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

[Jason Gunthorpe]

On Tue, Aug 30, 2022 at 07:06:12AM +0000, Gupta, Nipun wrote:
> [AMD Official Use Only - General]
> 
> 
> 
> > -----Original Message-----
> > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Sent: Monday, August 29, 2022 9:02 PM
> > To: Gupta, Nipun <Nipun.Gupta@xxxxxxx>
> > Cc: Robin Murphy <robin.murphy@xxxxxxx>; Saravana Kannan
> > <saravanak@xxxxxxxxxx>; Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>;
> > robh+dt@xxxxxxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx; rafael@xxxxxxxxxx;
> > eric.auger@xxxxxxxxxx; alex.williamson@xxxxxxxxxx; cohuck@xxxxxxxxxx;
> > Gupta, Puneet (DCG-ENG) <puneet.gupta@xxxxxxx>;
> > song.bao.hua@xxxxxxxxxxxxx; mchehab+huawei@xxxxxxxxxx;
> > maz@xxxxxxxxxx; f.fainelli@xxxxxxxxx; jeffrey.l.hugo@xxxxxxxxx;
> > Michael.Srba@xxxxxxxxx; mani@xxxxxxxxxx; yishaih@xxxxxxxxxx; linux-
> > kernel@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx;
> > okaya@xxxxxxxxxx; Anand, Harpreet <harpreet.anand@xxxxxxx>; Agarwal,
> > Nikhil <nikhil.agarwal@xxxxxxx>; Simek, Michal <michal.simek@xxxxxxx>;
> > git (AMD-Xilinx) <git@xxxxxxx>
> > 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