Screen Brightness on a KiraBook with Ubuntu 14.04

The backlight on my new laptop was not working - a Toshiba KiraBook running Ubuntu 14.04. The buttons for screen brightness (F2 and F3) did not cause the brightness to change. Also, the OSD feedback incorrectly showed “Power Manager” for brightness-down and no OSD feedback for brightness-up.

I have changed the BIOS to recognise the keys as F1-12 keys, requiring the Fn key to activate the hotkey functionality (default is to have them as hotkeys and Fn makes them F1-12).

Setting brightness manually #

Following the steps at https://wiki.ubuntu.com/Kernel/Debugging/Backlight I found that I could manually adjust the brightness from a terminal with

sudo su
cd /sys/class/backlight/intel_backlight
cat brightness
echo 400 > brightness

The value of cat brightness at boot (which seems to be full brightness) is 765, so 400 should be about half way, and certainly appears to my eyeballs to be about that.

On a side-note, I did not have to add a kernel boot parameter to grub, the manual change worked without it (ie I did not need to add acpi_backlight=vendor to grub)

Fixing hotkeys #

Following https://wiki.ubuntu.com/Hotkeys/Troubleshooting

xev #

xev did not return any output for the brightness hotkeys, nor for the volume keys (which are working). Looks like xev isn’t going to show me any useful hotkey data.

evtest #

I tried to detect it with sudo evtest and got nothing came up, whereas I did get feedback for volume controls, so it looks like it must be getting detected as an acpi event instead of a keyboard event. Here’s the output:

/dev/input/event0:  Power Button
/dev/input/event1:  Lid Switch
/dev/input/event2:  Power Button
/dev/input/event3:  AT Translated Set 2 keyboard
/dev/input/event4:  Toshiba input device
/dev/input/event5:  SynPS/2 Synaptics TouchPad
/dev/input/event6:  Video Bus
/dev/input/event7:  HDA Intel PCH Headphone
/dev/input/event8:  HDA Intel PCH Mic
/dev/input/event9:  HDA Intel HDMI HDMI/DP,pcm=8
/dev/input/event10: HDA Intel HDMI HDMI/DP,pcm=7
/dev/input/event11: HDA Intel HDMI HDMI/DP,pcm=3
/dev/input/event12: TOSHIBA Web Camera - HD
/dev/input/event13: Microsoft Microsoft 3-Button Mouse with IntelliEye(TM)
/dev/input/event14: ELAN Touchscreen

I pressed 3 (enter)

Input driver version is 1.0.1
Input device ID: bus 0x11 vendor 0x1 product 0x1 version 0xab41
Input device name: "AT Translated Set 2 keyboard"
Supported events:
----
[Long list of supported keycodes, there were none related to brightness - some 'interesting' ones are shown below]
    Event code 114 (KEY_VOLUMEDOWN)
    Event code 115 (KEY_VOLUMEUP)
----
Testing ... (interrupt to exit)
Event: time 1397023765.706042, type 4 (EV_MSC), code 4 (MSC_SCAN), value 1c
Event: time 1397023765.706042, type 1 (EV_KEY), code 28 (KEY_ENTER), value 0
Event: time 1397023765.706042, -------------- SYN_REPORT ------------

No further output when using brightness up/down hotkeys

acpi_listen #

Running acpi_listen I saw that brightness hotkeys were being detected incorrectly as an acpi event.

Brightness down (Fn-F2):

button/battery BAT 00000080 00000000 K

Brightness up (Fn-F3):

button/sleep SBTN 00000080 00000000 K

Related info #

http://ubuntuforums.org/showthread.php?t=2208665

Addendum #

As of Ubuntu 16.04 this issue has been fixed and the backlight keys function correctly on the KiraBook.