[S] Change in coreboot[main]: drivers/uart/sifive.c: Fix divisor calculation

[Maximilian Brune (Code Review)]

Maximilian Brune has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/79951?usp=email )

Change subject: drivers/uart/sifive.c: Fix divisor calculation
......................................................................

drivers/uart/sifive.c: Fix divisor calculation

The divisor is calculated using the following formula:
div = (frequency / baudrate) - 1;

The current implementation however essentially cacluates:
div = (frequency / baudrate);

Signed-off-by: Maximilian Brune 
Change-Id: I8a0898ce9016a70c0f91dc8a99fc1cf9e46d20c4
---
M src/drivers/uart/sifive.c
1 file changed, 8 insertions(+), 3 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/51/79951/1

diff --git a/src/drivers/uart/sifive.c b/src/drivers/uart/sifive.c
index d1b89dc..68759c8 100644
--- a/src/drivers/uart/sifive.c
+++ b/src/drivers/uart/sifive.c
@@ -47,9 +47,14 @@

void uart_init(unsigned int idx)
 {
-	unsigned int div;
-	div = uart_baudrate_divisor(get_uart_baudrate(),
-		uart_platform_refclk(), uart_input_clock_divider());
+	// according to FU740 manual:
+	// f_baud = f_in / (div + 1)
+	// <=>
+	// div = (f_in / f_baud) - 1
+	unsigned int div = uart_baudrate_divisor(get_uart_baudrate(), uart_platform_refclk(),
+			uart_input_clock_divider());
+	div -= 1;
+
    sifive_uart_init(uart_platform_baseptr(idx), div);
 }