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

[Gupta, Nipun]

[AMD Official Use Only - General]



> -----Original Message-----
> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Tuesday, August 30, 2022 6:31 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 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);

This would be removed with the CDX bus model. It is currently here because
we were deliberately trying to use platform bus.

We will be sending out v3 with CDX bus next week.

Thanks,
Nipun

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