arch/ppc/kernel clutter

[Paul Mackerras]

I feel that arch/ppc/kernel in the linuxppc_2_4_devel tree is getting
more than a bit cluttered.  I propose that we make a new
arch/ppc/platforms directory and move the platform-specific files into
there - i.e. all of *_setup.c, *_pic.c, *_pci.c, and maybe some
others.  What would be left in arch/ppc/kernel is the more generic
stuff, i.e. things relating to the different base processors, the
different types of interrupt controllers or PCI host bridges, the
generic stuff that interfaces to the rest of the kernel (e.g. setup.c)
and so on.

My idea is that adding support for a new board would not normally
require changes in arch/ppc/kernel unless the new board has a new type
of interrupt controller, PCI host bridge, etc.

Thoughts?  Objections?

Another thing I would like to do is to generalize the drivers for the
various on-chip peripherals a bit more.  The platform code would then
specify in some way "this platform has an XYZZY on-chip ethernet
controller with registers at 0xabcdef00, using interrupt 123, with
quirks A, D and F".  (This sort of thing is what the OF device tree
was designed for and does very well, BTW.)

The configuration scripts could force CONFIG_XYZZY on when this
platform is selected and that would compile in the xyzzy driver.
The xyzzy driver initialization would get called during boot and would
look up whether the platform has any XYZZY's, and if so, what
addresses and interrupts to use.  So the XYZZY code doesn't need to
know anything about which platforms have an XYZZY at all.

This would be a bit of work in the short term to implement but would
mean that we could potentially reuse code more easily for new
platforms.  The idea is that if a new platform has an XYZZY, the
platform setup code just has to create a device tree (or whatever)
node for it, make sure the XYZZY driver is configured in, and it
should (hopefully :) Just Work.

This could extend to things like interrupt controllers and PCI host
bridges as well as regular I/O devices, too.

Paul.

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