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

Jason Gunthorpe
2022-08-30T13:01:44Z

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