uart8250: Fix and unify baudrate divisor calculation

Divisor is a function of requested baudrate, platform-specific
reference clock and amount of oversampling done on the UART reference.
Calculate this parameter with divisor rounded to nearest integer.

When building without option_table or when there is no entry for
baud_rate, CONFIG_TTYS0_BAUD is used for default baudrate.

For OxPCIe use of 4 MHz for reference was arbitrary giving correct
divisor for 115200 but somewhat inaccurate for lower baudrates.
Actual hardware is 62500000 with 16 times oversampling.

FIXME: Field for baudrate in lb_tables is still incorrect.

Change-Id: I68539738469af780fadd3392263dd9b3d5964d2d
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/5229
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

2 files changed, 10 insertions, 49 deletions

diff --git a/src/lib/uart8250.c b/src/lib/uart8250.c
index c9075a227a..d136eb8867 100644
--- a/src/lib/uart8250.c
+++ b/src/lib/uart8250.c
@@ -21,15 +21,16 @@
 #include <arch/io.h>
 #include <uart.h>
 #include <uart8250.h>
-#include <pc80/mc146818rtc.h>
 #include <trace.h>
 
-#if CONFIG_USE_OPTION_TABLE
-#include "option_table.h"
-#endif
-
 /* Should support 8250, 16450, 16550, 16550A type UARTs */
 
+/* Nominal values only, good for the range of choices Kconfig offers for
+ * set of standard baudrates.
+ */
+#define BAUDRATE_REFCLK		(115200)
+#define BAUDRATE_OVERSAMPLE	(1)
+
 /* Expected character delay at 1200bps is 9ms for a working UART
  * and no flow-control. Assume UART as stuck if shift register
  * or FIFO takes more than 50ms per character to appear empty.
@@ -108,26 +109,8 @@ void uart8250_init(unsigned base_port, unsigned divisor)
 
 void uart_init(void)
 {
-	/* TODO the divisor calculation is hard coded to standard UARTs. Some
-	 * UARTs won't work with these values. This should be a property of the
-	 * UART used, worst case a Kconfig variable. For now live with hard
-	 * codes as the only devices that might be different are the iWave
-	 * iRainbowG6 and the OXPCIe952 card (and the latter is memory mapped)
-	 */
-	unsigned int div = (115200 / CONFIG_TTYS0_BAUD);
-
-#if !defined(__SMM__) && CONFIG_USE_OPTION_TABLE
-	static const unsigned char divisor[8] = { 1, 2, 3, 6, 12, 24, 48, 96 };
-	unsigned b_index = 0;
-#if defined(__PRE_RAM__)
-	b_index = read_option(baud_rate, 0);
-	b_index &= 7;
-	div = divisor[b_index];
-#else
-	if (get_option(&b_index, "baud_rate") == CB_SUCCESS)
-		div = divisor[b_index];
-#endif
-#endif
-
+	unsigned int div;
+	div = uart_baudrate_divisor(default_baudrate(), BAUDRATE_REFCLK,
+		BAUDRATE_OVERSAMPLE);
 	uart8250_init(CONFIG_TTYS0_BASE, div);
 }
diff --git a/src/lib/uart8250mem.c b/src/lib/uart8250mem.c
index 040e732df3..5e96825834 100644
--- a/src/lib/uart8250mem.c
+++ b/src/lib/uart8250mem.c
@@ -21,10 +21,6 @@
 #include <arch/io.h>
 #include <uart.h>
 #include <uart8250.h>
-#include <pc80/mc146818rtc.h>
-#if CONFIG_USE_OPTION_TABLE
-#include "option_table.h"
-#endif
 #include <device/device.h>
 #include <delay.h>
 
@@ -96,7 +92,6 @@ void uart8250_mem_init(unsigned base_port, unsigned divisor)
 	/* DLAB on */
 	write8(base_port + UART_LCR, UART_LCR_DLAB | CONFIG_TTYS0_LCS);
 
-	/* Set Baud Rate Divisor. 12 ==> 9600 Baud */
 	write8(base_port + UART_DLL, divisor & 0xFF);
 	write8(base_port + UART_DLM, (divisor >> 8) & 0xFF);
 
@@ -106,27 +101,11 @@ void uart8250_mem_init(unsigned base_port, unsigned divisor)
 
 u32 uart_mem_init(void)
 {
-	unsigned uart_baud = CONFIG_TTYS0_BAUD;
 	u32 uart_bar = 0;
 	unsigned div;
 
-	/* find out the correct baud rate */
-#if !defined(__SMM__) && CONFIG_USE_OPTION_TABLE
-	static const unsigned baud[8] = { 115200, 57600, 38400, 19200, 9600, 4800, 2400, 1200 };
-	unsigned b_index = 0;
-#if defined(__PRE_RAM__)
-	b_index = read_option(baud_rate, 0);
-	b_index &= 7;
-	uart_baud = baud[b_index];
-#else
-	if (get_option(&b_index, "baud_rate") == CB_SUCCESS)
-		uart_baud = baud[b_index];
-#endif
-#endif
-
 	/* Now find the UART base address and calculate the divisor */
 #if CONFIG_DRIVERS_OXFORD_OXPCIE
-
 #if defined(MORE_TESTING) && !defined(__SIMPLE_DEVICE__)
 	device_t dev = dev_find_device(0x1415, 0xc158, NULL);
 	if (!dev)
@@ -145,10 +124,9 @@ u32 uart_mem_init(void)
 #endif
 	uart_bar = CONFIG_OXFORD_OXPCIE_BASE_ADDRESS + 0x1000; // 1st UART
 	// uart_bar = CONFIG_OXFORD_OXPCIE_BASE_ADDRESS + 0x2000; // 2nd UART
-
-	div = 4000000 / uart_baud;
 #endif
 
+	div = uart_baudrate_divisor(default_baudrate(), uart_platform_refclk(), 16);
 	if (uart_bar)
 		uart8250_mem_init(uart_bar, div);