serial: 8250_fintek: fix the mismatched IRQ mode

Some BIOS only use _OSI("Linux") to distinguish between Linux & Windows.
Apply Level/Low to UART trigger mode if Windows, Edge/High mode otherwise.
But since 2.6.23 the mainline kernel no longer returns true for
_OSI(“Linux”).

The default IRQ0~15 trigger mode in Linux is Edge/High mode without
ACPI MADT override. It mismatches IRQ mode and makes UART malfunctional on
such motherboard.

This patch will check the current IRQ mode and apply correct mode to UART.

The following link is F81216AD spec PDF:
http://html.alldatasheet.com/html-pdf/257956/FINTEK/F81216AD/5569/
25/F81216AD.html

LDN0~3
	70h: IRQ channel & Mode register
		Bit 6~5	:
			00	: Active low level mode
			01	: Active high edge mode
		Bit 4	: Sharing Flag (0: not share/1: share)
		Bit 3~0 : IRQ channel

Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -13,6 +13,7 @@
 #include <linux/pnp.h>
 #include <linux/kernel.h>
 #include <linux/serial_core.h>
+#include <linux/irq.h>
 #include  "8250.h"
 
 #define ADDR_PORT 0
@@ -30,6 +31,12 @@
 #define IO_ADDR2 0x60
 #define LDN 0x7
 
+#define IRQ_MODE	0x70
+#define IRQ_SHARE	BIT(4)
+#define IRQ_MODE_MASK	(BIT(6) | BIT(5))
+#define IRQ_LEVEL_LOW	0
+#define IRQ_EDGE_HIGH	BIT(5)
+
 #define RS485  0xF0
 #define RTS_INVERT BIT(5)
 #define RS485_URA BIT(4)
@@ -176,10 +183,37 @@ static int find_base_port(struct fintek_8250 *pdata, u16 io_address)
 	return -ENODEV;
 }
 
+static int fintek_8250_set_irq_mode(struct fintek_8250 *pdata, bool level_mode)
+{
+	int status;
+	u8 tmp;
+
+	status = fintek_8250_enter_key(pdata->base_port, pdata->key);
+	if (status)
+		return status;
+
+	outb(LDN, pdata->base_port + ADDR_PORT);
+	outb(pdata->index, pdata->base_port + DATA_PORT);
+
+	outb(IRQ_MODE, pdata->base_port + ADDR_PORT);
+	tmp = inb(pdata->base_port + DATA_PORT);
+
+	tmp &= ~IRQ_MODE_MASK;
+	tmp |= IRQ_SHARE;
+	if (!level_mode)
+		tmp |= IRQ_EDGE_HIGH;
+
+	outb(tmp, pdata->base_port + DATA_PORT);
+	fintek_8250_exit_key(pdata->base_port);
+	return 0;
+}
+
 int fintek_8250_probe(struct uart_8250_port *uart)
 {
 	struct fintek_8250 *pdata;
 	struct fintek_8250 probe_data;
+	struct irq_data *irq_data = irq_get_irq_data(uart->port.irq);
+	bool level_mode = irqd_is_level_type(irq_data);
 
 	if (find_base_port(&probe_data, uart->port.iobase))
 		return -ENODEV;
@@ -192,5 +226,5 @@ int fintek_8250_probe(struct uart_8250_port *uart)
 	uart->port.rs485_config = fintek_8250_rs485_config;
 	uart->port.private_data = pdata;
 
-	return 0;
+	return fintek_8250_set_irq_mode(pdata, level_mode);
 }