acpi video driver and 2.6.30

[Thierry Chatelet <tchatelet@free.fr>]

Following my previous post (2.6.30 -> Brightness does not work) I contacted 
the maintainer of acer-wmi. Here is the content of my mail and his quick 
answer:

Hi Carlos
First, let me thank you for your work on getting Acer laptop working with 
Linux.
Now, since my Debian Squeeze kernel went from 2.6.28 to 2.6.30, backlight 
setting does not work any longer, and the brightness seems to be set at random 
level at boot time. My laptop is an aspire 5715Z.
dmesg gives:
dmesg |grep video
[    7.161248] acer-wmi: Brightness must be controlled by generic video driver
[   27.366381] ACPI Error (video-0537): Current brightness invalid [20090320]

and
dmesg |grep acer
[    7.140188] acer-wmi: Acer Laptop ACPI-WMI Extras
[    7.161248] acer-wmi: Brightness must be controlled by generic video driver

Also, there is no folder named backlight under /sys/devices/acer-wmi/platform/ 
with kernel 2.6.30.

Should you need other information, please fill free to contact me

and the answer

This, and the above messages, mean that the generic ACPI video driver is 
taking control of the backlight, and not acer-wmi (acer-wmi, and most of the 
other laptop specific platform drivers, will let the generic ACPI video driver 
handle brightness, etc, if they are able to). Unfortunately, I'm not that 
familiar with it, so you'd need to talk to the maintainers of that instead.

-Carlos

So, it seems to me that I should investigate toward ACPI video driver. OK, but 
I don't have any idea where to start to be able to give useful information to 
the maintainer of this module (I don't even know how to get the proper name of 
this module). At that point, it's obvious that any help will be most welcome.
Thanks in advance
Thierry