Re: [net-next 1/3] ice: Initialize and register platform device to provide RDMA

[Jason Gunthorpe <jgg@mellanox.com>]

On Thu, Jul 04, 2019 at 03:46:12PM +0200, Greg KH wrote:
> On Thu, Jul 04, 2019 at 12:48:29PM +0000, Jason Gunthorpe wrote:
> > On Thu, Jul 04, 2019 at 02:42:47PM +0200, Greg KH wrote:
> > > On Thu, Jul 04, 2019 at 12:37:33PM +0000, Jason Gunthorpe wrote:
> > > > On Thu, Jul 04, 2019 at 02:29:50PM +0200, Greg KH wrote:
> > > > > On Thu, Jul 04, 2019 at 12:16:41PM +0000, Jason Gunthorpe wrote:
> > > > > > On Wed, Jul 03, 2019 at 07:12:50PM -0700, Jeff Kirsher wrote:
> > > > > > > From: Tony Nguyen <anthony.l.nguyen@intel.com>
> > > > > > > 
> > > > > > > The RDMA block does not advertise on the PCI bus or any other bus.
> > > > > > > Thus the ice driver needs to provide access to the RDMA hardware block
> > > > > > > via a virtual bus; utilize the platform bus to provide this access.
> > > > > > > 
> > > > > > > This patch initializes the driver to support RDMA as well as creates
> > > > > > > and registers a platform device for the RDMA driver to register to. At
> > > > > > > this point the driver is fully initialized to register a platform
> > > > > > > driver, however, can not yet register as the ops have not been
> > > > > > > implemented.
> > > > > > 
> > > > > > I think you need Greg's ack on all this driver stuff - particularly
> > > > > > that a platform_device is OK.
> > > > > 
> > > > > A platform_device is almost NEVER ok.
> > > > > 
> > > > > Don't abuse it, make a real device on a real bus.  If you don't have a
> > > > > real bus and just need to create a device to hang other things off of,
> > > > > then use the virtual one, that's what it is there for.
> > > > 
> > > > Ideally I'd like to see all the RDMA drivers that connect to ethernet
> > > > drivers use some similar scheme.
> > > 
> > > Why?  They should be attached to a "real" device, why make any up?
> > 
> > ? A "real" device, like struct pci_device, can only bind to one
> > driver. How can we bind it concurrently to net, rdma, scsi, etc?
> 
> MFD was designed for this very problem.
> 
> > > > This is for a PCI device that plugs into multiple subsystems in the
> > > > kernel, ie it has net driver functionality, rdma functionality, some
> > > > even have SCSI functionality
> > > 
> > > Sounds like a MFD device, why aren't you using that functionality
> > > instead?
> > 
> > This was also my advice, but in another email Jeff says:
> > 
> >   MFD architecture was also considered, and we selected the simpler
> >   platform model. Supporting a MFD architecture would require an
> >   additional MFD core driver, individual platform netdev, RDMA function
> >   drivers, and stripping a large portion of the netdev drivers into
> >   MFD core. The sub-devices registered by MFD core for function
> >   drivers are indeed platform devices.  
> 
> So, "mfd is too hard, let's abuse a platform device" is ok?
> 
> People have been wanting to do MFD drivers for PCI devices for a long
> time, it's about time someone actually did the work for it, I bet it
> will not be all that complex if tiny embedded drivers can do it :)

Okay, sounds like a NAK to me. I'll drop these patches from the RDMA
patchworks and Jeff can work through the MFD stuff first.

Jason