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

On Fri, 2015-03-27 at 18:24 +0530, Aneesh Kumar K.V wrote:

Michael Ellerman [off-list ref] writes:

quoted

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