Issue #647 has been reported by Christian Schrötter. ---------------------------------------- Bug #647: ec/lenovo/h8: ThinkLight is always-on with specific `backlight` CMOS options on ThinkPad X230 https://ticket.coreboot.org/issues/647
* Author: Christian Schrötter * Status: New * Priority: Low * Target version: none * Start date: 2026-05-25 * Affected versions: main * Affected hardware: Lenovo ThinkPad X230 ---------------------------------------- The ThinkPad X230 supports the following values for the option *"Keyboard Illumination Device"* (Config » Keyboard/Mouse) in the stock BIOS. These states are represented in EC RAM register `0x01` via bits 2-3: * **Both**: `0x00` * **Keyboard Backlight Only**: `0x04` (bit 2 set) * **ThinkLight Only** : `0x08` (bit 3 set) coreboot implements this setting via the `backlight` CMOS option. Additionally, there's a 4th (undocumented?) value in coreboot, which is apparently supported by some ThinkPads: * **None** : `0x0c` (bit 2 and 3 set) I've successfully tested `backlight=Keyboard` and `backlight=None` on a T440p with coreboot, without any issues. ## Bug description However, X230's behaviour under coreboot is broken for specific settings: * `backlight=Both` and `backlight=Thinklight only`: Works as expected. * `backlight=None` or `backlight=Keyboard only`: ThinkLight is always-on! In this "always-on" state, there's no way to turn off ThinkLight. Even pressing Fn+Space is completely ignored by the EC. ## Debugging Attempts & Observations * I suspected a race condition during EC initialization and tried to forcefully disable the ThinkLight during `h8_enable()` before `config1` gets written. - Result: This didn't work. The ThinkLight remains always-on. ([see my attempt on GitHub](https://github.com/froonix/coreboot/commit/c87e9469eb7deb885e4affce10d2ec27745b2001)) * It appears that setting bit 2 in `0x01` doesn't just disable the feature, but rather locks out the EC entirely from controlling the physical GPIO pin, leaving it floating/high. * The catch (timing): There is one exception! The ThinkLight correctly switches off during the very first cold boot right after flashing the BIOS region; when the MRC cache is invalid. The lengthy RAM training delay somehow prevents the issue. This strongly points towards a timing or race condition issue during the EC's own initialization phase versus coreboot sending the commands. Currently, I'm out of ideas on how to properly debug or fix this EC quirk. Any hints from a coreboot veteran would be highly appreciated. :-) -- You have received this notification because you have either subscribed to it, or are involved in it. To change your notification preferences, please click here: https://ticket.coreboot.org/my/account _______________________________________________ coreboot mailing list -- [email protected] To unsubscribe send an email to [email protected]
