Re: what's a platform device?

[Kumar Gala <galak@kernel.crashing.org>]

On Feb 22, 2006, at 10:39 PM, Greg KH wrote:

> On Wed, Feb 22, 2006 at 03:47:40PM -0600, Kumar Gala wrote:
> > Guys,
> >
> > I was hoping to get your opinion on a question I had.  The  
> > question comes
> > down to what we think a "platform device" is.
> >
> > The situation I have is an FPGA connected over PCI.  The FPGA  
> > implements
> > various device functionality (serial ports, I2C controller, IR,  
> > etc.) as a
> > single PCI device/function.  The FPGA breaks any notion of a true PCI
> > device, it uses PCI as a device interconnect more than anything else.
> >
> > In talking to Greg about this, he suggested I just create a new  
> > bus_type
> > for this similar to what is being done for usb-serial.  As I  
> > started to
> > think about what I wanted ended up being a platform_device plus a  
> > sysfs
> > entry for the MMIO region.
> >
> > So, it seems that a "platform device" is a pretty generic concept  
> > now.  Do
> > you guys thing its acceptable to use a platform device for my  
> > needs or
> > should I create some new bus_type?  Do we have a better definition  
> > of what
> > a platform device is or might be?
>
> Well, your FPGA is a pci device, right?  It's only the devices that  
> hang
> off of it that you are concerned about.  I really think you should  
> make
> your own bus type, as it's not much work, and it would not disturb the
> existing platform devices, which do not know about mmio regions like
> PCI.

Yes, the FPGA is a pci device.

Not sure I follow exactly what you mean by the fact that platform  
devices dont know about mmio regions.  They know about struct  
resource and iomem_resource & ioport_resource.

I think I might be missing something fundamental here.  In  
implementing my own bus_type, I'll end up introducing my own struct  
foobar_device which looked pretty much like struct platform_device.
Then I'll need a set of functions to assign resources, etc.

I got no issue implementing my own bus_type, but I clearly feel like  
I'm missing something here (just not sure what it is :)

- kumar


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