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SubjectRe: Doubt on first access for PCIe device
On Fri, Apr 21, 2017 at 03:33:45PM +0530, abhijit naik wrote:
> Hi Lorenzo,
> Thank you very much for reply.
> As you mentioned I noted that, "If a Function must generate a Completion
> prior to the initial device Configuration Write Request, 0's must be
> entered into the Bus Number and Device Number fields"
> By above statement this means that completion ID will be 0x0000. For the
> first device on any bus, device number will be 0 and function number will
> be 0.
> Isn't completer (for configuration read) packet will be addressing itself
> instead of root complex with bus, device and function number 0?

I don't understand what you are asking. The completion (containing
the read data) is routed back to the initiator via ID (of the requester)
routing.

2.2.4.2
2.2.9

Lorenzo

> On Wed, Apr 19, 2017 at 3:56 PM, Lorenzo Pieralisi
> <lorenzo.pieralisi@arm.com> wrote:
>
> On Tue, Apr 11, 2017 at 07:45:40PM +0530, abhijit wrote:
> >
> > Hi All,
> >
> > I was referring Linux code for PCIe enumeration and I have one doubt
> > w.r.t to very first operation that must be done on device.
> >
> > Currently while scanning for device, we directly read vendor ID from
> > device. But PCIE base specification
> > "CB-PCI_Express_Base_4.0r0.7_November-11-2016.pdf" section 2.2.6.2
> > specifies that,
> >
> > "Functions must capture the Bus and Device Numbers supplied with all
> > Type 0 Configuration Write Requests completed by the Function and
> > supply these numbers in the Bus and Device Number fields of the
> > Requester ID for all Requests initiated by the Device/Function."
>
> Please note:
> "for all Requests initiated by the Device/Function".
> ^^^^^^^^^
> > Here I am assuming, the completer ID will be device number and
> > function number that will eventually programmed in to device. In
> > that case, my question is, without first write, how read
> > request(VENDOR ID read) is serviced/routed?
>
> That's not initiated by the endpoint device, it is routed by
> requester ID, which is the requester ID of the configuration
> request - ie master (ie root complex) requester ID.
>
> Read 2.2.9 - Completion rules
>
> HTH,
> Lorenzo
>
> --
> Best wishes,
> Abhijit Naik

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