debugging backlight issues

[David Tombs]

On 06/17/2010 02:50 PM, Kamal Mostafa wrote:
> On Thu, 2010-06-17 at 11:05 -0400, David Tombs wrote:
> 
>>> param "acpi.brightness_switch_enabled=0" 
>>
>> Do you know of any documentation for this?
> 
> No, I just observed it in the source -- It is present in Ubuntu kernel
> source (Lucid onward, at least) but you're right, it does not in fact
> disable acpi control of the backlight after all.
> 
> As Stefan recommended, acpi_backlight=vendor might be interesting to
> you.  I find that it does disable acpi's control of the backlight on one
> of my laptops but has no effect on another laptop.  (The laptop where it
> has no effect is likely already using a vendor-specific backlight
> driver.)
> 
>  -Kamal

Thanks Kamal,

I'm now trying to debug an issue where the backlight keys work but not
properly (jumping steps, etc.). I think it's an issue where single
keypresses are getting routed to multiple places and therefore the
brightness is adjusted multiple times.

So, I ask now, what are the different routes in which brightness will
get adjusted? I'm thinking there are three:

1) Pure hw, like we discussed before.

2) Pure kernel ACPI, which brightness_switch_enabled=0 would turn off.

3) Userspace power manager like gnome-power-manager, which can be turned
off by killing the process.

Is this correct?

Thanks in advance,
David