How to describe a device that sits across two busses.

[Daniel Palmer <daniel@0x0f.com>]

Hi all,

I have a driver for a SPI flash controller that I want to mainline
soon and I'm cleaning up the device tree part for it at the moment.

This device has registers that are children in a "simple bus" and a
memory mapped area that is in the soc simple bus because it's not
connected via the same bus as the registers.

Right now I have the driver's node in the soc simple bus like this:

isp: isp@1f001000 {
  compatible = "mstar,msc313-isp";
  reg = <0x1f001000 0x400>,
           <0x1f002c00 0x200>,
           <0x1f002e00 0x200>,
           <0x14000000 0x1000000>;
};

Really the first 3 reg values belong to this simple bus:

riu: bus@1f000000 {
  compatible = "simple-bus";
  reg = <0x1f000000 0x00400000>;
};

Is there a good way to describe this? I think maybe the memory mapped
area should be another node (syscon?) and that should be referenced in
the driver node and the driver node itself nested in the riu simple
bus where the registers are.

Thanks,

Daniel