I tried giving acpi_backlight = vendor . In that case hot key for
brightness control is working. But i think  , it is not calculating
the correct value for brightness because increasing brightness after
maximum level gives blank screen .

 I also had tried 'acpi_backlight = acer_wmi' as the boot parameter
earlier . In that case  , the driver cannot find any acpi_wmi device
(showed error while booting).

By ' ACPI interface' , I mean 'acpi_video0' inside the
/sys/class/backlight. I havn't tried the /sys/class/backlight
interface directly . I will try that also.

Thanks ,

Pradeep Subrahmanion.

On Tue, Mar 13, 2012 at 6:17 PM, Matthew Garrett [off-list ref] wrote:

On Tue, Mar 13, 2012 at 08:09:52AM -0400, Pradeep Subrahmanion wrote:

quoted

Before taking this approach , I had a look at the WMI interface.But I found from acer-acpi site that , the 4730 series
is using new WMI interface which needs to be reverse engineered.
As far as  acpi interface is concerned , by default it is not at all causing any change in brightness.
When 'acpi_osi=Linux' was added to the boot grub config , the brightness control with hot key started to work .
But it was not changing to correct values. Increasing brightness after maximum level gives blank screen.

That page was last updated in 2009. Have you tried the current acer-wmi
code? You'd probably need to pass backlight=vendor if there's a
non-working ACPI interface.

When you say the ACPI interface doesn't work, what do you mean? Have you
tried using the /sys/class/backlight interface directly?

--
Matthew Garrett | mjg59@srcf.ucam.org