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Date:   Wed, 16 Oct 2019 14:14:24 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Karol Herbst <kherbst@redhat.com>
Cc:     linux-kernel@vger.kernel.org, Lyude Paul <lyude@redhat.com>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Mika Westerberg <mika.westerberg@intel.com>,
        linux-pci@vger.kernel.org, linux-pm@vger.kernel.org,
        dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org
Subject: Re: [PATCH v3] pci: prevent putting nvidia GPUs into lower device
 states on certain intel bridges
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On Wed, Oct 16, 2019 at 04:44:49PM +0200, Karol Herbst wrote:
> Fixes state transitions of Nvidia Pascal GPUs from D3cold into higher device
> states.
> 
> 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
> 
> Signed-off-by: Karol Herbst <kherbst@redhat.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> Cc: Mika Westerberg <mika.westerberg@intel.com>
> Cc: linux-pci@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: nouveau@lists.freedesktop.org
> ---
>  drivers/pci/pci.c    | 11 ++++++++++
>  drivers/pci/quirks.c | 52 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pci.h  |  1 +
>  3 files changed, 64 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b97d9e10c9cc..8e056eb7e6ff 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -805,6 +805,13 @@ static inline bool platform_pci_bridge_d3(struct pci_dev *dev)
>  	return pci_platform_pm ? pci_platform_pm->bridge_d3(dev) : false;
>  }
>  
> +static inline bool parent_broken_child_pm(struct pci_dev *dev)
> +{
> +	if (!dev->bus || !dev->bus->self)
> +		return false;
> +	return dev->bus->self->broken_nv_runpm && dev->broken_nv_runpm;
> +}
> +
>  /**
>   * pci_raw_set_power_state - Use PCI PM registers to set the power state of
>   *			     given PCI device
> @@ -850,6 +857,10 @@ static int pci_raw_set_power_state(struct pci_dev *dev, pci_power_t state)
>  	   || (state == PCI_D2 && !dev->d2_support))
>  		return -EIO;
>  
> +	/* check if the bus controller causes issues */
> +	if (state != PCI_D0 && parent_broken_child_pm(dev))
> +		return 0;
> +
>  	pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
>  
>  	/*
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 44c4ae1abd00..c2f20b745dd4 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -5268,3 +5268,55 @@ static void quirk_reset_lenovo_thinkpad_p50_nvgpu(struct pci_dev *pdev)
>  DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_NVIDIA, 0x13b1,
>  			      PCI_CLASS_DISPLAY_VGA, 8,
>  			      quirk_reset_lenovo_thinkpad_p50_nvgpu);
> +
> +/*
> + * Some Intel PCIe bridges cause devices to disappear from the PCIe bus after
> + * those were put into D3cold state if they were put into a non D0 PCI PM
> + * device state before doing so.
> + *
> + * This leads to various issue different issues which all manifest differently,
> + * but have the same root cause:
> + *  - AIML code execution hits an infinite loop (as the coe waits on device
> + *    memory to change).
> + *  - kernel crashes, as all pci reads return -1, which most code isn't able
> + *    to handle well enough.
> + *  - sudden shutdowns, as the kernel identified an unrecoverable error after
> + *    userspace tries to access the GPU.
> + *
> + * 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.
> + *
> + * ACPI code writes bit 0x80 to the not documented PCI register 0x248 of the
> + * PCIe bridge controller in order to power down the GPU.
> + * Nonetheless, there are other code paths inside the ACPI firmware which use
> + * other registers, which seem to work fine:
> + *  - 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.
> + *
> + * The only systems where this behavior can be seen are hybrid graphics laptops
> + * with a secondary Nvidia Pascal GPU. It cannot be ruled out that this issue
> + * only occurs in combination with listed Intel PCIe bridge controllers and
> + * the mentioned GPUs or if it's only a hw bug in the bridge controller.
> + *
> + * But because this issue was NOT seen on laptops with an Nvidia Pascal GPU
> + * and an Intel Coffee Lake SoC, there is a higher chance of there being a bug
> + * in the bridge controller rather than in the GPU.
> + *
> + * This issue was not able to be reproduced on non laptop systems.
> + */
> +
> +static void quirk_broken_nv_runpm(struct pci_dev *dev)
> +{
> +	dev->broken_nv_runpm = 1;

Can you use the existing PCI_DEV_FLAGS_NO_D3 flag for this instead of
adding a new flag?

I would put the parent_broken_child_pm() logic here, if possible,
e.g., something like:

  struct pci_dev *bridge = pci_upstream_bridge(dev);

  if (bridge &&
      bridge->vendor == PCI_VENDOR_ID_INTEL && bridge->device == 0x1901)
	dev->dev_flags |= PCI_DEV_FLAGS_NO_D3;

> +}
> +DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_NVIDIA, PCI_ANY_ID,
> +			      PCI_BASE_CLASS_DISPLAY, 16,
> +			      quirk_broken_nv_runpm);
> +/* kaby lake */
> +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, 0x1901,
> +			quirk_broken_nv_runpm);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index ac8a6c4e1792..903a0b3a39ec 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -416,6 +416,7 @@ struct pci_dev {
>  	unsigned int	__aer_firmware_first_valid:1;
>  	unsigned int	__aer_firmware_first:1;
>  	unsigned int	broken_intx_masking:1;	/* INTx masking can't be used */
> +	unsigned int	broken_nv_runpm:1;	/* some combinations of intel bridge controller and nvidia GPUs break rtd3 */
>  	unsigned int	io_window_1k:1;		/* Intel bridge 1K I/O windows */
>  	unsigned int	irq_managed:1;
>  	unsigned int	has_secondary_link:1;
> -- 
> 2.21.0
>