於 日，2012-05-06 於 00:09 +0100，Carlos Corbacho 提到：
> On Saturday 05 May 2012 20:18:55 Lee, Chun-Yi wrote:
> > Acer Extensa 5235, TravelMate 5760 and Aspire 5750 laptop have broken _BCM
> > implemenation, the AML code wrote value to EC register but firmware didn't
> > change brighenss.
> >
> > Fortunately, the brightness control works on those machines with vendor
> > mode. So, add this machine to video backlight vendor mode quirk table.
>
> Is there no way we can auto-detect this somehow? Is there something peculiar
> about the broken implementation that we can use to do this detection instead?
>
> -Carlos
>
Unfortunately, I didn't see anyway can auto-detect the broken _BCM
implementation.
On those machines, the _BCM method write the brightness value to a EC
register, and, we make sure the value write success but EC didn't change
the brightness level.
_BCM like this:
Method (_BCM, 1, NotSerialized)
{
Divide (Arg0, 0x0A, Local0, Local1)
Decrement (Local1)
Store (Local1, ^^^LPCB.EC0.BRTS) <=== write to BRTS register
Currently, didn't find good way to know EC doesn't really change the
brightness level.
I think Acer's ODM don't know this issue because on Vista and Windows 7
platform, they changed brightness through WDDM video driver but not
standard acpi method like _BCM. Some ODM only test brightness by human
eyes and they didn't check acpi method should also works.
Microsoft WDDM spec:
http://msdn.microsoft.com/en-us/windows/hardware/gg487382.aspx
Actually, per WDDM spec, they should keep the standard acpi method works
for backward compatibility to XP or any OS doesn't support WDDM.
I face to face told to Acer's PM at last year for this issue, and also
told them should keep the standard acpi methods works fine, he said will
check with ODM. But, finally, I didn't get further response from Acer.
Use a quirk table to set those machines to 'acpi_backlight=vendor' mode
is better then use 'acpi_osi=Linux', so, I hope experts can kindly
accept this patch to acer-wmi driver for those _BCM broken machines.
Thanks a lot!
Joey Lee
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