Fix uart boot errors on M1000e blade chassis

Somebody else figured it out in 2009, and I’m late to the party.

Basically, if you are running Red Hat Enterprise Linux (or one of it’s clone siblings) on a Dell M600 blade, you’ll need to modify the default BIOS settings in a non-intuitive way or you’ll get an error on every boot-up.

IRQ handler type mismatch for IRQ 12

Call Trace:
[] setup_irq+0x1b7/0x1cf
[] serial8250_interrupt+0x0/0xfe
[] request_irq+0xb0/0xd6
[] serial8250_startup+0x43d/0x5dc
[] uart_startup+0x76/0x16c
[] uart_open+0x19e/0x427
[] tty_open+0x1e8/0x3b0
[] chrdev_open+0x14d/0x183
[] open_namei+0x2be/0x6ba
[] chrdev_open+0x0/0x183
[] __dentry_open+0xd9/0x1dc
[] do_filp_open+0x2a/0x38
[] do_sys_open+0x44/0xbe
[] tracesys+0xd5/0xdf

I knew this was a serial port issue from the second and fifth lines of the trace, but I couldn’t figure out why it was involving IRQ 12, which is normally used for SCSI cards or PS/2 mice.

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