Suspend on Dell XPS 9550

[coypu%sdf.org@localhost]

Hi folks, I have this machine (Dell XPS 15" 9550) I'd like to get
suspend on: http://dmesgd.nycbug.org/index.cgi?do=view&id=3729

Currently, instead of resume, I get the same mode this person is
describing while resuming from *Windows*:
https://www.youtube.com/watch?v=x3QV38YFb9g
(IIRC, suspend does work on Linux)

Instead of proper resume, it gets in some intermediate state where
the keyboard backlight works, but not much else.

Possibly problematic hardware:
- tpm at isa, I hear tpm(4) needs to save state for resume to work.
- dual gpu nvidia GTX 960M / skylake graphics. we only use skylake, but
  sometimes (e.g. EFI boot), the nvidia card is attempted.
- thunderbolt?

Attempted:
- Updated BIOS to the latest version (1.8, released a few days ago)
- Attempted various configurations of disabling most drivers possible to
  disable, under the assumption that one of them is causing suspend
  issues.
- Done the above after disabling as many things in BIOS as possible.

I frequently get ACPI errors, including at suspend. I know ACPI has a
debug mode, but the shutdown wipes our my dmesg buffer, and I don't have
console.

Any suggestions for things to try?