32-bit kernel on PPC64 supported?

32-bit kernel on PPC64 supported?

[Marvin]

Hi,

while trying to cleanup some configs/makefiles for ppc64 I noticed, that 
CONFIG_POWER4 implies CONFIG_PPC64 and vice versa in all defconfigs.
So I want to boldly replace CONFIG_POWER4 by CONFIG_PPC64 - ugh.

However, there are some constructs like:

#ifndef CONFIG_PPC64
...
#ifdef CONFIG_POWER4
...
#endif
...
#endif /* CONFIG_PPC64 */

in which POWER4 is always undefined, e.g. in 
include/asm-powerpc/mmu_context.h. Maybe this is a leftover from times, where 
64-bit kernels where not supported on Powermacs. Is this 32-bit support still 
necessary?

Greetings

Marvin

Re: 32-bit kernel on PPC64 supported?

[Arnd Bergmann]

On Friday 18 July 2008, Marvin wrote:
> in which POWER4 is always undefined, e.g. in 
> include/asm-powerpc/mmu_context.h. Maybe this is a leftover from times, where 
> 64-bit kernels where not supported on Powermacs. Is this 32-bit support still 
> necessary?

There is currently no 64-bit machine that is supported by current kernels,
and I don't think there is any reason to add this again.

I'm not sure what the point of your plan to replace CONFIG_POWER4 is, but
it sounds like this case is slightly different, as you remove a potential
feature, so I guess it should be a separate patch.

	Arnd <><

Re: 32-bit kernel on PPC64 supported?

[Benjamin Herrenschmidt]

On Fri, 2008-07-18 at 20:43 +0200, Marvin wrote:
> Hi,
> 
> while trying to cleanup some configs/makefiles for ppc64 I noticed, that 
> CONFIG_POWER4 implies CONFIG_PPC64 and vice versa in all defconfigs.
> So I want to boldly replace CONFIG_POWER4 by CONFIG_PPC64 - ugh.

No, those are different.

CONFIG_PPC64 means a 64 bits kernel.

CONFIG_POWER4 means a 64 bits kernel that only runs on IBM POWER4 and
later (ie, processors conforming to, iirc, version 2.01 or later of
the architecture).

That is, it's legal to have CONFIG_PPC64 and !CONFIG_POWER4, and this
is even necessary if you want to boot on a POWER3 or an RS64 processor.

Now, there also used to be some 32 bits support for POWER4 and G5 but
that has been dropped a while ago.

Cheers,
Ben.

Re: 32-bit kernel on PPC64 supported?

[Marvin]

Hi,

On Saturday 19 July 2008 00:14:35 Benjamin Herrenschmidt wrote:
> On Fri, 2008-07-18 at 20:43 +0200, Marvin wrote:
> > Hi,
> >
> > while trying to cleanup some configs/makefiles for ppc64 I noticed, that
> > CONFIG_POWER4 implies CONFIG_PPC64 and vice versa in all defconfigs.
> > So I want to boldly replace CONFIG_POWER4 by CONFIG_PPC64 - ugh.
>
> No, those are different.
>
> CONFIG_PPC64 means a 64 bits kernel.
>
> CONFIG_POWER4 means a 64 bits kernel that only runs on IBM POWER4 and
> later (ie, processors conforming to, iirc, version 2.01 or later of
> the architecture).
>
> That is, it's legal to have CONFIG_PPC64 and !CONFIG_POWER4, and this
> is even necessary if you want to boot on a POWER3 or an RS64 processor.

I don't want to replace CONFIG_POWER4 by void, but by something like 
CONFIG_TUNE_POWER4 (see my previous post, one week ago). So there is 
no "feature loss". CONFIG_POWER3 is used only to define HAVE_BATS, so I 
thought I can clean this up. 

> Now, there also used to be some 32 bits support for POWER4 and G5 but
> that has been dropped a while ago.

Ok - that's fine. 

I hope to finish my patches during the weekend, so things will become more 
clear. 

Greetings

Marvin