The PCI Specification states that devices that implement
a bridge and a secondary bus must swizzle (rotate) the
interrupt pins according to the table below:
Child Dev # Child PIN Parent PIN
0,4,8,12... A/B/C/D A/B/C/D
1,5,9,13... A/B/C/D B/C/D/A
2,6,10,14.. A/B/C/D C/D/A/B
3,7,11,15.. A/B/C/D D/A/B/C
Which is also described by this equation:
PIN_parent = (Pin_child + Dev_child) % 4
When a device is found and its bus number is greater than 0,
it is on a bridge and needs to be swizzled. Following the
string of parents up to the root bus and swizzling as we go
gives us the desired swizzling result. When BIOS_SPEW is
defined, it will print out each step of the swizzling process.
Change-Id: Icafeadd01983282c86e25f560c831c9482c74e68
Signed-off-by: Martin Roth <gaumless@gmail.com>
Reviewed-on: http://review.coreboot.org/5734
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-by: Mike Loptien <mike.loptien@se-eng.com>
0f5cf5e45b