# [SOLVED] No brightness control with gentoo-sources 3.2.1

## solpeth

After upgrading my kernel to gentoo-sources 3.2.1, I noticed that I had no brightness control. In my gentoo-sources 3.1.10 kernel, brightness worked; I use xfce4-power-manager to use my hardware keys to control the brightness.

I've looked around on google, but I've found nothing related to my issue. I've come across suggestions to set acpi_osi=Linux but I don't know where exactly to set it in the grub.conf...  :Rolling Eyes: 

I noticed that I have no /sys/class/backlight/acpi_video0/brightness file when I boot in with the 3.2.1 kernel, but with 3.1.10 it's there... I don't understand much at all about how that is supposed to work, but that's what I see. I thought this might be related to the problem.

If it helps, in a previous Gentoo installation I had the same problem when updating from 3.0.6 to 3.1.6. I don't think it's the actual 3.2.1 kernel version for that reason - I might have overlooked some sort of configuration, or some other issue - but I don't understand it enough to comment.

If you need any other information, please let me know.

ThanksLast edited by solpeth on Sun Mar 25, 2012 2:41 am; edited 1 time in total

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## sebaro

Do you have backlight support set in kernel?

> grep BACKLIGHT /boot/config

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## solpeth

I ran grep BACKLIGHT /boot/config, but /boot/config doesn't exist:

grep: /boot/config: No such file or directory

So I ran grep in /usr/src/linux/.config and this was the output:

```
gentoo ~ # grep BACKLIGHT /usr/src/linux/.config

# CONFIG_FB_BACKLIGHT is not set

CONFIG_BACKLIGHT_LCD_SUPPORT=y

CONFIG_BACKLIGHT_CLASS_DEVICE=y

CONFIG_BACKLIGHT_GENERIC=y

# CONFIG_BACKLIGHT_PROGEAR is not set

# CONFIG_BACKLIGHT_APPLE is not set

# CONFIG_BACKLIGHT_SAHARA is not set

# CONFIG_BACKLIGHT_ADP8860 is not set

# CONFIG_BACKLIGHT_ADP8870 is not set

# CONFIG_LEDS_TRIGGER_BACKLIGHT is not set

```

I'm starting to think it's my BIOS not playing nice with the 3.2.1 kernel... could this be the problem?

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## sebaro

Make sure lowlevel LCD and backlight controls are built-in:

> grep Lowlevel /usr/src/linux/.config

You can also pass "acpi_osi=Linux acpi_backlight=vendor" options to the kernel in the grub config file. Then the brightness file will be /sys/class/backlight/vendor_backlight/acpi_video0/brightness.

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## solpeth

```
gentoo ~ # grep Lowlevel /usr/src/linux/.config
```

returned no results. I tried adding "acpi_osi=Linux acpi_backlight=vendor" to the grub.conf but it made no difference, the /sys/class/backlight/*/brightness file still doesn't exist. In fact, nothing in the /sys/class/backlight/ directory exists when I use the 3.2.1 kernel, but in the 3.1.10 kernel it's all there.

Just so I'm sure, I add those boot options as follows, right?

```
title Gentoo Linux 3.2.1

root (hd0,0)

kernel /boot/linux-3.2.1-gentoo-r2 root=/dev/sda3 acpi_osi=Linux acpi_backlight=vendor

```

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## psheldon

[quote]I might have overlooked some sort of configuration, or some other issue - but I don't understand it enough to comment. [/quote]

Me too!  :Smile:   My problem is random crashes and reboots with KDE, 3.1.10 is fine! I am using it now, I keep the previous kernel in case. 3.2.1 is NOT nice.

I do have an i7.

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## sebaro

Try to build these options in kernel:

[*] Backlight & LCD device support ---> 

--- <*> Lowlevel LCD controls

--- <*> Lowlevel Backlight controls

------ <*> Generic (aka Sharp Corgi) Backlight Driver

First try with "Lowlevel Backlight controls" only.

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## psheldon

Sebaro, Thanks that worked for me!

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## solpeth

I actually ended up doing a clean install of gentoo, and surprisingly the 3.2.1-r2 gentoo-sources kernel works. As far as I know it's configured exactly how I had it on my previous installation too, but I'll wait again and see what happens on the next stable kernel. If it happens again there is a definite trend here; three of the same occurrences in a row is unlikely to be by coincidence. I have a feeling it has something to do with my BIOS, at least being out of date or something similar (unfortunately I couldn't update it even if I wanted to, because I don't have Windows on my system). Other than that I'm stabbing in the dark; I have no idea where to begin for this issue. I have an HP 6930p and I can't even run FreeBSD smoothly because of constant acpi errors, so it's something.

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## solpeth

One of the Gentoo devs, 'chithead', ended up helping me out on the #gentoo IRC channel (the Gentoo community is just awesome  :Wink:  )

If anyone runs into the same problems, I just had to go about enabling ACPI_VIDEO and HP_WMI (my laptop is an HP), which ended up fixing the issue.

SOLVED.

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