linux-kernel - RE: [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver

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Date:   Tue, 30 Aug 2022 07:06:12 +0000
From:   "Gupta, Nipun" <Nipun.Gupta@....com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Robin Murphy <robin.murphy@....com>,
        Saravana Kannan <saravanak@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "Gupta, Puneet (DCG-ENG)" <puneet.gupta@....com>,
        "song.bao.hua@...ilicon.com" <song.bao.hua@...ilicon.com>,
        "mchehab+huawei@...nel.org" <mchehab+huawei@...nel.org>,
        "maz@...nel.org" <maz@...nel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "jeffrey.l.hugo@...il.com" <jeffrey.l.hugo@...il.com>,
        "Michael.Srba@...nam.cz" <Michael.Srba@...nam.cz>,
        "mani@...nel.org" <mani@...nel.org>,
        "yishaih@...dia.com" <yishaih@...dia.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "okaya@...nel.org" <okaya@...nel.org>,
        "Anand, Harpreet" <harpreet.anand@....com>,
        "Agarwal, Nikhil" <nikhil.agarwal@....com>,
        "Simek, Michal" <michal.simek@....com>,
        "git (AMD-Xilinx)" <git@....com>
Subject: RE: [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver

[AMD Official Use Only - General]



> -----Original Message-----
> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Monday, August 29, 2022 9:02 PM
> To: Gupta, Nipun <Nipun.Gupta@....com>
> Cc: Robin Murphy <robin.murphy@....com>; Saravana Kannan
> <saravanak@...gle.com>; Greg KH <gregkh@...uxfoundation.org>;
> robh+dt@...nel.org; krzysztof.kozlowski+dt@...aro.org; rafael@...nel.org;
> eric.auger@...hat.com; alex.williamson@...hat.com; cohuck@...hat.com;
> Gupta, Puneet (DCG-ENG) <puneet.gupta@....com>;
> song.bao.hua@...ilicon.com; mchehab+huawei@...nel.org;
> maz@...nel.org; f.fainelli@...il.com; jeffrey.l.hugo@...il.com;
> Michael.Srba@...nam.cz; mani@...nel.org; yishaih@...dia.com; linux-
> kernel@...r.kernel.org; devicetree@...r.kernel.org; kvm@...r.kernel.org;
> okaya@...nel.org; Anand, Harpreet <harpreet.anand@....com>; Agarwal,
> Nikhil <nikhil.agarwal@....com>; Simek, Michal <michal.simek@....com>;
> git (AMD-Xilinx) <git@....com>
> Subject: Re: [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver
> 
> [CAUTION: External Email]
> 
> On Mon, Aug 29, 2022 at 04:49:02AM +0000, Gupta, Nipun wrote:
> 
> > Devices are created in FPFGA with a CDX wrapper, and CDX
> controller(firmware)
> > reads that CDX wrapper to find out new devices. Host driver then interacts
> with
> > firmware to find newly discovered devices. This bus aligns with PCI
> infrastructure.
> > It happens to be an embedded interface as opposed to off-chip
> connection.
> 
> Why do you need an FW in all of this?
> 
> And why do you need DT at all?

We need DT to describe the CDX controller only, similar to
how PCI controller is described in DT. PCI devices are
never enumerated in DT. All children are to be dynamically
discovered. 

Children devices do not require DT as they will be discovered
by the bus driver.

Like PCI controller talks to PCI device over PCI spec defined channel,
we need CDX controller to talk to CDX device over a custom
defined (FW managed) channel.

> 
> It is still not clear
> 
> Jason