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To:     "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
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Subject: RE: [PATCH v2 3/5] PCI/ATS: Skip VF ATS initialization if PF does not
 implement it
Thread-Topic: [PATCH v2 3/5] PCI/ATS: Skip VF ATS initialization if PF does
 not implement it
Thread-Index: AQHVBDBRJWpopWoBg0y/o9UFe62ul6Zersog
Date:   Mon, 6 May 2019 22:35:38 +0000
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> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of
> sathyanarayanan.kuppuswamy@linux.intel.com
> Sent: Monday, May 6, 2019 12:20 PM
> To: bhelgaas@google.com
> Cc: linux-pci@vger.kernel.org; linux-kernel@vger.kernel.org; ashok.raj@intel.com;
> keith.busch@intel.com; sathyanarayanan.kuppuswamy@linux.intel.com
> Subject: [PATCH v2 3/5] PCI/ATS: Skip VF ATS initialization if PF does not implement it
> 
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.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.
...
> +	/*
> +	 * 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.
> +	 */
...

In standardese, "should" means recommended, not required. The PCIe spec uses
"must" for this rule; the comments should match.