4. Mainline device tree forked from the XPS 13 9345; stock tree as hardware map only

Status

Accepted 2026-10-21.

No mica DTS exists anywhere: not in mainline, not in the ChromiumOS 6.12 kernels, not on lore.
The stock DT is a Qualcomm vendor tree: an LZ4 base plus overlays in dtbo_a, with sde, qupv3_seN and qcom,… properties. Mainline cannot boot it.
The 9345 is a close match: address-by-address comparison (9345-dts-diff.md) shows mica reuses its retimer block, touchscreen, PCIe, eDP and uart21 debug console. The parts that differ are ChromeOS ones: cros-ec, Ti50, QSPI flash, a USB fingerprint MCU.

dts/x1e80100-google-mica.dts starts as an unmodified copy of mainline x1e80100-dell-xps13-9345.dts at a pinned commit (torvalds a804c57), committed alone. Mica’s changes go in later commits, so the diff is the record.
compatible = "google,mica", "qcom,x1e80100".
The stock tree is used only as a hardware map: buses, addresses, GPIOs, regulators, keymap. Every board-specific pin must trace to it. Anything copied from the 9345 without a stock match is marked “unverified”.
Checks before a commit counts: scripts/build-dtb.sh with no warnings, and dt-validate with no findings beyond the pending google,mica binding.

Upstreaming later needs a qcom.yaml binding patch, alphabetical node order and correct attribution.
Mainline changes to the 9345 file should be followed by re-basing onto a newer pinned commit.
Missing pieces (keyboard backlight, Glowbar, ALS, fans, audio, camera) get added once something boots.

EL2 changes come from mainline’s x1-el2.dtso, applied at build time (x1e80100-google-mica-el2.dtb), the way mainline builds every x1 board. The DTS stays the plain board file (What goes into the first-boot DTB).
One board fact traces to firmware source rather than the stock tree. The framebuffer reservation’s address matches the stock splash_region (0xe4800000). Its size, 0x2200000, comes from coreboot’s memlayout.ld; stock uses 0x21c0000 with no no-map.
/chosen/stdout-path = "serial0:115200n8" is now in the DTS, traced to the stock base (commit 709212e).