BufferField implicit conversion not supported in OperationRegion command

[martin-hughes]

NB: This issue repros only if #272 is worked around, otherwise that hits first.

My machine has an ASL block that simplifies down the snippet at below. The crate can't parse the OperationRegion command - ObjectNotOfExpectedType { expected: Integer, got: BufferField }.

I think BufferField should be implicitly converted to Integer here (and possibly other places too)?

Failing snippet

DefinitionBlock ("", "SSDT", 2, "AMD", "AmdTable", 0x00000002)
{
    Scope (\_SB)
    {
        Name (ADAT, Buffer (0x0010) //keep
        {
            /* 0000 */  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // ........
            /* 0008 */  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // ........

        })

        Device (AWR0)
        {
            Name (_HID, EisaId ("PNP0C02") /* PNP Motherboard Resources */)  // _HID: Hardware ID
            Name (_UID, 0x90)  // _UID: Unique ID
            Device (ABR0)
            {
                Name (_HID, EisaId ("PNP0C02") /* PNP Motherboard Resources */)  // _HID: Hardware ID
                Name (_UID, 0x80)  // _UID: Unique ID
                OperationRegion (A053, SystemMemory, (DerefOf (\_SB.ADAT [(0x04)])), 0x1000) // <--- this line fails
                Field (A053, ByteAcc, NoLock, Preserve)
                {
                    Offset (0x18),
                    A, 8
                }
            }
        }
    }
}

Quite happy to take a look if you give me a summary of how this is intended to work.

[IsaacWoods]

Yes, this is a failure of our reference handling (reference semantics in AML are fairly tricky and expected behaviour (as in, what the NT interpreter does) is well known to be different to the spec and from ACPICA's interpreter in many cases; but ours is definitely suboptimal.

I think the way we need to handle these cases is by having a new ReferenceKind for Index references. This will be produced by DefIndex (the \_SB.ADAT [(0x04)] above) and then the indexing operation actually happens on the DerefOf. Very happy to review a PR if you want to work on this or will have a look when I get the chance.