[PATCH 4/4] lib: utils/serial: Ensure baudrate is non-zero before using

[Andrew Jones <ajones@ventanamicro.com>]

RISC-V doesn't generate exceptions on divide-by-zero, but the result,
all bits set, is not likely what people expect either. In all cases
where we divide by baudrate there's a chance it's zero (when the DT
it came from is "bad"). To avoid difficult to debug situations, leave
baudrate dependent registers alone when baudrate is zero, as, also in
all cases, it appears we can skip initialization of those registers
and still [hopefully] have a functioning UART.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
---
 lib/utils/serial/gaisler-uart.c | 2 +-
 lib/utils/serial/shakti-uart.c  | 8 ++++++--
 lib/utils/serial/sifive-uart.c  | 2 +-
 lib/utils/serial/uart8250.c     | 7 +++++--
 4 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/lib/utils/serial/gaisler-uart.c b/lib/utils/serial/gaisler-uart.c
index 5f30ee43b719..eec75cca0c98 100644
--- a/lib/utils/serial/gaisler-uart.c
+++ b/lib/utils/serial/gaisler-uart.c
@@ -70,7 +70,7 @@ int gaisler_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
 	uart_base = (volatile char *)base;
 
 	/* Configure baudrate */
-	if (in_freq)
+	if (in_freq && baudrate)
 		set_reg(UART_REG_SCALER, in_freq / (baudrate * 8 + 7));
 
 	ctrl = get_reg(UART_REG_CTRL);
diff --git a/lib/utils/serial/shakti-uart.c b/lib/utils/serial/shakti-uart.c
index 5f2fe75c9f33..2f09f141b9cf 100644
--- a/lib/utils/serial/shakti-uart.c
+++ b/lib/utils/serial/shakti-uart.c
@@ -47,8 +47,12 @@ static struct sbi_console_device shakti_console = {
 int shakti_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
 {
 	uart_base = (volatile char *)base;
-	u16 baud = (u16)(in_freq/(16 * baudrate));
-	writew(baud, uart_base + REG_BAUD);
+	u16 baud;
+
+	if (baudrate) {
+		baud = (u16)(in_freq / (16 * baudrate));
+		writew(baud, uart_base + REG_BAUD);
+	}
 
 	sbi_console_set_device(&shakti_console);
 
diff --git a/lib/utils/serial/sifive-uart.c b/lib/utils/serial/sifive-uart.c
index 7078611a5274..3581d47a6d4b 100644
--- a/lib/utils/serial/sifive-uart.c
+++ b/lib/utils/serial/sifive-uart.c
@@ -97,7 +97,7 @@ int sifive_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
 	uart_baudrate = baudrate;
 
 	/* Configure baudrate */
-	if (in_freq)
+	if (in_freq && baudrate)
 		set_reg(UART_REG_DIV, uart_min_clk_divisor(in_freq, baudrate));
 
 	/* Disable interrupts */
diff --git a/lib/utils/serial/uart8250.c b/lib/utils/serial/uart8250.c
index 38ea11af4d31..99bf1bf733f2 100644
--- a/lib/utils/serial/uart8250.c
+++ b/lib/utils/serial/uart8250.c
@@ -93,7 +93,7 @@ static struct sbi_console_device uart8250_console = {
 int uart8250_init(unsigned long base, u32 in_freq, u32 baudrate, u32 reg_shift,
 		  u32 reg_width, u32 reg_offset)
 {
-	u16 bdiv;
+	u16 bdiv = 0;
 
 	uart8250_base      = (volatile char *)base + reg_offset;
 	uart8250_reg_shift = reg_shift;
@@ -101,7 +101,10 @@ int uart8250_init(unsigned long base, u32 in_freq, u32 baudrate, u32 reg_shift,
 	uart8250_in_freq   = in_freq;
 	uart8250_baudrate  = baudrate;
 
-	bdiv = (uart8250_in_freq + 8 * uart8250_baudrate) / (16 * uart8250_baudrate);
+	if (uart8250_baudrate) {
+		bdiv = (uart8250_in_freq + 8 * uart8250_baudrate) /
+		       (16 * uart8250_baudrate);
+	}
 
 	/* Disable all interrupts */
 	set_reg(UART_IER_OFFSET, 0x00);
-- 
2.36.1