There's a HP laptop out there where the MXM version in the VBIOS doesn't
match what the ACPI implementation is expecting.  These tables will accept
0x00 to MXMS to return latest version, but *only* if MXMI has been called
first..
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

There's at least one known case where our shadowing code is buggy, and we
fail init.  Until we can be confident we're doing all this correctly, lets
succeed and risk crazy bios tables rather than failing for perfectly valid
configs too.
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

Untested, -ENOHW.
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

The DCB table provided by the VBIOS on most MXM chips has a number of
entries which either need to be disabled, or modified according to the
MXM-SIS Output Device Descriptors.

The x86 vbios code usually takes care of this for us, however, with the
large number of laptops now with switchable graphics or optimus, a lot
of the time nouveau is responsible for POSTing the card instead - leaving
some fun situations like, plugging in a monitor and having nouveau decide
3 connectors actually just got plugged in..

No MXM-SIS fetching methods implemented yet.
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>