linux-kernel - Re: [PATCH v1 1/2] PCI: ATS: Add function to check ATS page aligned request status.

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Message-ID: <815f2621-fc28-bff4-c300-cce7514cfe71@kernel.org>
Date:   Fri, 8 Feb 2019 23:49:55 -0500
From:   Sinan Kaya <Okaya@...nel.org>
To:     sathyanarayanan.kuppuswamy@...ux.intel.com, bhelgaas@...gle.com,
        joro@...tes.org, dwmw2@...radead.org
Cc:     linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Ashok Raj <ashok.raj@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Keith Busch <keith.busch@...el.com>
Subject: Re: [PATCH v1 1/2] PCI: ATS: Add function to check ATS page aligned
 request status.

On 2/8/2019 8:02 PM, sathyanarayanan kuppuswamy wrote:
>> This means that you should probably have some kind of version check
>> here.
> 
> There is no version field in ATS v1.0 spec. Also, If I follow the 
> history log in PCI spec, I think ATS if first added at v1.2. Please 
> correct me if I am wrong.

v1.2 was incorporated into PCIe spec at that time. However, the ATS spec
is old and there could be some HW that could claim to be ATS compatible.
I know AMD GPUs declare ATS capability.

See this ECN

https://composter.com.ua/documents/ats_r1.1_26Jan09.pdf

You need to validate the version field from ATS capability header to be
1 before reading this register.

See Table 5-1:  ATS Extended Capability Header