commit 5fe212364 causes division by zero with large bauds

[Felipe Balbi <balbi@ti.com>]

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Hi Alexey,

your commit 5fe212364 causes division by zero with any baud rate larger
than 3 Mbaud (IP supports up to 3686400).

Maybe this patch is all we need to get it fixed ? (untested)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 816d1a2..b50327f 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -240,8 +240,14 @@ serial_omap_baud_is_mode16(struct uart_port *port, unsigned int baud)
 {
 	unsigned int n13 = port->uartclk / (13 * baud);
 	unsigned int n16 = port->uartclk / (16 * baud);
-	int baudAbsDiff13 = baud - (port->uartclk / (13 * n13));
-	int baudAbsDiff16 = baud - (port->uartclk / (16 * n16));
+	int baudAbsDiff13 = 0;
+	int baudAbsDiff16 = 0;
+
+	if (n13)
+		baudAbsDiff13 = baud - (port->uartclk / (13 * n13));
+	if (n16)
+		baudAbsDiff16 = baud - (port->uartclk / (16 * n16));
+
 	if(baudAbsDiff13 < 0)
 		baudAbsDiff13 = -baudAbsDiff13;
 	if(baudAbsDiff16 < 0)

Another possibility would be to convert this into a lookup table (also
untested):

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 816d1a2..942d68e 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -224,6 +224,48 @@ static void serial_omap_enable_wakeup(struct uart_omap_port *up, bool enable)
 	pdata->enable_wakeup(up->dev, enable);
 }
 
+struct uart_omap_config {
+	unsigned int baud;
+	unsigned int oversampling;
+	unsigned int divisor;
+};
+
+static struct uart_omap_config omap_port_configs[] = {
+	{ .baud = 300,		.oversampling = 16,	.divisor = 10000, },
+	{ .baud = 300,		.oversampling = 16,	.divisor = 10000, },
+	{ .baud = 600,		.oversampling = 16,	.divisor = 5000, },
+	{ .baud = 1200,		.oversampling = 16,	.divisor = 2500, },
+	{ .baud = 2400,		.oversampling = 16,	.divisor = 1250, },
+	{ .baud = 4800,		.oversampling = 16,	.divisor = 625, },
+	{ .baud = 9600,		.oversampling = 16,	.divisor = 312, },
+	{ .baud = 14400,	.oversampling = 16,	.divisor = 208, },
+	{ .baud = 19200,	.oversampling = 16,	.divisor = 156, },
+	{ .baud = 28800,	.oversampling = 16,	.divisor = 704, },
+	{ .baud = 38400,	.oversampling = 16,	.divisor = 78, },
+	{ .baud = 57600,	.oversampling = 16,	.divisor = 52, },
+	{ .baud = 115200,	.oversampling = 16,	.divisor = 26, },
+	{ .baud = 230400,	.oversampling = 16,	.divisor = 13, },
+	{ .baud = 460800,	.oversampling = 13,	.divisor = 8, },
+	{ .baud = 921600,	.oversampling = 13,	.divisor = 4, },
+	{ .baud = 1843200,	.oversampling = 13,	.divisor = 2, },
+	{ .baud = 3000000,	.oversampling = 16,	.divisor = 1, },
+	{ .baud = 3686400,	.oversampling = 13,	.divisor = 1, },
+	{  } /* Terminating Entry */
+};
+
+static struct uart_omap_config *
+__serial_omap_get_config(struct uart_port *port, unsigned int baud)
+{
+	struct uart_omap_config *cfg = omap_port_configs;
+
+	while (cfg++) {
+		if (cfg->baud == baud)
+			return cfg;
+	}
+
+	return NULL;
+}
+
 /*
  * serial_omap_baud_is_mode16 - check if baud rate is MODE16X
  * @port: uart port info
@@ -238,16 +280,12 @@ static void serial_omap_enable_wakeup(struct uart_omap_port *up, bool enable)
 static bool
 serial_omap_baud_is_mode16(struct uart_port *port, unsigned int baud)
 {
-	unsigned int n13 = port->uartclk / (13 * baud);
-	unsigned int n16 = port->uartclk / (16 * baud);
-	int baudAbsDiff13 = baud - (port->uartclk / (13 * n13));
-	int baudAbsDiff16 = baud - (port->uartclk / (16 * n16));
-	if(baudAbsDiff13 < 0)
-		baudAbsDiff13 = -baudAbsDiff13;
-	if(baudAbsDiff16 < 0)
-		baudAbsDiff16 = -baudAbsDiff16;
-
-	return (baudAbsDiff13 > baudAbsDiff16);
+	struct uart_omap_config *cfg = __serial_omap_get_config(port, baud);
+
+	if (!cfg)
+		return -EINVAL;
+
+	return (cfg->oversampling == 16);
 }
 
 /*
@@ -258,13 +296,12 @@ serial_omap_baud_is_mode16(struct uart_port *port, unsigned int baud)
 static unsigned int
 serial_omap_get_divisor(struct uart_port *port, unsigned int baud)
 {
-	unsigned int divisor;
+	struct uart_omap_config *cfg = __serial_omap_get_config(port, baud);
 
-	if (!serial_omap_baud_is_mode16(port, baud))
-		divisor = 13;
-	else
-		divisor = 16;
-	return port->uartclk/(baud * divisor);
+	if (!cfg)
+		return -EINVAL;
+
+	return cfg->divisor;
 }
 
 static void serial_omap_enable_ms(struct uart_port *port)

-- 
balbi

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