6. Debug console through GSC CCD and a SuzyQ, read-only while CCD is locked

Status

Accepted 2026-10-21.

First boot needs a console that works before display or USB drivers do. Tested 2026-10-21 (ccd-gsc.md):

A Fyra Labs SuzyQ in the Googlebook’s left USB-C port exposes the Ti50 as 18d1:5066, with Shell, AP, EC and FPMCU consoles.
ccdstate shows UARTAP+TX: the AP UART is bridged both ways while CCD is Locked.
The stock and mainline DTs both name uart21 (0x894000) as serial0.
Opening CCD (gsctool -a -o plus power-button presses) needs developer mode, and it changes GSC state.

Kernel console: uart21 is the first-boot console: stdout-path = "serial0:115200n8", console=ttyMSM0,115200. the build host reads it through the SuzyQ’s AP console.
Read only: agents run the SuzyQ consoles read-only. Before reading, run stty raw -echo on the tty so nothing echoes back. On the GSC shell, agents send only read-only commands (version, ccdstate, help). Never ccd open/unlock/reset, wp, reboot or any flash command.
Opening CCD (for a full AP flash backup over raiden_debug_spi) is an owner decision. It happens after unlocking and gets its own ADR.
the build host access: the uaccess udev rule /etc/udev/rules.d/70-ti50-ccd.rules (owner choice over joining uucp).

The left USB-C port is taken by the SuzyQ during bring-up. Boot media and power go through the right port (a hub with PD pass-through) or the spare SSD.
If the AP console stays silent under Linux, the fallbacks are ramoops (depthcharge always reserves it) and the panel.

The DTS has the console now: it sets stdout-path = "serial0:115200n8" (commit 709212e).
Read-only still applies with our own kernel: the first-boot initramfs prints its captures, then reboots, and has no shell (Initramfs contents and pass criteria).
Logs: raw AP-console logs go to dumps/firstboot/.
Second channel: when the console is silent, the stock OS’s dropbox SYSTEM_LAST_KMSG holds the failed boot’s last 64 KiB (stock pstore).