On Thu, 2012-03-15 at 16:05 +0800, joeyli wrote:

Hi Pradeep, 

於 三，2012-03-14 於 11:47 +0530，Pradeep Subrahmanion 提到：

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On Wed, Mar 14, 2012 at 11:21 AM, joeyli [off-list ref] wrote:

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於 三，2012-03-14 於 08:13 +0530，Pradeep Subrahmanion 提到：

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Hi Joey ,

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

  how do we do this ? you mean change the _BCM implementation ?

"BIOS guy" should do something like this:

 Method (AINT, 2, NotSerialized)
{
...
       If (LEqual (Arg0, One))
       {
           Store (Divide (Multiply (Arg1, 0xFF), 0x64, ), BCLP)
           Or (BCLP, 0x80000000, BCLP)         <== touch BCLP register
           Store (0x02, ASLC)
       }

   Method (_BCM, 1, NotSerialized)
   {
       If (LAnd (LGreaterEqual (Arg0, Zero), LLessEqual (Arg0, 0x64)))
       {
           AINT (One, Arg0)     <== call AINT method
           Store (Arg0, BRTL)
       }
   }


Just for reference, they should do that when EC didn't wire to
backlight.

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

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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.

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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

Why they didn't find _BCM not work?

My guess is:

Because the backlight control is through WDDM driver on Windows platform
but not through standard ACPI method _BCM. They only test Windows
platform, so, they didn't find _BCM broken.

And, they also didn't really follow Microsoft WDDM spec:

 http://msdn.microsoft.com/en-us/windows/hardware/gg487382.aspx

Per spec,
ODM should keep _BCM works fine for any other OS didn't support WDDM
driver, but they didn't.

At last year, I told Acer PM one time for this issue, they said will
check but finally didn't response me.

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Thanks
Joey Lee

So touching the PCI LBB register is the only feasible solution now
(even though it may not be a clean  method) ?

Thanks,
Pradeep Subrahmanion

That will be better leave LBB register only touched by i915 driver.

If 'acpi_backlight=vendor' works to you, maybe we can add a quirk to
video_detect.c. 
You can try the following patch.

Thanks . I tried your patch .acpi_backlight=vendor allows me to control
brightness with hot key.But there are problems with it like increasing
brightness after  maximum level causes blank screen.So I am trying it
sort it out.
 
Thank you , 

Pradeep Subrahmanion