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>
diff --git a/src/lib/uart8250.c b/src/lib/uart8250.c
index c9075a2..d136eb8 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 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);
}