[PATCH] serial: imx: Fix buggy transmissions when baudrate mismatches

[Fabio Estevam]

Bit 7 of UCR3 is described in the i.MX reference manuals (with the exception
of i.MX1) as follows:

ADNIMP: Autobaud Detection Not Improved-. Disables new features of
	autobaud detection (See Baud Rate Automatic Detection
	Protocol, for more details).

	0 Autobaud detection new features selected
	1 Keep old autobaud detection mechanism

The "new features" mechanism occasionally causes the receiver to get out of sync 
and continuously produces received characters of '0xff'.

In order to reproduce the problem:

$ cs0.baudrate=19200
- Change the terminal baudrate to 19200
- Type in the console and it should look good
- Change the terminal baudrate back to 115200
- Type 'b' in the console, then a stream of '0xff' is transmitted in loop

Setting the ADNIMP bit avoids the transmission of '0xff' in loop.

Also rename the bit definition as per the reference manual.

Tested on mx6q.

Based on a patch from Eric Nelson for U-boot.

Signed-off-by: Fabio Estevam <fabio.estevam at freescale.com>
---
As the 0xff character is not seen in the console, an easy way to 'see' it is 
doing like this in order to easily demonstrate the bug:

--- a/drivers/serial/serial_imx.c
+++ b/drivers/serial/serial_imx.c
@@ -258,7 +258,8 @@ static int imx_serial_getc(struct console_device *cdev)
        while (readl(priv->regs + priv->devtype->uts) & UTS_RXEMPTY);
 
        ch = readl(priv->regs + URXD0);
-
+       if (ch >= 0x80)
+               ch = '?';
        return ch;
 }

 drivers/serial/serial_imx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/serial/serial_imx.c b/drivers/serial/serial_imx.c
index e0bd185..cb10627 100644
--- a/drivers/serial/serial_imx.c
+++ b/drivers/serial/serial_imx.c
@@ -79,7 +79,7 @@
 #define  UCR3_DSR        (1<<10) /* Data set ready */
 #define  UCR3_DCD        (1<<9)  /* Data carrier detect */
 #define  UCR3_RI         (1<<8)  /* Ring indicator */
-#define  UCR3_TIMEOUTEN  (1<<7)  /* Timeout interrupt enable */
+#define  UCR3_ADNIMP     (1<<7)  /* Autobaud Detection Not Improved */
 #define  UCR3_RXDSEN	 (1<<6)  /* Receive status interrupt enable */
 #define  UCR3_AIRINTEN   (1<<5)  /* Async IR wake interrupt enable */
 #define  UCR3_AWAKEN	 (1<<4)  /* Async wake interrupt enable */
@@ -152,7 +152,7 @@ static struct imx_serial_devtype_data imx1_data = {
 
 static struct imx_serial_devtype_data imx21_data = {
 	.ucr1_val = 0,
-	.ucr3_val = 0x700 | UCR3_RXDMUXSEL,
+	.ucr3_val = 0x700 | UCR3_RXDMUXSEL | UCR3_ADNIMP,
 	.ucr4_val = UCR4_CTSTL_32,
 	.uts = 0xb4,
 	.onems = 0xb0,
-- 
1.8.3.2