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

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Date:   Tue, 30 Aug 2022 10:01:29 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
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" <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

On Tue, Aug 30, 2022 at 07:06:12AM +0000, Gupta, Nipun wrote:
> [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 would be alot clearer to see a rfc cdx driver that doesn't have all
the dt,fwnode,of stuff in it and works like PCI does, with a custom
matcher and custom properies instead of trying to co-opt the DT things:

Eg stuff like this make it look like you are building DT nodes:

+	struct property_entry port_props[] = {
+		PROPERTY_ENTRY_STRING("compatible",
+			dev_types[dev_params->dev_type_idx].compat),
+		{ }

+			ret = of_map_id(np, req_id, "iommu-map", "iommu-map-mask",
+					NULL, &dev_params.stream_id);

I still don't understand why FW would be involved, we usually don't
involve FW for PCI..

Jason