Re: [PATCH] ACPI: return first _ADR match for acpi_get_child

[Lekensteyn <lekensteyn@gmail.com>]

On Wednesday 26 December 2012 15:13:00 Rafael J. Wysocki wrote:
> But as far as I can say, there also are _PS0, _PS1 and _PS3 methods under
> PEG0.VGA and there are display devices under it.
_PS0, _PS1 and _PS3 just set _PSC for ACPI. It does interact with any 
hardware. The display adapter use "CADL" (\CADL based on the scope of 
CRT._DCS, not to be confused with \_SB.PCI0.GFX0.CADL (field IGDM)). This field 
is only written in NVIF. It seems to be a display adapter used for a nvidia 
graphics card.

I know that some Lenovo laptops allow you to select Intel / Nvidia / Optimus 
in their BIOS, maybe this PEG0.VGA is used for the nvidia-only setup (lazy 
Lenovo engineers?). Note that this does *not* apply to this IdeaPad Y570 or a 
Lenovo IdeaPad Y470, these laptops force you into the Optimus mode which means 
that you have two graphics cards activated.

> Moreover, it seems to have
> _DOS defined (which PEGP doesn't have), so I'm not really sure we should
> prefer PEG0.PEGP to PEG0.VGA after all?
The code is a subset of what \_SB.PCI0.GFX0._DOS does.
VGA._DOS:

    Store (And (Arg0, 0x07), DSEN)
GFX0._DOS:

    Store (And (Arg0, 0x07), DSEN)
    If (LEqual (And (Arg0, 0x03), Zero)) {
        If (CondRefOf (HDOS)) {
            HDOS ()
        }
    }

> I wonder what PEG0.PEGP and PEG0.VGA are supposed to represent, actually.
PEGP represents the more powerful Nvidia graphics card. GFX0 is the more 
power-aggressive Intel graphics card. VGA... is something useless? A "it 
works, do not touch anything" leftover? There is also a completely useless 
VGA1 device. To quote Linus [1]:

> It's that simple. Don't expect anything else. Firmware is written by
> people who have lost the will to live (why? Because they do firmware
> development for a living), and the only thing keeping them going is
> the drugs. And they're not the "fun" kind of drugs. The end result is
> predictable. In their drug-induced haze, they make a mess.

Regards,
Peter

 [1]: http://lkml.org/lkml/2012/10/21/75