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

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Message-ID: <99dce715-e83a-72ce-aa01-f388b73c2604@jonmasters.org>
Date:   Wed, 19 Apr 2017 01:00:15 -0400
From:   Jon Masters <jcm@...masters.org>
To:     abhijit <abhijitnaik27@...il.com>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: Doubt on first access for PCIe device

On 04/11/2017 10:15 AM, abhijit wrote:

> 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?

You'll want to read about PCIe enumeration at boot time and how the BIOS
walks the topology to assign these (which an OS may later re-number). In
particular, read about ECAM for configuration. This uses memory mapped
config space read/write accessors that target a memory address space
under the control of the root complex.

Jon.