From: Andrei Simion <andreis@xilinx.com>
Date: Wed, 9 Nov 2011 02:16:51 +0000 (-0800)
Subject: Xilinx: ARM: Flexible baud rate calculation.
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=025346c3a3268af318aae925a617d49786a84756;p=thirdparty%2Fu-boot.git

Xilinx: ARM: Flexible baud rate calculation.

Values used in U-boot's baud rate calculation are chosen in such
a way to keep the error between the target and calculated baud
rate under 3%.

The header was changed to avoid hardcoding values such as the ones
used in the baud rate calculation. The UART input frequency uses
the value defined in 'xparameters.h'.
---

diff --git a/drivers/serial/serial_xpssuart.c b/drivers/serial/serial_xpssuart.c
index ad9428e1733..dffae7d1486 100644
--- a/drivers/serial/serial_xpssuart.c
+++ b/drivers/serial/serial_xpssuart.c
@@ -15,26 +15,38 @@ void serial_setbrg(void)
 	/*              master clock
 	 * Baud rate = ---------------
 	 *              bgen*(bdiv+1)
-	 *
-	 * master clock = 50MHz (I think?)
-	 * bdiv remains at default (reset) 15
-	 *
-	 * Simplify RHS to base/bgen, where base == master/16
 	 */
-	long base = XDFUART_BASECLK;
 	long baud = gd->baudrate;
-	long bgen = base / baud;
-	long base_err = base - (bgen*baud);
-	long mod_bgen = bgen + (base_err >= 0 ? 1 : -1);
-	long mod_err = base - (mod_bgen*baud);
 
-	/* you'd think there'd be an abs() macro somewhere in include/... */
-	mod_err = mod_err < 0 ? -mod_err : mod_err;
-	base_err = base_err < 0 ? -base_err : base_err;
+	/* Variables to vary. */
+	unsigned int bdiv, bgen;
 
-	bgen = mod_err < base_err ? mod_bgen : bgen;
+	/* Calculation results. */
+	long calc_baud = 0;
+	unsigned int calc_bauderror;
 
-	xdfuart_writel(BAUDDIV,XDFUART_BDIV); /* Ensure it's 15 */
+	/* Find acceptable values for baud generation. */
+	for (bdiv = 4; bdiv < 255; bdiv++) {
+
+		bgen = XDFUART_MASTER / (baud * (bdiv + 1));
+		if (bgen < 2 || bgen > 65535)
+			continue;
+
+		calc_baud = XDFUART_MASTER / (bgen * (bdiv + 1));
+
+		/* Use first calculated baudrate with an acceptable
+		 * (<3%) error.
+		 */
+		if (baud > calc_baud)
+			calc_bauderror = baud - calc_baud;
+		else
+			calc_bauderror = calc_baud - baud;
+		if ( ((calc_bauderror * 100) / baud) < 3 )
+			break;
+
+	}
+
+	xdfuart_writel(BAUDDIV,bdiv);
 	xdfuart_writel(BAUDGEN,bgen);
 }
 
diff --git a/drivers/serial/serial_xpssuart.h b/drivers/serial/serial_xpssuart.h
index 1b871411c8b..cd0295407d1 100644
--- a/drivers/serial/serial_xpssuart.h
+++ b/drivers/serial/serial_xpssuart.h
@@ -12,18 +12,15 @@
 #if defined(CONFIG_UART0)
 # define UART_ID   0
 # define UART_BASE XPSS_UART0_BASEADDR
+# define XDFUART_MASTER XPAR_XUARTPSS_0_CLOCK_HZ
 #elif defined(CONFIG_UART1)
 # define UART_ID   1
 # define UART_BASE XPSS_UART1_BASEADDR
+# define XDFUART_MASTER XPAR_XUARTPSS_1_CLOCK_HZ
 #else
 # error "Need to configure a UART (0 or 1)"
 #endif
 
-/* Some clock/baud constants */
-#define XDFUART_MASTER 50000000L /* Master clock source for UART */
-#define XDFUART_BDIV          15 /* Default/reset BDIV value */
-#define XDFUART_BASECLK 3125000L /* master/(bdiv+1) */
-
 /* UART register offsets */
 #define XDFUART_CR_OFFSET          0x00  /* Control Register [8:0] */
 #define XDFUART_MR_OFFSET          0x04  /* Mode Register [10:0] */