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

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Date:   Mon, 29 Aug 2022 04:49:21 +0000
From:   "Gupta, Nipun" <Nipun.Gupta@....com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Robin Murphy <robin.murphy@....com>
CC:     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: Friday, August 26, 2022 5:38 AM
> To: Robin Murphy <robin.murphy@....com>
> Cc: Saravana Kannan <saravanak@...gle.com>; Greg KH
> <gregkh@...uxfoundation.org>; Gupta, Nipun <Nipun.Gupta@....com>;
> 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 Thu, Aug 25, 2022 at 08:57:49PM +0100, Robin Murphy wrote:
> 
> > To my mind, it would definitely help to understand if this is a *real*
> > discoverable bus in hardware, i.e. does one have to configure one's device
> > with some sort of CDX wrapper at FPGA synthesis time, that then physically
> > communicates with some sort of CDX controller to identify itself once
> > loaded; or is it "discoverable" in the sense that there's some firmware on
> > an MCU controlling what gets loaded into the FPGA, and software can query
> > that and get back whatever precompiled DTB fragment came bundled with the
> > bitstream, i.e. it's really more like fpga-mgr in a fancy hat?
> 
> So much of the IP that you might want to put in a FPGA needs DT, I
> don't thing a simplistic AMBA like discoverable thing would be that
> interesting.
> 
> Think about things like FPGA GPIOs being configured as SPI/I2C, then
> describing the board config of SPI/I2C busses, setting up PCI bridges,
> flash storage controllers and all sorts of other typically embedded
> stuff that really relies on DT these days.
> 
> It would be nice if Xilinx could explain more about what environment
> this is targetting. Is it Zynq-like stuff?

This solution is not targeted for GPIO/SPI or I2C like devices which rely on
DT, but would have PCI like network/storage devices. It is not targeted for
Zynq platform. I have added more details on other mail. Please refer to
that mail.

Thanks,
Nipun

> 
> Jason