Re: Doubt on first access for PCIe device

From: Lorenzo Pieralisi
Date: Mon Apr 24 2017 - 06:01:33 EST


On Mon, Apr 24, 2017 at 11:52:27AM +0530, abhijit wrote:
> Hi Lorenzo,
>
> Yes that's true..
>
> My question is: what if EP function default completer ID means BDF
> has values = 0(meaning B = 0, D = 0, f = 0) and Root complex
> requester ID also has same BDF, that is 0.
>
> Is that valid case as per PCIe standard, as in this case, requester
> ID and completion ID have same BDF?

Read "2.2.9: Completion rules" and you will have your question answered
there ;-)

Lorenzo

>
> Thank you very much for your replies
>
> Regards,
> Abhijit
>
>
> On Friday 21 April 2017 09:29 PM, Lorenzo Pieralisi wrote:
> >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@xxxxxxx> 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