Re: [Nouveau] [PATCH 4/4] drm/nouveau/acpi: fix lockup with PCIe runtime PM

[Lukas Wunner <lukas@wunner.de>]

On Wed, Jun 01, 2016 at 06:51:51PM +0200, Peter Wu wrote:
> On Tue, May 31, 2016 at 02:20:26PM +0200, Lukas Wunner wrote:
> > On Mon, May 30, 2016 at 06:13:51PM +0200, Peter Wu wrote:
> > > Do you have any suggestions for the case where the pcieport driver
> > > refuses to put the bridge in D3 (because the BIOS is too old)? In that
> > > case the nouveau driver needs to fallback to the DSM method (but not
> > > when runtime PM is deliberately disabled by writing control=on).
> > 
> > The BIOS cut-off date is meant to avoid issues when suspending ports
> > on older chipsets. However if the port is used for an Optimus GPU
> > and we can clearly identify that, and there's a _PR3 method provided,
> > it's probably safe to say that the port is *intended* to be suspended.
> > 
> > So you may want to consider amending pci_bridge_d3_possible() to
> > allow D3 for such ports regardless of the BIOS date, as I've done
> > for Thunderbolt in this commit:
> > https://github.com/l1k/linux/commit/3cb8549cd4e5
> 
> Then we have heuristics based on BIOS year, on whether it is TB or not,
> and next to it whether it is an Optimus laptop? Maybe the PCI core needs
> to export a function that allows drivers to override the detection if
> this becomes more common.

Well I consider the TB and Optimus whitelisting as a stop-gap until
the BIOS date is lowered. Rafael wrote:

    Some time around when machines with Windows 10 started to ship should be
    relatively safe.
    I guess we can just pick a reasonable date in the initial patch and then
    try to move it back to the past subsequently and see if that breaks things
    for anyone.

Source: http://permalink.gmane.org/gmane.linux.power-management.general/75133

> 
> > Not sure how to uniquely identify such ports though. Perhaps check
> > if there's a device in slot 0 below the port which has
> > 	(pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY &&
> > 	(pdev->vendor == PCI_VENDOR_ID_NVIDIA ||
> > 	 pdev->vendor == PCI_VENDOR_ID_ATI)
> 
> Seems fragile, there are desktop setups satisfying this match.

Of course, I didn't mean this to be used as is, you'd have to augment
this with checks e.g. for presence of _PR3 and (if possible) Optimus,
but I'm not familiar enough with Optimus to write down working code
for it, I'm only familiar with apple-gmux switching.

Best regards,

Lukas