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SubjectRE: [PATCH 2/4] PCI: quirk AMD/ATI VGA cards to avoid PM reset
Date
> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@redhat.com]
> Sent: Friday, November 21, 2014 1:24 PM
> To: bhelgaas@google.com
> Cc: linux-pci@vger.kernel.org; linux-kernel@vger.kernel.org; Alex
> Williamson; Deucher, Alexander
> Subject: [PATCH 2/4] PCI: quirk AMD/ATI VGA cards to avoid PM reset
>
> Some AMD/ATI GPUs report that they support PM reset (NoSoftRst-) but
> initiating such a reset has no apparent affect on the device. The
> monitor remains sync'd, the framebuffer contents are retained, etc.
> Callers of pci_reset_function() don't necessarily have a way to
> validate whether a reset was effective, so we really want to avoid
> making use of a known non-effective reset. Returning an error in
> such cases appears to be the better option. For users like vfio-pci,
> this allows the driver to escalate to the bus reset interfaces.
>
> If a device lives on the root bus, there's really no further
> escalation path, so we exempt PM reset as potentially better than
> nothing.
>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>

Acked-by: Alex Deucher <alexander.deucher@amd.com>

> ---
>
> drivers/pci/quirks.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 90acb32..561e10d 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -3008,6 +3008,27 @@
> DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_REALTEK, 0x8169,
> DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MELLANOX, PCI_ANY_ID,
> quirk_broken_intx_masking);
>
> +static void quirk_no_pm_reset(struct pci_dev *dev)
> +{
> + /*
> + * A non-effective PM reset may be better than nothing
> + * if we can't do a bus reset
> + */
> + if (!pci_is_root_bus(dev->bus))
> + dev->dev_flags |= PCI_DEV_FLAGS_NO_PM_RESET;
> +}
> +
> +/*
> + * Some AMD/ATI GPUS (HD8570 - Oland) report supporting PM reset via
> D3->D0
> + * transition (NoSoftRst-). This reset mechanims seems to have no effect
> + * whatsoever on the device, even retaining the framebuffer contents and
> + * monitor sync. Advertising this support makes other layers, like VFIO
> + * assume pci_reset_function() is viable for this device. Mark it as
> + * unavailable to skip it when testing reset methods.
> + */
> +DECLARE_PCI_FIXUP_CLASS_HEADER(PCI_VENDOR_ID_ATI, PCI_ANY_ID,
> + PCI_CLASS_DISPLAY_VGA, 8,
> quirk_no_pm_reset);
> +
> #ifdef CONFIG_ACPI
> /*
> * Apple: Shutdown Cactus Ridge Thunderbolt controller.

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