornaz<philippe.retornaz@epfl.ch>
Acked-by: Wolfram Sang<w.sang@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/serial/imx.c b/drivers/serial/imx.c
index d00fcf8e6c70e0a68318da2a4ac83c1f29cc48a0..fd6b1352b2d7b44b7a1461f4c709d6df4e6b07d2 100644 (file)
--- a/drivers/serial/imx.c
+++ b/drivers/serial/imx.c
@@ -119,7 +119,8 @@
 #define  MX2_UCR3_RXDMUXSEL     (1<<2)  /* RXD Muxed Input Select, on mx2/mx3 */
 #define  UCR3_INVT      (1<<1)  /* Inverted Infrared transmission */
 #define  UCR3_BPEN      (1<<0)  /* Preset registers enable */
-#define  UCR4_CTSTL_32   (32<<10) /* CTS trigger level (32 chars) */
+#define  UCR4_CTSTL_SHF  10      /* CTS trigger level shift */
+#define  UCR4_CTSTL_MASK 0x3F    /* CTS trigger is 6 bits wide */
 #define  UCR4_INVR      (1<<9)  /* Inverted infrared reception */
 #define  UCR4_ENIRI     (1<<8)  /* Serial infrared interrupt enable */
 #define  UCR4_WKEN      (1<<7)  /* Wake interrupt enable */
@@ -590,6 +591,9 @@ static int imx_setup_ufcr(struct imx_port *sport, unsigned int mode)
        return 0;
 }
 
+/* half the RX buffer size */
+#define CTSTL 16
+
 static int imx_startup(struct uart_port *port)
 {
        struct imx_port *sport = (struct imx_port *)port;
@@ -606,6 +610,10 @@ static int imx_startup(struct uart_port *port)
        if (USE_IRDA(sport))
                temp |= UCR4_IRSC;
 
+       /* set the trigger level for CTS */
+       temp &= ~(UCR4_CTSTL_MASK<<  UCR4_CTSTL_SHF);
+       temp |= CTSTL<<  UCR4_CTSTL_SHF;
+
        writel(temp & ~UCR4_DREN, sport->port.membase + UCR4);
 
        if (USE_IRDA(sport)) {