Re: what's a platform device?

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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.

Yes, as they have no "bus" to attach too.  That's why they are there,
they are for devices with no bus, but are merely "raw" memory mapped
devices.

I'm not sure I follow this. How is PCI different? How would "kumar" bus be different?

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 :)

I guess I look at your FPGA as a PCI "bridge" chip, that bridges between
the PCI bus, and your "kumar" bus (for lack of a better name).  Your
devices hang off of that bus, which is attached to the FPGA, which is
attached to the pci bridge, and so on. If you use the platform bus, you
break that link.

Does that make sense?

This makes sense, but you seem to be talking about hierarchy more the functionality. I agree in your description of hierarchy.

I was looking at it from a functional point of view, maybe more from the device view then from the bus. I need a struct device type that contains resources, a name, an id. I'll do matching based on name. From a functional point of view platform does all this.

Based on your description would you say that a platform_device's parent device should always be platform_bus? [I'm getting at the fact that we allow pdev->dev.parent to be set by the caller of platform_device_add].

Hmm, as I think about this further, I think that its more coincidence that the functionality for the "kumar" bus is equivalent to that of the "platform" bus.

Russell probably has other thoughts about this.

Hopefully he'll provide his thoughts :)

- kumar


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