Linux 5.4 Bringing Support For Lenovo's "PrivacyGuard" On Newer ThinkPads
Lenovo PrivacyGuard allows restricting the usable vertical/horizontal angles of the laptop's LCD panel so that ideally no one else but the user can view the screen contents. Unlike film covers or other practices, PrivacyGuard can be easily enabled/disabled depending upon your location. PrivacyGuard hasn't worked under Linux up to this point but is coming now with Linux 5.4.
PrivacyGuard doesn't work with any ThinkPad but currently is found in their higher-end models like the T480s, T490, and T490s models. Enabling the support under Linux was a matter of figuring out the ACPI methods for enabling/disabling the hardware feature for the display.
With Linux 5.4+, PrivacyGuard is supported as part of the existing ThinkPad ACPI driver and will expose /proc/acpi/ibm/lcdshadow for viewing the state of the feature and toggling its functionality. Writing 0 or 1 to that procfs node will toggle the feature.
This Lenovo PrivacyGuard is part of the x86 platform driver changes for Linux 5.4. This early Linux 5.4 pull request also has ASUS WMI driver updates, accelerometer support for the HP ZBook 17 G5 and ASUS Zenbook UX430UNR, Intel Speed Select driver updates, and various other updates.