# Re: \[PATCH\] Added backlight driver for Acer Aspire 4736

- From: joeyli \<jlee@suse.com\>
- Date: 2012-03-19 02:03:44 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2012/03/3837624
- Thread: https://ratatoskr.run/linux-fbdev/2012/03/3835160/t.md

```text
於 日，2012-03-18 於 10:40 +0530，Pradeep Subrahmanion 提到：
> 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：
> > > On Wed, Mar 14, 2012 at 11:21 AM, joeyli [ref] wrote:
> > > > 於 三，2012-03-14 於 08:13 +0530，Pradeep Subrahmanion 提到：
> > > >> Hi Joey ,
> > > >>
> > > >> > 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.
> > > >
> > > >> >
> > > >> > Acer machine provide a broken _BCM implementation and they didn't test
> > > >> > it.
> > > >> >
> > > >> > > > > 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
> > > >
> > > > 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.
> > > >
> > > 
> > > >
> > > > 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

OK, thanks for your testing, I will send out patch and add Cc. to you.

> brightness after  maximum level causes blank screen.So I am trying it
> sort it out.
>  
> Thank you , 
> 
> Pradeep Subrahmanion
> 

For the maximum level causes blank screen...

Please kindly help to identify which driver handle the brightness
change, run the following 2 commands:

# echo 5 > /sys/class/backlight/acer-wmi/brightness 
# echo 5 > /sys/class/backlight/intel_backlight/brightness 

Which one works to change brightness on your machine?


Thanks a lot!
Joey Lee

```