https://bugzilla.kernel.org/show_bug.cgi?id=42833
--- Comment #12 from Lee, Chun-Yi <j...@novell.com> 2012-03-20 03:58:03 ---
(In reply to comment #11)
> (In reply to comment #9)
> > I'm confused by the ACPI brightness control implement on this machine.
> >
> > Method (_BCM, 1, NotSerialized)
> > {
> > If (LEqual (BOWN, Zero))
> > {
> > Store (Subtract (Divide (Arg0, 0x0A, ),
> > One),
> > Local0)
> > Store (Local0, BRTN)
> > Acquire (^^^^LPCB.EC0.MUT1, 0xFFFF)
> > Store (Local0, ^^^^LPCB.EC0.BLVL)
> > Release (^^^^LPCB.EC0.MUT1)
> >
> > If (LEqual (OSYS, 0x03E8))
> > {
> > /* update IGD LBES field in case it's
> > "Linux"
> > */
> > }
> >
> > If (LLess (OSYS, 0x07D6))
> > {
> > /* Need wmi support if it is not Vista or
> > Win7
> > */
> > }
> > }
> > }
> > Does this mean that updating EC0.BLVL can change the backlight in Windows
> > Vista
> > and Win7? Or windows Vista and Win7 doesn't use ACPI backlight control at
> > all?
> >
> > Hi, Lukacs,
> > will you please check
> > 1) if the brightness works when you boot the kernel with both
> > acpi_osi="!Windows 2009" and acpi_osi="!Windows 2006" ?
> > 2) if the brightness works when you boot the kernel with acpi_osi="Linux"?
>
> Both with acpi_osi="!Windows 2009" and with acpi_osi="!Windows 2006" boot the
> system, but the problem still exist.
>
Yes, you are not the first one, that because Acer ODM provide a broken _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.
But,
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.
> Luckily with acpi_osi="Linux" everything works fine just like with
> "acpi_backlight=vendor", however, when the system boots it starts with the
> lowest backlight level.
I prefer "acpi_backlight=vendor" but not acpi_osi="Linux", because ODM didn't
test the code path with acpi_osi="Linux", they always only test Windows
platform.
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