Re: [PATCH v2] ARM: new platform for Energy Micro's EFM32 Cortex-M3 SoCs

[Jonathan Austin <jonathan.austin-5wv7dgnIgG8@public.gmane.org>]

On 28/09/13 20:15, Uwe Kleine-König wrote:
> Hi Arnd,
>
> On Fri, Sep 27, 2013 at 11:44:01PM +0200, Arnd Bergmann wrote:
>> On Thursday 26 September 2013, Uwe Kleine-König wrote:
[...]
>> * An ARMv7-M kernel cannot run on either ARMv4/v5 nor ARMv6/v7-A, right?

> The entry convention is different (ARMv7-M doesn't support the ARM
> instruction set but you need to jump into the kernel in ARM mode for
> v4-v7). Other that that I don't know if there is a problem. Maybe
> Jonathan can say anything here?

There's a more fundamental difference between V7M and other things 
before it - V7M uses a different exception model (We don't have the idea 
of SVC, USR, IRQ, FIQ etc, instead it is Thread/Process/Handler modes).

So no, V7M is V7M, I'm afraid.

> Or alternatively if you want an efm32
> devboard, just tell me.

They're cool, I can recommend one ;)

>
>> Do you prevent building such a kernel in Kconfig?
> I'm sure my Kconfig magic isn't waterproof. It took me a few tries to
> expand the multiarch architecture selection to make v7-m selectable at
> all.

There's a patch series I posted in the past for !MMU with Vexpress that 
was a way to have a !MMU without changing the ARCH_MULTIPLATFORM 
configuration:

http://lists.infradead.org/pipermail/linux-arm-kernel/2013-May/168106.html

You could take a look at that as an alternative approach, but the other 
series you've sent looks reasonable from a !MMU/Multiplatform point of 
view, I'm just not sure about the XIP stuff.

Jonny



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