Backlight message on boot

**Barhilton** · May 29th, 2013

I'm using a Dell XPS 15, 13.04. In order to get my backlight brightness control to work I have to use "acpi_backlight=vendor dell_laptop.backlight=0". But when I boot, I get the message: dell_laptop: '0' invalid parameter for 'backlight', at which my computer then continues to boot and works normally, with the brightness control working. It seems that I can change the '0' to anything, get the same message with the '0' changed to whatever I changed it to, and the brightness control still works. How can I get the message to go away?

**Toz** · May 29th, 2013

What happens if you remove "dell_laptop.backlight=0" from your boot parameters? Do the brightness controls still work? Perhaps the parameter is no longer required or valid.

**Barhilton** · May 29th, 2013

The brightness controls don't work properly without 'dell_laptop.backlight=0'. 'acpi_backlight=vendor' means that if I quickly and repeatedly press the key to change brightness, it eventually lowers, but sometime the down key makes it higher and visa versa, making it difficult to change. Adding 'dell_laptop.backlight=0' makes the controls work perfectly normally.

**Toz** · May 29th, 2013

Hmmm. Its odd then that it generates that message. The message seems to indicate that the parameter had no effect.

Could I have a look at your dmesg log file?

Code:

pastebinit /var/log/dmesg

...and post back the link that is generated.

And you can you also post back the results of:

Code:

cat /var/log/syslog | grep -i backlight

**Barhilton** · May 30th, 2013

http://paste.ubuntu.com/5716188/

Code:

May 29 17:36:09 benjamin-XPS-L501X kernel: [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=dell_laptopMay 29 17:36:09 benjamin-XPS-L501X kernel: [    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=dell_laptop
May 29 17:37:56 benjamin-XPS-L501X kernel: [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor backlight=dell_laptop
May 29 17:37:56 benjamin-XPS-L501X kernel: [    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor backlight=dell_laptop
May 29 17:39:30 benjamin-XPS-L501X kernel: [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=0
May 29 17:39:30 benjamin-XPS-L501X kernel: [    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=0
May 29 17:39:30 benjamin-XPS-L501X kernel: [   22.204699] dell_laptop: `0' invalid for parameter `backlight'
May 29 18:21:05 benjamin-XPS-L501X kernel: [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=0
May 29 18:21:05 benjamin-XPS-L501X kernel: [    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=0
May 29 18:21:05 benjamin-XPS-L501X kernel: [   22.595505] dell_laptop: `0' invalid for parameter `backlight'
May 30 10:26:06 benjamin-XPS-L501X kernel: [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=0
May 30 10:26:06 benjamin-XPS-L501X kernel: [    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=0
May 30 10:26:06 benjamin-XPS-L501X kernel: [   21.679170] dell_laptop: `0' invalid for parameter `backlight'
May 30 10:53:49 benjamin-XPS-L501X kernel: [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=hiimbarhilton
May 30 10:53:49 benjamin-XPS-L501X kernel: [    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=hiimbarhilton
May 30 10:53:49 benjamin-XPS-L501X kernel: [   21.666765] dell_laptop: `hiimbarhilton' invalid for parameter `backlight'
May 30 10:58:58 benjamin-XPS-L501X kernel: [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=0
May 30 10:58:58 benjamin-XPS-L501X kernel: [    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.8.0-22-generic root=UUID=df9e5312-fd68-4a0f-99fb-8b6667021bea ro quiet splash acpi_backlight=vendor dell_laptop.backlight=0
May 30 10:58:58 benjamin-XPS-L501X kernel: [   23.050627] dell_laptop: `0' invalid for parameter `backlight'

You're right, by the way, that in a sense the parameter has no effect. As you can see above, I tried changing the '0' to 'hiimbarhilton': the brightness controls still worked properly, and I still got the error message, just with 'hiimbarhilton' instead of '0'.

**Toz** · May 30th, 2013

Very interesting that the parameter makes the brightness work even though it seems to be invalid. Not sure what to say.

Guess you could ignore the message or file a bug report about it - your choice.

I also found this in your dmesg:

[ 24.211646] [Firmware Bug]: ACPI(PEGP) defines _DOD but not _DOS

A google search indicates that it is a common problem with this laptop, but I have not been able to come across any solutions. I believe this has to something to do with the video and may be the cause of the backlight issues. It maybe best to create a bug report and follow through with that avenue.