Hi Pradeep, 

於 二，2012-03-13 於 21:24 -0400，Pradeep Subrahmanion 提到：

On Tue, 2012-03-13 at 13:34 +0000, Matthew Garrett wrote:

quoted

On Tue, Mar 13, 2012 at 06:56:16PM +0530, Pradeep Subrahmanion wrote:

quoted

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 .

Which backlight device appears then?

'intel_backlight' appears when i gave option acpi_backlight = vendor. Writing to /sys/class/backlight/intel_backlight/brightness

does not cause any change in brightness.

The above command not work, that means EC didn't change backlight
value:

Method (_BCM, 1, NotSerialized)
{
    Divide (Arg0, 0x0A, Local0, Local1)
    Decrement (Local1)
    Store (Local1, ^^^^LPC.EC0.BRTS)    <== write backlight value to EC
register
}

Per my understood, EC firmware should change brightness but didn't do
that, another
way is touch i915 register in _BCM.

Acer machine provide a broken _BCM implementation and they didn't test
it.

quoted

quoted

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.

So writing values into /sys/class/backlight/acpi_video0/brightness does 
nothing?

No change in value when writing
to /sys/class/backlight/acpi_video0/brightness.

Another thing is that when i did boot with acpi_backlight = 'acer_wmi' ,
in new kernel (3.3.0-rc7) , it shows following messages , 

[    8.350825] wmi: Mapper loaded
[   10.363975] acer_wmi: Acer Laptop ACPI-WMI Extras
[   10.396186] acer_wmi: Function bitmap for Communication Device: 0x91
[   10.396385] acer_wmi: Brightness must be controlled by generic video
driver

Also there was no interface inside /sys/class/backlight for acer_wmi. 

Yes, acer_wmi support backlight control with AMW0 interface, your
machine didn't have AMW0 interface.

Normally, backlight should control by standard acpi interface.

I also tried writing directly to Embedded controller register .But no
change.

The machine has broken _BCM method, because EC should do something after
_BCM changed EC register.

----

Thanks , 

Pradeep Subrahmanion
  

Thanks a lot!
Joey Lee