# Is it possible to control backlight with ATI KMS?

## VinzC

Hi.

It's been a while I'd like to use Xfce's backlight applet with my laptop (a Dell XPS Studio) even though the Fn+<backlight +/-> combo works, I'd just like to have that eye-candy  :Wink: . The applet always reports there's no device. I guess I need to enable some kernel features, right? So which are the options I need to enable? I have no /sys/devices/virtual/backlight entry.

```
---------------------------------------------------

       Xfce power manager version 1.0.10

With policykit support

With network manager support

With DPMS support

---------------------------------------------------

Can suspend: True

Can hibernate: True

Can spin down hard disks: True

Authorized to suspend: True

Authorized to hibernate: True

Authorized to shutdown: True

Authorized to spin down hard disks: True

Has brightness panel: False

Has power button: True

Has hibernate button: True

Has sleep button: True

Has LID: True
```

System:gentoo-sources-2.6.38ATI Radeon Mobility 3670xf86-video-ati-9999Thanks in advance.

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## chithanh

The correct sysfs path should be /sys/class/backlight

Ensure that you have 

```
CONFIG_BACKLIGHT_CLASS_DEVICE=y

CONFIG_ACPI_VIDEO=y
```

set in your kernel config.

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## VinzC

Thanks chithanh. Indeed I have both options set to Y and directory /sys/class/backlight is empty.

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## chithanh

That is strange. Did you enable the vendor specific notebook driver? DELL_LAPTOP for older, DELL_WMI for newer models.

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## Ant P.

I was wondering a similar thing - why can't I adjust my desktop LCD's backlight/other stuff over DDC? I *know* it's possible because it worked on an i945 in ms windows...

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## VinzC

 *chithanh wrote:*   

> That is strange. Did you enable the vendor specific notebook driver? DELL_LAPTOP for older, DELL_WMI for newer models.

 

No, I think I didn't. Will try that. When should I consider it's a «old» laptop? The XPS Studio is not from last year but maybe two or three at most.

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## chithanh

If you are unsure, enable both and check dmesg which one becomes active.

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## VinzC

 *chithanh wrote:*   

> If you are unsure, enable both and check dmesg which one becomes active.

 

Will do that and report here. Thanks a lot for your hints.

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