MPC7455

[Paul White <pwhite@bivio.net>]

Hello!

I've read through the archives of the linuxppc-dev and linuxppc-embedded
mailing lists, and didn't see very much information regarding Linux on
the Motorolai MPC 7455.

I've checked the latest base kernel from kernel.org, 2.4.18, and there
is no 7455 support. I've already done the code to bring Linux up on the
7455, adding it to arch/ppc/kernel/cputable.c, as well as writing a new
setup_cpu_7455, and a new setup_7455_regs function which sets up the
HID0, HID1, and MSSCR0 registers. I am wondering if anyone is interested
in these changes.

In one of the e-mails in the archives, it was suggested to have Linux
configure the 7455 just the same as the 7450, however this will not
work properly.  HID0 has changed quite a bit, as well as HID1, thus
requiring a new setup routine.  It looks as though the 7451 and 7455
are very similar, and the same init code and restrictions apply, however
between the 7450 and 7451, things have changed quite a bit.

If there is no support out there as of yet, I can create a patch file
and send it off, if anyone is interested.

One thing we ran into regarding the MPC7455, however, is that
it does not guarentee Stores before Loads, meaning if you have
code that has:

Load Instruction
Load Instruction
 - This is OK, they will happen in order as long as its Guarded

Store Instruction
Store Instruction
 - This is OK, they will happen in order as long as its Guarded

Load Instruction
Store Instruction
 - This is OK, they will happen in order as long as its Guarded

Store Instruction
Load Instruction
 - This is not guarenteed in order, even if its Guarded

We had to add an eieio to all of our drivers, such as our PCI
driver, which requires a write to one register before reading another.
The eieio must go between the store and the load.

Just a heads up, if no one has tried the 7455 yet!  Let me know
if anyone is interested in the 7455 changes I've done.

Paul White
Senior Engineer, Software
Bivio Networks, Inc.

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