[Nouveau] [Bug 98398] Acer Aspire V7-582PG (Haswell, GTX 750M) fails to power off GPU with runtime PM

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98398

--- Comment #11 from Peter Wu <peter at lekensteyn.nl> ---
So 4.7 and before used the "DSM" method on runtime-suspend:
- \_SB.PCI0.RP05.PEGP._DSM would be invoked to enable Optimus
- \_SB.PCI0.RP05.PEGP._PS3 is then invoked which would enter D3cold
(note, this method is still used in 4.8 on older laptops or with the
pcie_pm_port=off kernel option)

Since 4.8, _DSM is not called anymore by nouveau (when support from the PCI
core is detected) and this sequence should instead happen:
- \_SB.PCI0.RP05.PEGP._PS3 (does nothing besides updating _STA)
- PCIe core removes power for the PCIe port since all its children are in
  D3 and are willing to transition to D3cold. It does so by invoking
  \NVP3._OFF (where \NVP3 is the power resource from \_SB.PCI0.RP05._PR3)

That is how I think it should work in theory, but on Ricks laptop running
4.8.4,
/sys/bus/devices/0000:1c.4/firmware_node/ does not have power_resources_D0
devices (which I do have on my own laptop for 0000:01:0).

The SSDT1 of Rick's Acer laptop shows this structure:

    If (\_OSI ("Windows 2013"))
    {
        Scope (\_SB.PCI0.RP05)
        {
        //...
            Name (_PR0, Package (0x01)  // _PR0: Power Resources for D0
            {
                NVP3
            })
            Name (_PR2, Package (0x01)  // _PR2: Power Resources for D2
            {
                NVP2
            })
            Name (_PR3, Package (0x01)  // _PR3: Power Resources for D3hot
            {
                NVP3
            })
            // ...
            Method (_PS0, 0, NotSerialized)  // _PS0: Power State 0
            {
            }

            Method (_PS3, 0, NotSerialized)  // _PS3: Power State 3
            {
            }
        }

        Name (MSD3, Zero)
        PowerResource (NVP3, 0x00, 0x0000)
        {
            Name (_STA, One)  // _STA: Status
            // ...

            Method (_ON, 0, NotSerialized)  // _ON_: Power On
            {
                // ...
            }

            Method (_OFF, 0, NotSerialized)  // _OFF: Power Off
            {
                // ...
            }
        }

The dmesg does show "ACPI: Power Resource [NVP3] (on)", so I guess that the
methods are found. It is a mystery to me why the "power_resources_Dx" files are
not created, possibly breaking PM.

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