serial: 8250_fintek: Add using BIOS IRQ default setting

In 8250_fintek.c probe_setup_port(), we'll detect the IRQ trigger mode by
irq_get_irq_data() and pass it to fintek_8250_set_irq_mode(). If detected
Edge mode, we'll set the UART with Edge/High mode, otherwise Level/Low.

But in some motherboard, The APIC maybe setting to Level/High. In this case
the driver will setting wrong configuration into UART. So we add a option
to kernel parameter to control the driver as following:

	fintek_uart_irq_mode_override= [SERIAL]
		{default, bios}
		If the parameter is "default", the driver will using
		former IRQ override methed(By IRQ trigger type).
		otherwise, we'll don't change the UART IRQ setting.

Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>

drivers/tty/serial/8250/8250_fintek.c

@@ -92,13 +92,34 @@
 #define F81866_UART_CLK_18_432MHZ BIT(0)
 #define F81866_UART_CLK_24MHZ BIT(1)
 
+#define FINTEK_IRQ_MODE_BY_DETECT	0
+#define FINTEK_IRQ_MODE_BY_BIOS		1
+
 struct fintek_8250 {
 	u16 pid;
 	u16 base_port;
 	u8 index;
 	u8 key;
 };
 
+static int not_override_irq_mode = FINTEK_IRQ_MODE_BY_DETECT;
+
+static int __init parse_uart_irq_mode_override(char *arg)
+{
+	if (!arg)
+		return -EINVAL;
+
+	if (strcmp(arg, "bios") == 0)
+		not_override_irq_mode = FINTEK_IRQ_MODE_BY_BIOS;
+	else if (strcmp(arg, "default") == 0)
+		not_override_irq_mode = FINTEK_IRQ_MODE_BY_DETECT;
+	else
+		return -EINVAL;
+
+	return 0;
+}
+early_param("fintek_uart_irq_mode_override", parse_uart_irq_mode_override);
+
 static u8 sio_read_reg(struct fintek_8250 *pdata, u8 reg)
 {
 	outb(reg, pdata->base_port + ADDR_PORT);
@@ -234,6 +255,12 @@ static int fintek_8250_rs485_config(struct uart_port *port, struct ktermios *ter
 
 static void fintek_8250_set_irq_mode(struct fintek_8250 *pdata, bool is_level)
 {
+	if (not_override_irq_mode == FINTEK_IRQ_MODE_BY_BIOS) {
+		pr_info("Fintek UART(%04x) irq mode is using BIOS default",
+				pdata->pid);
+		return;
+	}
+
 	sio_write_reg(pdata, LDN, pdata->index);
 
 	switch (pdata->pid) {