HOWTO: Make brightness control Fn keys work correctly on HP DV2000 with Ubuntu 7.04(Feisty)

Problem:
I’ve a hp dv2210us (one of the dv2000z series) laptop with feisty installed. Almost everything works fine, except that it is not easy to adjust the brightness easily. Fn keys don’t work, no slider in Gnome Power Manager. The only way to adjust the brightness is "sudo echo" a correct value to /proc/acpi/video/VGA/LCD/brightness, which is quite inconvenient. More precisely, the Fn keys may sometimes turn the screen to either brightest or dimmest. A careful study shows that the problem resides in the kernel module "video". Whenever the keys are pressed, the module will try to adjust the brightness as well as trigger a signal might be caught by acpi daemon. However, for some reason that I don’t know, the module cannot adjust the brightness correctly on my laptop.

Solution:
The idea is to adjust the brightness through acpi daemon rather than the kernel module. So what we are going to do is to modify the kernel module a bit and add some small scripts to the acpi daemon. Here we go. I hope this howto may help those who have the similar problems.

************Please remember to do the backup before any modification and file replacements.********

1. Install the source package
sudo apt-get install linux-source-2.6.20
cd /usr/src
sudo tar xvjf linux-source-2.6.20.tar.bz2

2. Modify the kernel module.
cd /usr/src/linux-source-2.6.20/drivers/acpi
sudo gedit video.c
**find the code block below:
…
case ACPI_VIDEO_NOTIFY_INC_BRIGHTNESS: /* Increase brightness */
case ACPI_VIDEO_NOTIFY_DEC_BRIGHTNESS: /* Decrease brightness */
case ACPI_VIDEO_NOTIFY_ZERO_BRIGHTNESS: /* zero brightnesss */
case ACPI_VIDEO_NOTIFY_DISPLAY_OFF: /* display device off */
acpi_video_switch_brightness(video_device, event);
acpi_bus_generate_event(device, event, 0);
break;
default:
…
**edit this part according to below:
…
case ACPI_VIDEO_NOTIFY_ZERO_BRIGHTNESS: /* zero brightnesss */
case ACPI_VIDEO_NOTIFY_DISPLAY_OFF: /* display device off */
acpi_video_switch_brightness(video_device, event);
acpi_bus_generate_event(device, event, 0);
break;
case ACPI_VIDEO_NOTIFY_INC_BRIGHTNESS: /* Increase brightness */
case ACPI_VIDEO_NOTIFY_DEC_BRIGHTNESS: /* Decrease brightness */
acpi_bus_generate_event(device, event, 0);
break;
default:
…
Save and quit.

3. Recompile and replace the kernel module
cd /usr/src/linux-source-2.6.20/drivers/acpi
sudo gedit makevideo
write the following code into the newly created file.

KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)

default:
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

Save and quit.
sudo make -f makevideo
sudo cp video.ko /lib/modules/`uname -r`/kernel/drivers/acpi/

4. Add acpi events
cd /etc/acpi/events
sudo gedit hp-brightness-up
write the following contents into the newly created file:

event=video LCD 00000086 00000000
action=/etc/acpi/hpbrightnessup.sh

Save and quit.
sudo gedit hp-brightness-down (same as before)

event=video LCD 00000087 00000000
action=/etc/acpi/hpbrightnessdown.sh

Save and quit.

5. Add new acpi scripts to adjust the brightness
cd /etc/acpi
cat /proc/acpi/video/VGA/LCD/brightness
please pay attention to the output of levels.
mine is : "levels: 100 60 20 28 36 44 52 60 68 76 84 92 100"
if yours is different you may have to change the numbers in the following scripts.
sudo gedit hpbrightnessup.sh

#!/bin/sh

value="`cat /proc/acpi/video/VGA/LCD/brightness | grep current: | awk ‘{print $2;}’`"
if [ $value -eq 0 ]
then
value=92
fi
if [ $value -ge 92 ]
then
value=92
else
value=`expr $value + 8`
fi
echo $value > /proc/acpi/video/VGA/LCD/brightness

Save and quit.
sudo gedit hpbrightnessdown.sh

#!/bin/sh
value="`cat /proc/acpi/video/VGA/LCD/brightness | grep current: | awk ‘{print $2;}’`"
echo $value
if [ $value -eq 0 ]
then
value=92
fi
if [ $value -le 20 ]
then
value=20
else
value=`expr $value – 8`
fi
echo $value > /proc/acpi/video/VGA/LCD/brightness

Save and quit.
sudo chmod +x hpbrightness*.sh

6. Done
You may find the Fn keys work correctly after rebooting the computer.
I wish I made everything clear here, however, if any questions, plz let me know.

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