# HP Envy 17 - Setting splash screen backlight for ATI

## lixo1

Dear all,

I'm having backlight problems with ATI Radeon HD 5850 on linux kernels > 2.6.32.

In fact the boot backlight is set to 0 when framebuffer is activated, if you have acpi enabled and a framebuffer device like ati or intel.

So now I'm running my configured kernel gentoo-r6 with only ati support, this is very good, the screen resolution is set automatically but I still having backlight problems.

As workaround, to set the backlight at login I'm using in /etc/rc.config, echo 10 > /sys/class/backlight/acpi_video0/brightness. 

Now I would like to have high backlight value for the boot splashscreen, how can I do that? Is there some file that can be read when the framebuffer is activated?

Thank you very much for any kind of help.Last edited by lixo1 on Mon Oct 04, 2010 1:05 pm; edited 1 time in total

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## Logicien

Hi,

I do not think you have a specific acpi video driver for Ati graphics cards in the ACPI kernel configuration menu. But check, a patch can exist. So you have to use or not the generic video acpi driver. If you use it, you probably have to compile it in the kernel or include it as module in an initrd. There is a module parameter, brightness_switch_enabled , that tell the driver it can change or not the brightness. So, if compile in the kernel, passing at boot time the parameter to the kernel 

```
video.brightness_switch_enabled=0
```

or if in module setting in /etc/modprobe.d/modprobe.conf

```
options video brightness_switch_enabled=0
```

and include modprobe.conf in the initrd, will disable the change of brightness when the video module load. The other option I see is not to compile at all the video driver or disable it. When you set the brightness manually, the ACPI support is suppose to not change it. Note that this is ony a try who have not been tested. You can see the meaning of the parameter here .

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## lixo1

Hi,

Thank you very much for your reply. I tried different configurations:

a) I just tried the brightness_switch_enable option on kernel with ATI Radeon driver activated, but unfortunately it doesn't work.

b) I disable all graphics drivers, the brightness still low at boot! (in this case I'm not using brightness_* option)

c) I disable acpi video from kernel, and I enabled ati driver, the backlight do not change (this is good!) but I lost backlight buttons control.

Well, now I have a big newbie question (I just finished the gentoo "console" installation): 

How is the difference between kernel ati driver and the ati proprietary driver available from their website?

If I'll use opengl applications what should I do?

Thank you again for your help!

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## Logicien

I only use the radeon and radeonhd drivers from Xorg. They give me enough accelaration for what I do. I can use direct rendering with them and composite. Compiz work normaly. I never install the proprietary Ati/Amd drivers. I think they give more performance. To confirm.

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## lixo1

Thanks for share your experience.

But in my case, the brightness_switch_enabled=0 doesn't work. I also tried to recompile my kernel changing the line in /usr/src/linux/drivers/acpi/video.c :

- static int brightness_switch_enabled=1

+static int brightness_switch_enabled=0

Nothing to do, what should I do? Report a bug report to the kernel? Where show that?

Thanks again.

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## lixo1

I found something really strange for Envy 14: http://www.andreas-demmer.de/en/2010/07/18/testbericht-linux-auf-dem-hp-envy-14/

It seems that the brightness is corrected by activating intel 910 driver and KMS?? I personally don't believe   :Shocked:  .

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## lixo1

I can confirm this issue is an acpi kernel bug or a bios bug, or both.

There is a patch from here:

https://bugzilla.kernel.org/show_bug.cgi?id=21212

Cheers.

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