From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 19 Apr 2017 11:26:52 +0100 From: Lorenzo Pieralisi To: abhijit Cc: linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Subject: Re: Doubt on first access for PCIe device Message-ID: <20170419102652.GA23487@red-moon> References: <50712b3b-2943-0b78-9413-257f33b26c3f@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <50712b3b-2943-0b78-9413-257f33b26c3f@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 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