Re: Building for MMU-less vexpress targets

Commit Message

Jonathan Austin Jan. 8, 2013, 7:01 p.m. UTC

Nicolas,

On 06/11/12 23:14, Nicolas Pitre wrote:
> On Tue, 6 Nov 2012, Arnd Bergmann wrote:
>
>> On Tuesday 06 November 2012, Nicolas Pitre wrote:
>
>> The two options are either to make
>> vexpress be single-platform when building for !MMU, or to allow multiplatform
>> kernels to be built without MMU support in principle. I think the second
>> option is more logical and avoids complex Kconfig constructs.
>
> Well, I'd rather prefer to think that the first option is the most
> logical between those 2 options, regardless of Kconfig complexity
> issues.
>
> I didn't look, but just making MULTIPLATFORM depend on !MMU, and
> VEXPRESS depend on MULTIPLATFORM || MMU should be close to what is
> needed, no?
>

I've spent a little bit of time trying this, as both Arnd and you seemed 
to be happy with a solution along these lines.

However, I can't seem to make it fall out quite so trivially so I wonder 
if you'd mind clarifying what you were expecting:

The problem that I see when I try to do this is that ARCH_VEXPRESS no 
longer exists in the 'choice' for "ARM system type" in arch/arm/Kconfig. 
A solution that allows selection of VEXPRESS as a single platform (!MMU) 
and multi-platform (MMU) appears to need an entry in that 'choice' for 
the single platform case, and a config option in 
arch/arm/mach-vexpress/Kconfig for the multiplatform one.

So it seems to me we need a shim in one of those two locations...

As Will suggested a while back, the shim in arch/arm/Kconfig could look 
like:

---8<---
---->8----

With the other perhaps being to merge the ARCH_VEXPRESS option back in 
to the 'choice' and create a ARCH_VEXPRESS_MULTI elsewhere...

Is that the sort of thing you had in mind, or is there another way 
around that I'm missing?

Thanks,

Jonny

Comments

Arnd Bergmann Jan. 8, 2013, 7:11 p.m. UTC | #1

On Tuesday 08 January 2013, Jonathan Austin wrote:
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 335e220..0561d87 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -305,6 +305,11 @@ config ARCH_REALVIEW
>          help
>            This enables support for ARM Ltd RealView boards.
> 
> +config ARCH_VEXPRESS_NOMMU
> +       bool "ARM Ltd. Versatile Express family (nommu)"
> +       depends on !MMU
> +       select ARCH_VEXPRESS
> +
>   config ARCH_VERSATILE
>          bool "ARM Ltd. Versatile family"
>          select ARCH_WANT_OPTIONAL_GPIOLIB
> ---->8----

Yes, I think this is the right approach.

> With the other perhaps being to merge the ARCH_VEXPRESS option back in 
> to the 'choice' and create a ARCH_VEXPRESS_MULTI elsewhere...

That would needlessly break 'make oldconfig' for people that have
CONFIG_ARCH_VEXPRESS in their .config files or other scripts.

> Is that the sort of thing you had in mind, or is there another way 
> around that I'm missing?

I think it's good.

Acked-by: Arnd Bergmann <[e-mail]>

Nicolas Pitre Jan. 8, 2013, 7:22 p.m. UTC | #2

On Tue, 8 Jan 2013, Arnd Bergmann wrote:

> On Tuesday 08 January 2013, Jonathan Austin wrote:
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index 335e220..0561d87 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -305,6 +305,11 @@ config ARCH_REALVIEW
> >          help
> >            This enables support for ARM Ltd RealView boards.
> > 
> > +config ARCH_VEXPRESS_NOMMU
> > +       bool "ARM Ltd. Versatile Express family (nommu)"
> > +       depends on !MMU
> > +       select ARCH_VEXPRESS
> > +
> >   config ARCH_VERSATILE
> >          bool "ARM Ltd. Versatile family"
> >          select ARCH_WANT_OPTIONAL_GPIOLIB
> > ---->8----
> 
> Yes, I think this is the right approach.
> 
> > With the other perhaps being to merge the ARCH_VEXPRESS option back in 
> > to the 'choice' and create a ARCH_VEXPRESS_MULTI elsewhere...
> 
> That would needlessly break 'make oldconfig' for people that have
> CONFIG_ARCH_VEXPRESS in their .config files or other scripts.
> 
> > Is that the sort of thing you had in mind, or is there another way 
> > around that I'm missing?
> 
> I think it's good.
> 
> Acked-by: Arnd Bergmann <[e-mail]>

Looks fine to me too.  Perhaps the vexpress option would logically fit 
better if located after versatile instead of being in the middle of 
realview and versatile.

Other than that:

Acked-by: Nicolas Pitre <[e-mail]>


Nicolas

Patch

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 335e220..0561d87 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -305,6 +305,11 @@  config ARCH_REALVIEW
         help
           This enables support for ARM Ltd RealView boards.

+config ARCH_VEXPRESS_NOMMU
+       bool "ARM Ltd. Versatile Express family (nommu)"
+       depends on !MMU
+       select ARCH_VEXPRESS
+
  config ARCH_VERSATILE
         bool "ARM Ltd. Versatile family"
         select ARCH_WANT_OPTIONAL_GPIOLIB