@downey The only real challenge was with #EFI, and I may have brought that on myself by trying to do the whole thing with Secure Boot enabled for Grub and Debian. I eventually got rEFInd working and went "it's working, so I'm not touching Secure Boot again!"
Really didn't have any other issues. I used the Debian "firmware inclusive" installer and then added the linux-surface kernel post-install but that was all pretty easy.
@jgoerzen Nice. It looks like the new-ish https://github.com/linux-surface/surface-uefi-firmware will take care of at least some of the problems I had. Guess I have a summer project now.
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