Re: [PATCH v8] pci: prevent putting nvidia GPUs into lower device states on certain intel bridges

[Karol Herbst]

just noticed that the patch title should be changed..

drm/nouveau: prevent putting nvidia GPUs into lower device states on
certain intel bridges

or

drm/nouveau: workaround runpm fail by disabling PCI power management
on certain intel bridges

On Tue, Mar 24, 2020 at 9:29 PM Karol Herbst <kherbst@xxxxxxxxxx> wrote:
>
> Fixes the infamous 'runtime PM' bug many users are facing on Laptops with
> Nvidia Pascal GPUs by skipping said PCI power state changes on the GPU.
>
> Depending on the used kernel there might be messages like those in demsg:
>
> "nouveau 0000:01:00.0: Refused to change power state, currently in D3"
> "nouveau 0000:01:00.0: can't change power state from D3cold to D0 (config
> space inaccessible)"
> followed by backtraces of kernel crashes or timeouts within nouveau.
>
> It's still unkown why this issue exists, but this is a reliable workaround
> and solves a very annoying issue for user having to choose between a
> crashing kernel or higher power consumption of their Laptops.
>
> Signed-off-by: Karol Herbst <kherbst@xxxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: Lyude Paul <lyude@xxxxxxxxxx>
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Cc: Mika Westerberg <mika.westerberg@xxxxxxxxx>
> Cc: linux-pci@xxxxxxxxxxxxxxx
> Cc: linux-pm@xxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: nouveau@xxxxxxxxxxxxxxxxxxxxx
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=205623
> ---
> v2: convert to pci_dev quirk
>     put a proper technical explanation of the issue as a in-code comment
> v3: disable it only for certain combinations of intel and nvidia hardware
> v4: simplify quirk by setting flag on the GPU itself
> v5: restructure quirk to make it easier to add new IDs
>     fix whitespace issues
>     fix potential NULL pointer access
>     update the quirk documentation
> v6: move quirk into nouveau
> v7: fix typos and commit message
> v8: reset the pm_cap field to get rid of changes in pci core (thanks to
>     Bjorn for this idea)
>
>  drivers/gpu/drm/nouveau/nouveau_drm.c | 63 +++++++++++++++++++++++++++
>  drivers/gpu/drm/nouveau/nouveau_drv.h |  2 +
>  2 files changed, 65 insertions(+)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
> index 2cd83849600f..b1beed40e746 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_drm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
> @@ -618,6 +618,64 @@ nouveau_drm_device_fini(struct drm_device *dev)
>         kfree(drm);
>  }
>
> +/*
> + * On some Intel PCIe bridge controllers doing a
> + * D0 -> D3hot -> D3cold -> D0 sequence causes Nvidia GPUs to not reappear.
> + * Skipping the intermediate D3hot step seems to make it work again. This is
> + * probably caused by not meeting the expectation the involved AML code has
> + * when the GPU is put into D3hot state before invoking it.
> + *
> + * This leads to various manifestations of this issue:
> + *  - AML code execution to power on the GPU hits an infinite loop (as the
> + *    code waits on device memory to change).
> + *  - kernel crashes, as all PCI reads return -1, which most code isn't able
> + *    to handle well enough.
> + *
> + * In all cases dmesg will contain at least one line like this:
> + * 'nouveau 0000:01:00.0: Refused to change power state, currently in D3'
> + * followed by a lot of nouveau timeouts.
> + *
> + * In the \_SB.PCI0.PEG0.PG00._OFF code deeper down writes bit 0x80 to the not
> + * documented PCI config space register 0x248 of the Intel PCIe bridge
> + * controller (0x1901) in order to change the state of the PCIe link between
> + * the PCIe port and the GPU. There are alternative code paths using other
> + * registers, which seem to work fine (executed pre Windows 8):
> + *  - 0xbc bit 0x20 (publicly available documentation claims 'reserved')
> + *  - 0xb0 bit 0x10 (link disable)
> + * Changing the conditions inside the firmware by poking into the relevant
> + * addresses does resolve the issue, but it seemed to be ACPI private memory
> + * and not any device accessible memory at all, so there is no portable way of
> + * changing the conditions.
> + * On a XPS 9560 that means bits [0,3] on \CPEX need to be cleared.
> + *
> + * The only systems where this behavior can be seen are hybrid graphics laptops
> + * with a secondary Nvidia Maxwell, Pascal or Turing GPU. It's unclear whether
> + * this issue only occurs in combination with listed Intel PCIe bridge
> + * controllers and the mentioned GPUs or other devices as well.
> + *
> + * documentation on the PCIe bridge controller can be found in the
> + * "7th Generation Intel Processor Families for H Platforms Datasheet Volume 2"
> + * Section "12 PCI Express* Controller (x16) Registers"
> + */
> +
> +static void quirk_broken_nv_runpm(struct pci_dev *pdev)
> +{
> +       struct drm_device *dev = pci_get_drvdata(pdev);
> +       struct nouveau_drm *drm = nouveau_drm(dev);
> +       struct pci_dev *bridge = pci_upstream_bridge(pdev);
> +
> +       if (!bridge || bridge->vendor != PCI_VENDOR_ID_INTEL)
> +               return;
> +
> +       switch (bridge->device) {
> +       case 0x1901:
> +               drm->old_pm_cap = pdev->pm_cap;
> +               pdev->pm_cap = 0;
> +               NV_INFO(drm, "Disabling PCI power management to avoid bug\n");
> +               break;
> +       }
> +}
> +
>  static int nouveau_drm_probe(struct pci_dev *pdev,
>                              const struct pci_device_id *pent)
>  {
> @@ -699,6 +757,7 @@ static int nouveau_drm_probe(struct pci_dev *pdev,
>         if (ret)
>                 goto fail_drm_dev_init;
>
> +       quirk_broken_nv_runpm(pdev);
>         return 0;
>
>  fail_drm_dev_init:
> @@ -736,7 +795,11 @@ static void
>  nouveau_drm_remove(struct pci_dev *pdev)
>  {
>         struct drm_device *dev = pci_get_drvdata(pdev);
> +       struct nouveau_drm *drm = nouveau_drm(dev);
>
> +       /* revert our workaround */
> +       if (drm->old_pm_cap)
> +               pdev->pm_cap = drm->old_pm_cap;
>         nouveau_drm_device_remove(dev);
>  }
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
> index 70f34cacc552..8104e3806499 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_drv.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
> @@ -138,6 +138,8 @@ struct nouveau_drm {
>
>         struct list_head clients;
>
> +       u8 old_pm_cap;
> +
>         struct {
>                 struct agp_bridge_data *bridge;
>                 u32 base;
> --
> 2.25.1
>