# [solved] thinkpad E531 screen brightness

## defer-

I havent managed to get screen brightness to work on thinkpad E531. I tried ubuntu livecd and screen brightness controls work in it. I have built all the modules that was loaded on ubuntu livecd but brightness still doesnt work.

----------

## chithanh

Check if you have brightness controls in a subdirectory /sys/class/backlight/ and are using the thinkpad_acpi driver for the hotkeys.

Sometimes, acpi_backlight=vendor kernel parameter is necessary for backlight control to work.

----------

## defer-

I tried acpi_backlight=vendor but its still not working.

```

defer ~ $ ls /sys/class/backlight/intel_backlight/

actual_brightness  bl_power  brightness  device  max_brightness  power  subsystem  type  uevent

defer ~ $ dmesg | grep thinkpad

[    1.882819] Failed to find thinkpad-acpi symbol tpacpi_led_set

[   12.337470] thinkpad_acpi: ThinkPad ACPI Extras v0.25

[   12.337472] thinkpad_acpi: http://ibm-acpi.sf.net/

[   12.337473] thinkpad_acpi: ThinkPad BIOS HEET41WW (1.22 ), EC unknown

[   12.337474] thinkpad_acpi: Lenovo ThinkPad Edge E531, model 6885BPG

[   12.337846] thinkpad_acpi: Unsupported brightness interface, please contact ibm-acpi-devel@lists.sourceforge.net

[   12.339238] thinkpad_acpi: rfkill switch tpacpi_bluetooth_sw: radio is unblocked

[   12.339760] thinkpad_acpi: Console audio control enabled, mode: monitor (read only)

[   12.340826] input: ThinkPad Extra Buttons as /devices/platform/thinkpad_acpi/input/input9

```

----------

## chithanh

```
/sys/class/backlight/intel_backlight/
```

That intel_backlight control is usually a dummy which doesn't work. A working backlight control is provided by ACPI_VIDEO in most cases.

----------

## defer-

I can change brightness like this:

```
echo 2000 > /sys/class/backlight/intel_backlight/brightness
```

But brightness keys doesnt work?

----------

## sk8harddiefast

Did you check all the thinkpad options into kernel? Especially those for brightness, back light, FN keys etc. For ideapad laptops, they exist. Maybe for thinkpad too. Maybe they work the ideapad options on thinkpad too because both of them are lenovo.

----------

## defer-

```
<M>   Lenovo IdeaPad Laptop Extras 

<M>   ThinkPad ACPI Laptop Extras 

[*]     Console audio control ALSA interface

[ ]     Maintainer debug facilities

[ ]     Verbose debug mode

[ ]     Allow control of important LEDs (unsafe)

[*]     Video output control support

[*]     Support NVRAM polling for hot keys
```

----------

## chithanh

Can you check whether using the backlight keys actually changes the value of /sys/class/backlight/intel_backlight/brightness ?

The important option for backlight control is usually CONFIG_ACPI_VIDEO.

----------

## defer-

Backlight controls doesnt change /sys/class/backlight/intel_backlight/brightness.

I have CONFIG_ACPI_VIDEO=y.

I get this error to dmesg when pressing backlight controls:

[48742.386351] ACPI: Failed to switch the brightness

----------

## defer-

Putting 

```
acpi_osi='!Windows 2012'
```

 to kernel cmdline fixed the issue.   :Smile: 

----------

