# How to use /sys/class/backlight?

## LonelyStar

Hi,

I have

```
CONFIG_BACKLIGHT_LCD_SUPPORT=y

CONFIG_BACKLIGHT_CLASS_DEVICE=y
```

in my .config (of my kernel).

/sys/class/backlight exists, but it is an empty directory ...

How do I use it or what do I have to do?

Thanks!

Nathan

----------

## timeBandit

 *Kernel configuration help for CONFIG_BACKLIGHT_CLASS_DEVICE wrote:*   

> This framework adds support for low-level control of the LCD backlight. This includes support for brightness and power.
> 
> To have support for your specific LCD panel you will have to select the proper drivers which depend on this option.

 Did you?

----------

## LonelyStar

Hi,

No I did not   :Embarassed: 

There are only to drivers to choose from:

- Generic (aka Sharp Corgi) Backlight Driver

- Frontpath ProGear Backlight Driver

I included both as modules and loaded the modules ... nothing in /sys/class/backlight.

I have a thinkpad. Until 2.6.24 the thinkpad_acpi kernel module provided an backlight interface, but now I get a message in dmesg:

thinkpad_acpi: standard ACPI backlight interface available, not loading native one.

Where could I find the native one?

Thanks!

Nathan

----------

## m_gustafsson

Hi,

did you solve this one?

I also see problems on my Thinkpad X60s with loading the Thinkpad-acpi:

```
dmesg | grep acpi

ACPI: LAPIC (acpi_id[0x00] lapic_id[0x00] enabled)

ACPI: LAPIC (acpi_id[0x01] lapic_id[0x01] enabled)

ACPI: LAPIC_NMI (acpi_id[0x00] high edge lint[0x1])

ACPI: LAPIC_NMI (acpi_id[0x01] high edge lint[0x1])

pnpacpi: exceeded the max number of mem resources: 12

thinkpad_acpi: ThinkPad ACPI Extras v0.17

thinkpad_acpi: http://ibm-acpi.sf.net/

thinkpad_acpi: ThinkPad BIOS 7BETC7WW (2.08 ), EC 7BHT37WW-1.10

thinkpad_acpi: Lenovo ThinkPad X60s

thinkpad_acpi: radio switch found; radios are disabled

thinkpad_acpi: standard ACPI backlight interface available, not loading native one...
```

I also cannot load the acpi module from a terminal:

```
# modprobe thinkpad_acpi   

FATAL: Module thinkpad_acpi not found.
```

On the other hand I have this in my directories:

```
# ls /sys/class/backlight/           

acpi_video0  acpi_video1
```

The kernel options which I have guessed matters are:

```
# cat /usr/src/linux/.config | grep BACKLIGHT

CONFIG_BACKLIGHT_LCD_SUPPORT=y

CONFIG_BACKLIGHT_CLASS_DEVICE=y

CONFIG_BACKLIGHT_CORGI=y

CONFIG_BACKLIGHT_PROGEAR=y
```

And:

```
# cat /usr/src/linux/.config | grep THINKPAD 

CONFIG_THINKPAD_ACPI=y

CONFIG_THINKPAD_ACPI_DEBUG=y

CONFIG_THINKPAD_ACPI_BAY=y
```

Best regards, Mats

----------

