linux-kernel - Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

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Date:   Sat, 8 Apr 2017 09:41:07 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Daniel Drake <drake@...lessm.com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Samuel Sieb <samuel@...b.net>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <jroedel@...e.de>,
        Paul Menzel <pmenzel@...gen.mpg.de>
Subject: Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

On Fri, Apr 07, 2017 at 04:32:18PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> ATS is broken on this hardware and causes IOMMU stalls and
> system failure. Disable ATS on these devices to make them
> usable again with IOMMU enabled.

AMD Stoney Ridge is an x86 CPU + GPU combo and this quirk pertains
to the GPU, right?

In that case the quirk should go to arch/x86.  Paul Menzel (+cc)
has just complained on linux-pci@ that final fixups are taking half
a second, and I think that could be reduced if more efforts were
spent to move arch-specific quirks out of the catch-all in
drivers/pci/quirks.c.

Thanks,

Lukas

> 
> Note that the commit in the Fixes-tag is not buggy, it
> just uncovers the problem in the hardware by increasing
> the ATS-flush rate.
> 
> Fixes: b1516a14657a ('iommu/amd: Implement flush queue')
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  drivers/pci/quirks.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 6736836..7cbe316 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -4634,3 +4634,22 @@ static void quirk_no_aersid(struct pci_dev *pdev)
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x2031, quirk_no_aersid);
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x2032, quirk_no_aersid);
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x2033, quirk_no_aersid);
> +
> +#ifdef CONFIG_PCI_ATS
> +/*
> + * Some devices have a broken ATS implementation causing IOMMU stalls.
> + * Don't use ATS for those devices.
> + */
> +static void quirk_disable_ats(struct pci_dev *pdev)
> +{
> +	/*
> +	 * Set pdev->ats_cap = 0 to make pci_enable_ats() bail out
> +	 * early.
> +	 */
> +	dev_info(&pdev->dev, "QUIRK: Disabling ATS");
> +	pdev->ats_cap = 0;
> +}
> +
> +/* AMD Stoney platform GPU */
> +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_ATI, 0x98e4, quirk_disable_ats);
> +#endif /* CONFIG_PCI_ATS */
> -- 
> 1.9.1
>