gs201 felix: display (DPU/DECON/DSIM) bring-up

[ccrutchf]

Goal

Get the panel(s) lit on Pixel Fold (felix), so kernel printk and console are visible without requiring UART. Chosen as the next major bring-up effort over CS40L26 haptic and USB-gadget CDC.

Why display over haptic / USB-gadget

• Display is on a fully independent hardware path from USB-C (DPU → DSIM → DSI → panels, dedicated cmu_dpu clocks, dedicated pinctrl banks). UART stays continuously available throughout the entire bring-up — every probe failure, every crash, we see live.
• USB-gadget would have a chicken-and-egg problem: the bring-up itself has the cable conflict (UART + USB share the USB-C port), and the thing we'd be building is the only channel that would replace UART.
• Bigger payoff than haptic. Once display works, kernel boot is visible directly, login prompt is on the panel, and a basic graphical desktop is plausible later. Comparable effort to haptic but with much higher value per unit of work.

Hardware

felix is a foldable with two command-mode panels:

• samsung-ana6707-f10 — inner foldable, 1840×2208, product id 0x8408
• ea8182-f10 — cover, 1080×2092, product id 0xd18018

Command-mode panels need DECON to drive frame triggers; simple-framebuffer will not work (already proven on AOSP).

Mainline gap

• samsung-dsim bridge: present in mainline, may need a gs201 compat
• DECON for gs101/gs201: not in mainline. Closest: exynos7-decon, exynos5433-decon
• AOSP reference: private/google-modules/display/ (DPU CAL cal_9855 for gs201, panel drivers under panels/, samsung/cal_common helpers)

Milestone plan

Each step testable with UART:

1. DT skeleton. Add cmu_dpu clocks (or stub like cmu_peric0), DECON/DSIM/panel nodes. Win: kernel boots without crashing on new DT.
2. DECON probe stub. Driver probes, can read a known register, doesn't drive hw.
3. DSIM probe via mainline samsung-dsim. Add gs201 compat if needed. Win: read panel product ID via DSI MIPI (expect 0x8408).
4. Panel driver port for samsung-ana6707-f10 from private/google-modules/display/panels/ — long init command sequence.
5. DECON scan-out one window to DSIM with a framebuffer.
6. fbcon enabled → kernel printk visible on panel.

Tracker

This is an epic. Sub-issues per milestone will be filed as work begins.