New Lenovo ThinkPad notebooks are equipped with PrivacyGuard to limit the vertical and horizontal viewing angles of the LCD display. Previously, this was possible using special optical film coatings. The new function can be turned on / off depending on the situation.
PrivacyGuard is available on some newer ThinkPad models (T480s, T490 and T490s). The question of enabling support for this option in Linux was to define ACPI methods for enabling/disabling it in hardware.
On Linux 5.4+, PrivacyGuard is supported by the ThinkPad ACPI driver. In the /proc/acpi/ibm/lcdshadow file, you can see the state of the function and switch it by changing the value from 0 to 1 and vice versa.
Lenovo PrivacyGuard is only part of the x86 driver changes for Linux 5.4. There are also ASUS WMI driver updates, added accelerometer support for HP ZBook 17 G5 and ASUS Zenbook UX430UNR, Intel Speed Select driver updates, and more.
Source: linux.org.ru