serial: 8250_fintek: fix the mismatched IRQ mode
authorJi-Ze Hong (Peter Hong) <hpeter@gmail.com>
Fri, 27 May 2016 02:02:51 +0000 (10:02 +0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sat, 25 Jun 2016 20:50:53 +0000 (13:50 -0700)
commit4da22f1418cb6f09e974499794db2f5e59fe8090
tree736e982532dc8d0dbd4d8716650432c62c607205
parent30743257f04d8ffa1d58aa5f68f2be84f4607103
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