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

[Peter Wu]

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.

> 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.
-- 
Kind regards,
Peter Wu
https://lekensteyn.nl