On Wed, Aug 24, 2022 at 08:50:19AM +0000, Gupta, Nipun wrote: > [AMD Official Use Only - General] > > > > > -----Original Message----- > > From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> > > Sent: Monday, August 22, 2022 7:00 PM > > To: Gupta, Nipun <Nipun.Gupta@xxxxxxx> > > Cc: 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; saravanak@xxxxxxxxxx; > > Michael.Srba@xxxxxxxxx; mani@xxxxxxxxxx; yishaih@xxxxxxxxxx; > > jgg@xxxxxxxx; 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>; > > jgg@xxxxxxxxxx; Robin Murphy <robin.murphy@xxxxxxx> > > Subject: Re: [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver > > > > [CAUTION: External Email] > > > > On Mon, Aug 22, 2022 at 01:21:47PM +0000, Gupta, Nipun wrote: > > > [AMD Official Use Only - General] > > > > > > > > > > > > > -----Original Message----- > > > > From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> > > > > Sent: Wednesday, August 17, 2022 9:03 PM > > > > To: Gupta, Nipun <Nipun.Gupta@xxxxxxx> > > > > Cc: 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; saravanak@xxxxxxxxxx; > > > > Michael.Srba@xxxxxxxxx; mani@xxxxxxxxxx; yishaih@xxxxxxxxxx; > > > > jgg@xxxxxxxx; 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 Wed, Aug 17, 2022 at 08:35:38PM +0530, Nipun Gupta wrote: > > > > > CDX bus driver manages the scanning and populating FPGA > > > > > based devices present on the CDX bus. > > > > > > > > > > The bus driver sets up the basic infrastructure and fetches > > > > > the device related information from the firmware. These > > > > > devices are registered as platform devices. > > > > > > > > Ick, why? These aren't platform devices, they are CDX devices. Make > > > > them real devices here, don't abuse the platform device interface for > > > > things that are not actually on the platform bus. > > > > > > CDX is a virtual bus (FW based) which discovers FPGA based platform > > > devices based on communication with FW. > > > > virtual busses are fine to have as a real bus in the kernel, no problem > > there. > > > > > These devices are essentially platform devices as these are memory > > mapped > > > on system bus, but having a property that they are dynamically discovered > > > via FW and are rescannable. > > > > If they are dynamically discoverable and rescannable, then great, it's a > > bus in the kernel and NOT a platform device. > > > > > I think your point is correct in the sense that CDX bus is not an actual bus, > > > but a FW based mechanism to discover FPGA based platform devices. > > > > > > Can you kindly suggest us if we should have the CDX platform device > > scanning > > > code as a CDX bus in "drivers/bus/" folder OR have it in "drivers/fpga/" or > > > "drivers/platform/" or which other suitable location? > > > > drivers/cdx/ ? > > I agree that the approach, which is correct should be used, just wanted > to reconfirm as adding a new bus would lead to change in other areas > like SMMU, MSI and VFIO too and we will need vfio-cdx interface for CDX > bus, similar to vfio-platform. > > On another mail Robin and Jason have suggested to use OF_DYNAMIC. > Can you please also let us know in case that is a suited option where we > use OF_DYNAMIC and have our code as part of "drivers/fpga" instead of > using the bus. (something like pseries CPU hotplug is using to add new > CPU platform devices on runtime: > https://elixir.bootlin.com/linux/v5.19.3/source/arch/powerpc/platforms/pseries/hotplug-cpu.c#L534). > We can share the RFC in case you are interested in looking at code flow > using the of_dynamic approach. Please no more abuse of the platform device. If your device can be discovered by scanning a bus, it is not a platform device. greg k-h
