linux-kernel - Re: Doubt on first access for PCIe device

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Message-ID: <20170424100159.GA23513@red-moon>
Date:   Mon, 24 Apr 2017 11:01:59 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     abhijit <abhijitnaik27@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: Doubt on first access for PCIe device

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@....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