[OpenPower-Firmware] Hardware documentation

[Marty E. Plummer]

On Fri, Oct 11, 2019 at 12:34:52PM -0500, Daniel M Crowell wrote:
> 
> 
> Hopefully you've already perused the documents out here -
> https://www-355.ibm.com/systems/power/openpower/ .  The "Power9 Processor
> Registers" spec at
Yeah, I've browsed it a bit. Its how I ended up figuring out that they
are not simple 'devmem $addr' addresses to read like on simpler(?) chips
like the various arm ones. To be quite fair the entire architechture of
the power9 chips is fascinating, if a bit confusing (for now; I think
I'm slowly learning to grok it)
> https://ibm.ent.box.com/s/ddcdl3g0otdzyiajhkfe3jjh2oy5p3mt has all of the
> scom registers.  From there you can at least decode the registers that
> we're touching in the code.
> 
Yeah. It would be nice if there was some chart indexed by address
instead of alphabetically by name (granted within this index there are
large groups in such an order, but overall its a bit mixed up).
> --
> Dan Crowell
> Senior Software Engineer - Power Systems Enablement Firmware
> IBM Rochester: t/l 553-2987
> dcrowell at us.ibm.com
> 
> __________________
> 
> 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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> 
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