[PATCH] ARM: 2654/1: i.MX UART initialization sets and honors UFCR value

Patch from Sascha Hauer

This patch adds UCFR_RFDIV setting into i.MX serial driver.
This is required, if loader does not fully agree with Linux kernel
about UART setup manner. Linux only blindly expected some values until
now. This should enable to use even serial ports not recognized by
boot-loader as for example third UART found in the bluethoot module.
Patch also enables to detect original setup baudrate in more cases.

Signed-off-by: Pavel Pisa
Signed-off-by: Sascha Hauer
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

drivers/serial/imx.c

@@ -321,18 +321,39 @@ static void imx_break_ctl(struct uart_port *port, int break_state)
 #define TXTL 2 /* reset default */
 #define RXTL 1 /* reset default */
 
+static int imx_setup_ufcr(struct imx_port *sport, unsigned int mode)
+{
+	unsigned int val;
+	unsigned int ufcr_rfdiv;
+
+	/* set receiver / transmitter trigger level.
+	 * RFDIV is set such way to satisfy requested uartclk value
+	 */
+	val = TXTL<<10 | RXTL;
+	ufcr_rfdiv = (imx_get_perclk1() + sport->port.uartclk / 2) / sport->port.uartclk;
+
+	if(!ufcr_rfdiv)
+		ufcr_rfdiv = 1;
+
+	if(ufcr_rfdiv >= 7)
+		ufcr_rfdiv = 6;
+	else
+		ufcr_rfdiv = 6 - ufcr_rfdiv;
+
+	val |= UFCR_RFDIV & (ufcr_rfdiv << 7);
+
+	UFCR((u32)sport->port.membase) = val;
+
+	return 0;
+}
+
 static int imx_startup(struct uart_port *port)
 {
 	struct imx_port *sport = (struct imx_port *)port;
 	int retval;
-	unsigned int val;
 	unsigned long flags;
 
-	/* set receiver / transmitter trigger level. We assume
-	 * that RFDIV has been set by the arch setup or by the bootloader.
-	 */
-	val = (UFCR((u32)sport->port.membase) & UFCR_RFDIV)  | TXTL<<10 | RXTL;
-	UFCR((u32)sport->port.membase) = val;
+	imx_setup_ufcr(sport, 0);
 
 	/* disable the DREN bit (Data Ready interrupt enable) before
 	 * requesting IRQs
@@ -737,9 +758,12 @@ static void __init
 imx_console_get_options(struct imx_port *sport, int *baud,
 			   int *parity, int *bits)
 {
+
 	if ( UCR1((u32)sport->port.membase) | UCR1_UARTEN ) {
 		/* ok, the port was enabled */
 		unsigned int ucr2, ubir,ubmr, uartclk;
+		unsigned int baud_raw;
+		unsigned int ucfr_rfdiv;
 
 		ucr2 = UCR2((u32)sport->port.membase);
 
@@ -758,9 +782,35 @@ imx_console_get_options(struct imx_port *sport, int *baud,
 
 		ubir = UBIR((u32)sport->port.membase) & 0xffff;
 		ubmr = UBMR((u32)sport->port.membase) & 0xffff;
-		uartclk = sport->port.uartclk;
 
-		*baud = ((uartclk/16) * (ubir + 1)) / (ubmr + 1);
+
+		ucfr_rfdiv = (UFCR((u32)sport->port.membase) & UFCR_RFDIV) >> 7;
+		if (ucfr_rfdiv == 6)
+			ucfr_rfdiv = 7;
+		else
+			ucfr_rfdiv = 6 - ucfr_rfdiv;
+
+		uartclk = imx_get_perclk1();
+		uartclk /= ucfr_rfdiv;
+
+		{	/*
+			 * The next code provides exact computation of
+			 *   baud_raw = round(((uartclk/16) * (ubir + 1)) / (ubmr + 1))
+			 * without need of float support or long long division,
+			 * which would be required to prevent 32bit arithmetic overflow
+			 */
+			unsigned int mul = ubir + 1;
+			unsigned int div = 16 * (ubmr + 1);
+			unsigned int rem = uartclk % div;
+
+			baud_raw = (uartclk / div) * mul;
+			baud_raw += (rem * mul + div / 2) / div;
+			*baud = (baud_raw + 50) / 100 * 100;
+		}
+
+		if(*baud != baud_raw)
+			printk(KERN_INFO "Serial: Console IMX rounded baud rate from %d to %d\n",
+				baud_raw, *baud);
 	}
 }
 
@@ -787,6 +837,8 @@ imx_console_setup(struct console *co, char *options)
 	else
 		imx_console_get_options(sport, &baud, &parity, &bits);
 
+	imx_setup_ufcr(sport, 0);
+
 	return uart_set_options(&sport->port, co, baud, parity, bits, flow);
 }