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

- From: Pradeep Subrahmanion \<hidden\>
- Date: 2012-03-14 02:43:57 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2012/03/3835544
- Thread: https://ratatoskr.run/linux-fbdev/2012/03/3835160/t.md

```text
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 ? 
> 
> 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

```