Investigation on a returned unit (docs/display-blank-investigation.md):
the dark-panel/backlight-on failure reproduces with a warm reboot or a
200 ms pulse on the panel reset line, with no kernel message. After the
U-Boot logo hand-off the panel powers/avee GPIOs stay undriven inputs.
- Fresh boot: DPMS off/on before the UI starts (unit Before=buttontask),
so the driver runs the full panel power-on and drives those lines.
- Daily preventive re-init (01:30 UTC, or every 24 h of uptime without
NTP); not counted towards reboot escalation.
- Previous boot found by saved boot_id, not 'journalctl -b -1' (clock
jumps reorder boots); log cold/warm boot from the rk809 RTC (reset to
2017-08-04 on power loss); keep the RTC set from NTP; uptime in every
incident line; loop timers on the monotonic clock.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
GrigoandClaude Opus 5.5
66578a0925