powerd uses the udev interface to learn about hardware changes.
The InputDeviceController class is responsible for setting input devices' inhibit udev system attributes (to suppress events) and wakeup sysfs attributes (to enable or disable their ability to wake the system) appropriately depending on the system's current mode. For example, the touchscreen should be ignored while the system is in docked mode with its lid closed.
This behavior is configured via udev tags that are set on devices by the 90-power-id.rules and 92-powerd-tags.rules files:
| Tag | Description |
|---|---|
inhibit | If set, powerd will inhibit the device when not usable |
usable_when_docked | Device is usable when system is docked |
usable_when_display_off | Device is usable when in clamshell mode with display off |
usable_when_laptop | Device is usable when in clamshell mode |
usable_when_tablet | Device is usable when in tablet mode |
wakeup | If set, powerd will manage the device's wakeup attribute |
wakeup_when_docked | Enable wakeup when system is docked |
wakeup_when_display_off | Enable wakeup when in clamshell mode with display off |
wakeup_when_laptop | Enable wakeup when in clamshell mode |
wakeup_when_tablet | Enable wakeup when in tablet mode |
wakeup_only_when_usable | Shorthand for enabling wakeup only when usable |
wakeup_disabled | Unconditionally disable wakeup (if wakeup is also set) |
If only the wakeup tag is set, wakeup will be unconditionally enabled. If one or more wakeup_when_* tags are also present, wakeup will be enabled only while in the requested modes.
Boards can create and install their own udev rules with prefix 91- to override generic internal/external_[type] roles, or create udev rules with prefix 93- to override the specific tags above.
