linux-kernel - Re: [PATCH v2 3/5] PCI/ATS: Skip VF ATS initialization if PF does not implement it

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Date:   Wed, 29 May 2019 21:53:44 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     sathyanarayanan.kuppuswamy@...ux.intel.com
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...el.com, keith.busch@...el.com
Subject: Re: [PATCH v2 3/5] PCI/ATS: Skip VF ATS initialization if PF does
 not implement it

On Mon, May 06, 2019 at 10:20:05AM -0700, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> If PF does not implement ATS and VF implements/uses it, it might lead to
> runtime issues. Also, as per spec r4.0, sec 9.3.7.8, PF should implement
> ATS if VF implements it. So add additional check to confirm given device
> aligns with the spec.

"might lead to runtime issues" is pretty wishy-washy.  I really don't
want to prevent some device from working merely because it has
something in config space that doesn't follow the spec exactly but we
never touch.

> Cc: Ashok Raj <ashok.raj@...el.com>
> Cc: Keith Busch <keith.busch@...el.com>
> Suggested-by: Ashok Raj <ashok.raj@...el.com>
> Reviewed-by: Keith Busch <keith.busch@...el.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
>  drivers/pci/ats.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index e7a904e347c3..718e6f414680 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -19,6 +19,7 @@
>  void pci_ats_init(struct pci_dev *dev)
>  {
>  	int pos;
> +	struct pci_dev *pdev;
>  
>  	if (pci_ats_disabled())
>  		return;
> @@ -27,6 +28,17 @@ void pci_ats_init(struct pci_dev *dev)
>  	if (!pos)
>  		return;
>  
> +	/*
> +	 * Per PCIe r4.0, sec 9.3.7.8, if VF implements Address Translation
> +	 * Services (ATS) Extended Capability then corresponding PF should
> +	 * also implement it.
> +	 */
> +	if (dev->is_virtfn) {
> +		pdev = pci_physfn(dev);
> +		if (!pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ATS))
> +			return;
> +	}
> +
>  	dev->ats_cap = pos;
>  }
>  
> -- 
> 2.20.1
>