linux-kernel - RE: [PATCH 2/4] PCI: quirk AMD/ATI VGA cards to avoid PM reset

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Date:	Fri, 21 Nov 2014 19:00:32 +0000
From:	"Deucher, Alexander" <Alexander.Deucher@....com>
To:	Alex Williamson <alex.williamson@...hat.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>
CC:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/4] PCI: quirk AMD/ATI VGA cards to avoid PM reset

> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@...hat.com]
> Sent: Friday, November 21, 2014 1:24 PM
> To: bhelgaas@...gle.com
> Cc: linux-pci@...r.kernel.org; linux-kernel@...r.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@...hat.com>
> Cc: Alex Deucher <alexander.deucher@....com>

Acked-by: Alex Deucher <alexander.deucher@....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.