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>
4da22f1418