Re: [PATCH v4] pci: prevent putting nvidia GPUs into lower device states on certain intel bridges

[Karol Herbst <kherbst@redhat.com>]

On Wed, Nov 20, 2019 at 4:15 PM Mika Westerberg
<mika.westerberg@intel.com> wrote:
>
> On Wed, Nov 20, 2019 at 01:11:52PM +0100, Karol Herbst wrote:
> > On Wed, Nov 20, 2019 at 1:09 PM Mika Westerberg
> > <mika.westerberg@intel.com> wrote:
> > >
> > > On Wed, Nov 20, 2019 at 12:58:00PM +0100, Karol Herbst wrote:
> > > > overall, what I really want to know is, _why_ does it work on windows?
> > >
> > > So do I ;-)
> > >
> > > > Or what are we doing differently on Linux so that it doesn't work? If
> > > > anybody has any idea on how we could dig into this and figure it out
> > > > on this level, this would probably allow us to get closer to the root
> > > > cause? no?
> > >
> > > Have you tried to use the acpi_rev_override parameter in your system and
> > > does it have any effect?
> > >
> > > Also did you try to trace the ACPI _ON/_OFF() methods? I think that
> > > should hopefully reveal something.
> > >
> >
> > I think I did in the past and it seemed to have worked, there is just
> > one big issue with this: it's a Dell specific workaround afaik, and
> > this issue plagues not just Dell, but we've seen it on HP and Lenovo
> > laptops as well, and I've heard about users having the same issues on
> > Asus and MSI laptops as well.
>
> Maybe it is not a workaround at all but instead it simply determines
> whether the system supports RTD3 or something like that (IIRC Windows 8
> started supporting it). Maybe Dell added check for Linux because at that
> time Linux did not support it.
>

the point is, it's not checking it by default, so by default you still
run into the windows 8 codepath.

> In case RTD3 is supported it invokes LKDS() which probably does the L2
> or L3 entry and this is for some reason does not work the same way in
> Linux than it does with Windows 8+.
>
> I don't remember if this happens only with nouveau or with the
> proprietary driver as well but looking at the nouveau runtime PM suspend
> hook (assuming I'm looking at the correct code):
>
> static int
> nouveau_pmops_runtime_suspend(struct device *dev)
> {
>         struct pci_dev *pdev = to_pci_dev(dev);
>         struct drm_device *drm_dev = pci_get_drvdata(pdev);
>         int ret;
>
>         if (!nouveau_pmops_runtime()) {
>                 pm_runtime_forbid(dev);
>                 return -EBUSY;
>         }
>
>         nouveau_switcheroo_optimus_dsm();
>         ret = nouveau_do_suspend(drm_dev, true);
>         pci_save_state(pdev);
>         pci_disable_device(pdev);
>         pci_ignore_hotplug(pdev);
>         pci_set_power_state(pdev, PCI_D3cold);
>         drm_dev->switch_power_state = DRM_SWITCH_POWER_DYNAMIC_OFF;
>         return ret;
> }
>
> Normally PCI drivers leave the PCI bus PM things to PCI core but here
> the driver does these. So I wonder if it makes any difference if we let
> the core handle all that:
>
> static int
> nouveau_pmops_runtime_suspend(struct device *dev)
> {
>         struct pci_dev *pdev = to_pci_dev(dev);
>         struct drm_device *drm_dev = pci_get_drvdata(pdev);
>         int ret;
>
>         if (!nouveau_pmops_runtime()) {
>                 pm_runtime_forbid(dev);
>                 return -EBUSY;
>         }
>
>         nouveau_switcheroo_optimus_dsm();
>         ret = nouveau_do_suspend(drm_dev, true);
>         pci_ignore_hotplug(pdev);
>         drm_dev->switch_power_state = DRM_SWITCH_POWER_DYNAMIC_OFF;
>         return ret;
> }
>
> and similar for the nouveau_pmops_runtime_resume().
>

yeah, I tried that at some point and it didn't help either. The reason
we call those from inside Nouveau is to support systems pre _PR where
nouveau invokes custom _DSM calls on its own. We could potentially
check for that though.