[PATCH] powerpc: Add FSL CPM2 device tree node documentation

[Paul Mackerras]

Dan Malek writes:

> I haven't followed the device tree development in detail, but when
> looking at this the only question that comes to mind is wondering
> what this really does to help me.  None of the information provided
> here is variable nor configurable .... except I guess for the internal
> register base address (IMMR), which for some reason has turned
> into a variable which hasn't changed since I did the first kernel port.
> About the only thing that is variable, which is the two different bank
> addresses of the CPM memory that affects the configuration of
> the FCCs in Ethernet mode, isn't reflected here in any way.

I don't know much about the CPM or CPM2, so I don't know precisely why
these bits have been put in.  If the CPM2 is completely unique and is
identical across all possible past and future implementations, then
indeed there isn't a lot of value in putting details about it in the
device tree.  Having details in the device tree becomes useful if:

* there are variants that have different collections of subdevices, or
  subdevices at different offsets, or

* there are common subdevices between CPM and CPM2 (or future CPM*
  devices), potentially with subtle variations in offset, method of
  enabling, etc., or

* there are subdevices in CPM/CPM2 which match some common device
  (e.g. a 16550 uart) for which a generic driver can be used with some
  appropriate configuration.

As I say, I don't know if these points apply to CPM/CPM2 specifically.

Paul.