RE: [RFT] major libata update

Brown, Len
2006-05-18T00:36:35Z

>Many BIOS ACPI tables from years ago simply _assumed_ that you have
>hardcoded irq 14/15, even... Their irq descriptors for 14/15 would be
>absent or completely non-functional.
>
>Or maybe its the $pirq table I'm recalling. One of the two, anyway.

For x86, the ACPI interrupt configuration process is to identity-map
the IOAPIC entries below 16 1:1 PIC:IOAPIC,
unless there are interrupt source overrides
(such as commonly done to swizzle IRQ0 from a different pin)

This makes legacy-mode ATA happy. Hard code ATA to 14/15 and
off you go.

But there is a gray area where the ATA controller registers
as a PCI device, but Linux goes off and looks in the ACPI PRT
for that PCI-dev and finds no entry. So if you didn't
have the hard-coded 14/15, you'd be dead.

Then there are cases where the PRT specifies something
_other_ than 14/15 for ATA, and in that cases the hard-coded
default is the wrong thing to do; and the workaround is
to use BIOS SETUP options to be sure that ATA is set up
in legacy mode.

I suspect Linux could be smarter here. The 14/15 should be
the backup default for when the tables
don't give us anything else; not the only option.

-Len