On Tue, 2009-09-15 at 15:54 +0800, Rafał Miłecki wrote: 
> OK, you provided me fair amount of texts to read :)
> 
> W dniu 15 września 2009 09:43 użytkownik Zhang Rui
> <[email protected]> napisał:
> > And I think it may work for you as well, i.e. two backlight sysfs I/F
> > may co-exist, it's the user space to decide which I/F to use.
> 
> Could you  explain, please, how does work Fn+F5 and Fn+F6 in
> notebooks? I thought it generates some ACPI that kernel identifies as
> backlight up/down and kernel passes it to module registered with:
> backlight_device_register(...)
> is that right?
> 
No...

the hotkey events can be controlled either by ACPI video device or by
ACPI platform specific device, say sony-laptop.
There are also other ways that ACPI is not involved but they're beyond
my scope. :)

If it's controlled via ACPI video device, the ACPI video backlight
control usually works at this time. When hotkey is pressed, an ACPI
notification is sent to ACPI video device, and then the backlight is
changed via ACPI control methods (_BCM/_BCL/_BQC).

If it's controlled in ACPI platform specific way, then the platform
specific driver (e.g. sony-laptop) can catch the event when hotkey is
pressed and invokes the platform specific methods to change the
backlight.

> Then two backlight devices would be a problem, I guess?
> 
I agree. but we don't have any better idea for now. :(

thanks,
rui


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