RE: [PATCH v2 3/5] PCI/ATS: Skip VF ATS initialization if PF does not implement it

[Elliott, Robert (Servers)]

> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of
> sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx
> Sent: Monday, May 6, 2019 12:20 PM
> To: bhelgaas@xxxxxxxxxx
> Cc: linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; ashok.raj@xxxxxxxxx;
> keith.busch@xxxxxxxxx; sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx
> Subject: [PATCH v2 3/5] PCI/ATS: Skip VF ATS initialization if PF does not implement it
> 
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> 
> 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.