[OpenPower-Firmware] Hardware documentation

[Daniel M Crowell]

I definitely feel your pain on the documentation front.  There are a few
reasons why these sorts of things don't currently exist.  Obviously there
is the usual "developers don't like to write docs" excuse :-).  The next
reason is that a lot of this stuff crosses the open/proprietary line.  The
internal hardware specifications are still full of proprietary IP, but the
code is open.  There hasn't been a concerted effort (that I know of) to
create completely open hardware specifications because frankly there hasn't
been a lot of interest to this point in anyone external playing around with
this stuff.   You are blazing a trail here.

There are some specifications out in the OpenPOWER organization.  For
example, OpenFSI is here -
http://openpowerfoundation.org/wp-content/uploads/resources/OpenFSI-spec-100/content/ch01.html
  (pretty low-level electrical stuff though)

We've tried to provide a lot of comments where we can but as with all
long-term projects, there is a lot of inertia-based code.  The Hostboot FSI
code is based on the behavior of FSP code from 3 generations ago since the
hardware logic is essentially unchanged.  So at the moment the code is the
documentation, for all that is worth.  If you point us at some specific
chunk of logic that is too opaque we can try to beef it up with comments.

--
Dan Crowell
Senior Software Engineer - Power Systems Enablement Firmware
IBM Rochester: t/l 553-2987
dcrowell at us.ibm.com



From:	"Marty E. Plummer" <hanetzer at startmail.com>
To:	openpower-firmware at lists.ozlabs.org
Date:	10/10/2019 04:40 AM
Subject:	[EXTERNAL] [OpenPower-Firmware] Hardware documentation
Sent by:	"OpenPower-Firmware" <openpower-firmware-bounces
            +dcrowell=us.ibm.com at lists.ozlabs.org>



Hello all.

So, I've gotten to the point I believe I've got code execution working
(at the very least in theory; still need to do *something* easily
detectable like writing a string to the scratch register) and am
investigating what happens during the following isteps. I'm having a
hard time following the execution of the c++ code past kernel.C due to
all the indirections, and was wondering if there was some form of docs
one could use as a reference.

Consider the arm pl011 uart driver, for example; it has a broad overview
of the registers and their functionality specific to that particular
piece of IP. Are there similar documents for fsi/scom/xscom/etc for the
power9 chips? I already have register documents 1-3 for the p9 but they
strike me as too broad, covering almost every thing in what seem to be
very ... unspecific(?) ways. Something like 'to initialize the fsi bus,
write 0xdeadbeef to register 0xdeadcode; to read something write this to
there' and so on.

Thanks,
Marty
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