PowerPC architecture directory layout

[Rafal Jaworowski]

Hi Peter,
we're in the process of porting FreeBSD 6.1 to the Freescale MPC85555 
embedded PowerPC platform. This is PowerQUICC3 integrated telecom 
controller based on the e500 (Book E compliant) core, which is different 
in some important aspects from the "traditional" PowerPC family (AIM).

We'd like to get our port integrated into the FreeBSD source tree 
eventually to mark the start of bringing embedded PowerPC support to the 
project.

There are some general issues we identified and we'd like to discuss:

Current FreeBSD/powerpc port is deeply entangled with OF and Mac 
dependencies: when adding support for a new architecture variant one is 
faced with sys/powerpc/powerpc which is the low-level stuff, quite often 
strictly OF/Mac-oriented.

What would be the strategy for adding a new sub-arch within PowerPC as 
in current shape it's not very extensible and prepared for such 
addition? Our initial thoughts and approach was splitting out the 
existing low-level code into the following hierarchy:

sys/powerpc/powerpc        - files common to all PowerPC variants
sys/powerpc/aim            - specific to "traditional" PowerPC specs 
(most of present sys/powerpc/powerpc)
sys/powerpc/{e500, others} - specific to e500 or other specs to be supported

The problem with current PowerPC port however is OF dependencies, so to 
have really clean separation for potential further platforms support the 
current port should be also split into strict AIM part (which would be 
used by all AIM ports) and strict OF part.

What is your view and recommended route to follow? Can we work together 
on redisigning the sys/powerpc layout to make it more extensible when 
new platforms are added etc.?

I believe FreeBSD/ARM folks must have had similar considerations 
exercise as they have a number of different variations within ARM 
family, maybe we can learn from them somehow?

kind regards,
Rafal