Accelerometer and screen orientation in GNOME3

Sat, 23 Feb 2013 09:53:55 GMT

Following up on using Debian on the WeTab with GNOME Shell I had a look at automatically adjusting the screen orientation when rotating the device.

The accelerometer is handled in the asus_laptop module since kernel 3.2, so this shows up in /proc/bus/input/devices:

I: Bus=0019 Vendor=0000 Product=0000 Version=0000
N: Name="Pegatron Lucid Tablet Accelerometer"
P: Phys=pega_accel/input0
S: Sysfs=/devices/platform/asus_laptop/input/input4
U: Uniq=
H: Handlers=event4 js0
B: PROP=0
B: EV=9
B: ABS=7

Whenever the screen orientation changes the driver emits a udev event. The helper in /lib/udev/accelerometer processes it thanks to /lib/udev/rules.d/61-accelerometer.rules, determines the orientation and adds the ID_INPUT_ACCELEROMETER_ORIENTATION property to the event which can be checked with udevadm monitor --property:

UDEV  [5778.534171] change   /devices/platform/asus_laptop/input/input4 (input)
ABS=7
ACTION=change
DEVPATH=/devices/platform/asus_laptop/input/input4
EV=9
ID_FOR_SEAT=input-platform-asus_laptop
ID_INPUT=1
ID_INPUT_ACCELEROMETER=1
ID_INPUT_ACCELEROMETER_ORIENTATION=right-up
ID_PATH=platform-asus_laptop
ID_PATH_TAG=platform-asus_laptop
MODALIAS=input:b0019v0000p0000e0000-e0,3,kra0,1,2,mlsfw
NAME="Pegatron Lucid Tablet Accelerometer"
PHYS="pega_accel/input0"
PRODUCT=19/0/0/0
PROP=0
SEQNUM=1550
SUBSYSTEM=input
TAGS=:seat:
UDEV_LOG=3
USEC_INITIALIZED=6154288

This is captured by gnome-settings-daemon (>=3.2) that adjusts the screen rotation using xrandr2 accordingly. This can be checked by running gnome-settings-daemon with --debug. The old way of using xinput events is no longer supported.

Unfortunately Debian's udev has a minor bug that misdetects the input device so this patch is needed to have the screen orientation changed automatically on the WeTab.

This blog is flattr enabled.