Re: PCI: Revert "PCI: Add runtime PM support for PCIe ports"

[Lukas Wunner <lukas@wunner.de>]

On Wed, Jan 04, 2017 at 10:09:54PM +0100, Peter Wu wrote:
> [ Help/ideas are welcome, I suspect that these failures to restore power
> on laptops designed for Win8+ all have the same cause, related to some
> unknown interaction between ACPI and PCI. Some links:
> https://bugzilla.kernel.org/show_bug.cgi?id=190861
> https://bugzilla.kernel.org/show_bug.cgi?id=156341 ]

Looking at Kilian's acpidump again I notice that the methods to power
the GPU on or off (GPON / GPOF) are called from two places:

- From the _PS0 and _PS3 methods of the GPU and
- from the _PR3 power resource of the root port above the GPU.

In the former case they're called for pre Windows 2013 or if VDAD is true.
In the latter case they're called unconditionally but GPOF becomes a no-op
in the pre Windows 2013 case.

This means that GPOF would be executed *twice* on Windows 2013+ if VDAD
is true.  I could imagine this to cause issues.

VDAD is at 0x7CE7D018 + 0xEE2 + 6. It's not set in the DSDT.

@Kilian, what do you get if you execute this as root:

dd iflag=skip_bytes,count_bytes skip=$((0x7CE7D018 + 0xEE2 + 6)) count=1 \
  if=/dev/mem 2>/dev/null | hexdump


Another oddity I've noticed is that when calling the Optimus DSM with
the capabilities function number (0x1A, NOUVEAU_DSM_OPTIMUS_CAPS) and
a special argument, it's possible to influence the behaviour of GPOF
(the method to power the GPU off):  GPOF is a no-op unless it's running
on Windows 2013+ or OMPR has value 0x03.  Initially OMPR has value 0x02,
but by setting bits 18 and 19 in the argument given to the capabilities
function, it can be set to 0x3.  After GPOF has finished, OMPR reverts
back to 0x02.  This means that pre Windows 2013, GPOF only has any effect
if the DSM capabilities function is called with an appropriate argument.
The same functionality can be seen in the Clevo P651RA ssdt3/7.  What
confuses me is that the bits are at position 18 and 19, but in
nouveau_switcheroo_optimus_dsm() we're setting bits 0 and 1 as well as
bits 24 and 25?  This may be a dumb question, I'm not familiar with
Optimus, only Macs.


Thanks,

Lukas