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SubjectRe: [PATCH v1 1/2] PCI: ATS: Add function to check ATS page aligned request status.

On 2/11/19 11:15 AM, Raj, Ashok wrote:
> On Fri, Feb 08, 2019 at 11:49:55PM -0500, Sinan Kaya wrote:
>> 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.
> It seems rather odd we have to check for ATS version.
> I always assumed unspecified bits (Reserved) must be 0. We only check
> this if ATS is enabled, and this particular bit wasn't given away for another
> feature.
> Is it really required to check for ATS version before consuming this?
If the version check is required then, it needs to be added before
reading "Invalidate Queue Depth" value as well.
>> See this ECN
>> 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

Sathyanarayanan Kuppuswamy
Linux kernel developer

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