In /dev/kmesg on my T14, I saw a message

	amlmapio: [0xffffff18-0x100000018] overlaps usable memory
	amlmapio: mapping \_SB.FRTP failed

Here is the relevant snippet from my DSDT:

    Scope (_SB)
    {
        ...

        OperationRegion (ECMC, SystemIO, 0x72, 0x02)
        Field (ECMC, AnyAcc, NoLock, Preserve)
        {
            ECMI,   8, 
            ECMD,   8
        }

        IndexField (ECMI, ECMD, ByteAcc, NoLock, Preserve)
        {
            Offset (0x08), 
            FRTB,   32
        }

        OperationRegion (FRTP, SystemMemory, FRTB, 0x0100)
        Field (FRTP, AnyAcc, NoLock, Preserve)
        {
		...
        }
    }

With some debugging output:

	amlmapio(\_SB.ECMC): Io       72 - 74
	rwreg(\_SB.ECMC): Io       [72+0]/1 <- 8
	rwreg(\_SB.ECMC): Io       [72+1]/1 -> 18
	amlmapio(\_SB.FRTP): Mem      ffffff18 - 100000018
	amlmapio: [0xffffff18-0x100000018) overlaps usable memory
	amlmapio: mapping \_SB.FRTP failed

It seems that libaml does not handle IndexField correctly and just did
a single read from ECMD after setting ECMI to 8, causing the FRTP
region to be evaluated as 0xffffff18-0x100000018. Instead, it should
be reading 4 bytes [18 c0 22 cc], evaluating it as
0xcc22c018-0xcc22118:

	amlmapio(\_SB.ECMC): Io       72 - 74
	rwreg(\_SB.ECMC): Io       [72+0]/1 <- 8
	rwreg(\_SB.ECMC): Io       [72+1]/1 -> 18
	rwreg(\_SB.ECMC): Io       [72+0]/1 <- 9
	rwreg(\_SB.ECMC): Io       [72+1]/1 -> c0
	rwreg(\_SB.ECMC): Io       [72+0]/1 <- a
	rwreg(\_SB.ECMC): Io       [72+1]/1 -> 22
	rwreg(\_SB.ECMC): Io       [72+0]/1 <- b
	rwreg(\_SB.ECMC): Io       [72+1]/1 -> cc
	amlmapio(\_SB.FRTP): Mem      cc22c018 - cc22c118

I wrote a patch (attached) to fix this, and it seems to work. Though,
it's not clear to me when things should be dereferenced. Previously,
the data field was dereferenced at evalfield, but the region and index
field were not until rwfield. After the patch, the index field is
also dereferenced in evalfield.

For BankField, the index *is* dereferenced in evalfield. I'm pretty
sure that this means that BankField does not work currently, since
store() just returns nil for 'f' objects. The bank selector will
never get set.

Anyway, I don't know if this solves any real problems; it's just
something I noticed and thought I'd try to fix.