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

[sathyanarayanan kuppuswamy]

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
> >
> > 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

--
Sathyanarayanan Kuppuswamy
Linux kernel developer