linux-kernel - Re: [PATCH] Added backlight driver for Acer Aspire 4736

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Message-ID: <CABNxG=D3y2GQqS1XN=+B0QRScXpufBkPQtP5-SSNEjSavhtW7g@mail.gmail.com>
Date:	Wed, 14 Mar 2012 11:47:09 +0530
From:	Pradeep Subrahmanion <subrahmanion.pradeep@...il.com>
To:	joeyli <jlee@...e.com>
Cc:	Matthew Garrett <mjg@...hat.com>, rpurdie@...ys.net,
	FlorianSchandinat@....de, akpm@...ux-foundation.org,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Added backlight driver for Acer Aspire 4736

On Wed, Mar 14, 2012 at 11:21 AM, joeyli <jlee@...e.com> 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
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