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>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/drivers/oxford/oxpcie/oxpcie_early.c b/src/drivers/oxford/oxpcie/oxpcie_early.c
index d04e9d4df0..4f6f9649f5 100644
--- a/src/drivers/oxford/oxpcie/oxpcie_early.c
+++ b/src/drivers/oxford/oxpcie/oxpcie_early.c
@@ -21,6 +21,7 @@
 #include <arch/io.h>
 #include <arch/early_variables.h>
 #include <delay.h>
+#include <uart.h>
 #include <uart8250.h>
 #include <device/pci_def.h>
 
@@ -116,7 +117,14 @@ void oxford_init(void)
 	/* Now the UART initialization */
 	u32 uart0_base = CONFIG_OXFORD_OXPCIE_BASE_ADDRESS + 0x1000;
 
-	uart8250_mem_init(uart0_base, (4000000 / CONFIG_TTYS0_BAUD));
+	unsigned int div = uart_baudrate_divisor(default_baudrate(),
+		uart_platform_refclk(), 16);
+	uart8250_mem_init(uart0_base, div);
 }
 
 #endif
+
+unsigned int uart_platform_refclk(void)
+{
+	return 62500000;
+}