Re: very minor 405GP and 405GPr PCI difference

[David Gibson <david@gibson.dropbear.id.au>]

On Thu, Oct 24, 2002 at 07:50:33PM -0400, Ralph Blach wrote:
> David,
>
> Let me expain
>
> On the 405gp, the PMM0 enable is hardwired 1 and  cannot be overwritten
> by software.   This makes the PMM0 region permantly enabled on the
> 405GP.  I cannot be turned off.

Yes, I realise this.

> When the technology port was done, the design of the PCI was changed
> slightly because the designer made the PMM0 enable bit writable.  It is
> still initalized to a 1, but it can written to a 0.
>
> In the current software, the initialization software writes a 0 to PMM0
> and to PMM1.  This was fine on the 405gp because the enable bit for PMM0
> could not be changed.  On the 405GPr this disabled PMM0 and with PMM1
> disabled, bad things happened.
>
> The initialization software simply need to write a 1 to the PMM0 enable
> bit and all will be well.

Yes, I know that's the problem that triggered this discussion, but
it's only part of what we're covering now.

Since I was looking at the code it seemed like a good idea to try to
consolidate this stuff for the various boards at the same time.
Otherwise we'll have to fix this in the code for every 405GPr board in
the tree, and every 405GP board too or people will copy the broken
code.  Then it will keep coming back as people merge board ports that
haven't caught up with the fix.

I'm trying to find out how the various boards are meaning to set up
the PCI mappings, and come up with the simplest scheme we can to
handle that.  At the moment this code (on most of the boards) is
confused and suggest to me that it was written without really
understanding what was intended and how to go about accomplishing it.

> David Gibson wrote:
> >On Tue, Oct 22, 2002 at 02:55:47PM -0700, Todd Poynor wrote:
> >
> >>David Gibson wrote (regarding Rainier PMM1 bios_fixup in MVL):
> >>
> >>
> >>>Well, it may be in a different place, but it looks like it has the
> >>>same problem.  It is still establishing a PCI window at PLB address
> >>>0x80000000, which is the same address used for the PMM0 window - or is
> >>>that also different in the MV kernel?
> >>>
> >>>I'd be trying to work out what that mapping's actually for, first.  I
> >>>still can't see how it can possibly work - if there are overlapping
> >>>PMM windows, what actually happens to accesses in that (PLB) range?
> >>
> >>Yes, it looks like MVL only sets up the one window using PMM1... we've
> >>started an effort to have the Rainier-knowedgeable folks get the code
> >>sync'ed up with the community and this should happen soon.
> >
> >
> >Hang on, so just to clarify - MVL sets up PMM1 with the code you
> >posted, but doesn't set up PMM0 anywhere?  From my reading of that
> >code, it sets up a window at the same address as the "standard"
> >(Walnut) mapping, except that it is only 128kB instead of 1GB.  Is
> >there a reason that Rainier must have such a small window?
> >
>
>
>

--
David Gibson			| For every complex problem there is a
david@gibson.dropbear.id.au	| solution which is simple, neat and
				| wrong.
http://www.ozlabs.org/people/dgibson

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/