Re: [PATCH] powerpc/powernv: Remove powernv RTAS support

[Michael Ellerman <mpe@ellerman.id.au>]

On Fri, 2015-03-27 at 18:24 +0530, Aneesh Kumar K.V wrote:
> Michael Ellerman <mpe@ellerman.id.au> writes:
> 
> > The powernv code has some conditional support for running on bare metal
> > machines that have no OPAL firmware, but provide RTAS.
> >
> > No released machines ever supported that, and even in the lab it was
> > just a transitional hack in the days when OPAL was still being
> > developed.
> >
> > So remove the code.
> 
> So when we select CONFIG_PPC_PSERIES, we end up selecting
> CONFIG_PPC_RTAS. What is the expected behaviour there for powernv ? 

After this patch, the expected behaviour is that the powernv platform code
won't use RTAS, even if it's there. And that's fine because no real powernv
machines have RTAS.

In a perfect world the RTAS code would be isolated in platforms/pseries, but
it's used on other platforms, so it's a bit messier than that. But the expected
behaviour is that the powernv code won't use RTAS, even if the code is still
built in.

Is that what you meant?

> Can we use RTAS call from powernv code if rtas node is present in device
> tree ? 

Yes you can, if you build with CONFIG_PPC_RTAS=y. Though when I add a
powernv_defconfig (soon), it won't have CONFIG_PPC_RTAS.

> Or do we want to make sure powernv always use OPAL call ?

It depends what you mean by "powernv". Once this patch is applied the powernv
*platform* code will not use RTAS.

There may still be other code that can be built into a kernel and booted on
powernv that then uses RTAS. That's fine, if it makes sense for someone, I
don't think we need to prevent that happening.

> For example, right now we will use rtas_node get-term-char and
> put-term-char even with this patch applied.

Well you will *if* your machine has RTAS, and you have CONFIG_HVC_RTAS=y and/or
CONFIG_UDBG_RTAS_CONSOLE=y.

So I think that's fine?

cheers