linux-kernel - Re: [PATCH v4 07/11] ARM: allow MULTIPLATFORM with !MMU

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Date:	Sun, 5 Apr 2015 17:10:14 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Stefan Agner <stefan@...er.ch>
Cc:	shawn.guo@...aro.org, kernel@...gutronix.de,
	u.kleine-koenig@...gutronix.de, jason@...edaemon.net,
	olof@...om.net, arnd@...db.de, daniel.lezcano@...aro.org,
	tglx@...utronix.de, mark.rutland@....com, pawel.moll@....com,
	robh+dt@...nel.org, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, marc.zyngier@....com,
	mcoquelin.stm32@...il.com, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 07/11] ARM: allow MULTIPLATFORM with !MMU

On Sat, Apr 04, 2015 at 01:56:20AM +0200, Stefan Agner wrote:
> On 2015-04-03 22:09, Russell King - ARM Linux wrote:
> > On Fri, Apr 03, 2015 at 09:44:48PM +0200, Stefan Agner wrote:
> >> In order to support SoC with heterogenous CPU architectures (such
> >> as Freescale Vybrid/i.MXSX) it is preferable to use the same
> >> architecture (ARCH_MXC in this case) for the MMU enabled and !MMU
> >> CPU. Hence allow to select MULTIPLATFORM even without MMU.
> >>
> >> Signed-off-by: Stefan Agner <stefan@...er.ch>
> >> ---
> >>  arch/arm/Kconfig | 21 ++++++++++-----------
> >>  1 file changed, 10 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> >> index 9f1f09a..636cb3f 100644
> >> --- a/arch/arm/Kconfig
> >> +++ b/arch/arm/Kconfig
> >> @@ -230,7 +230,7 @@ config VECTORS_BASE
> >>  	  in size.
> >>
> >>  config ARM_PATCH_PHYS_VIRT
> >> -	bool "Patch physical to virtual translations at runtime" if EMBEDDED
> >> +	bool "Patch physical to virtual translations at runtime" if EMBEDDED || (ARCH_MULTIPLATFORM && MMU)
> >>  	default y
> > 
> > This makes no sense.  Multiplatform MMU _requires_ this feature, so why
> > offer it to the user when multiplatform is enabled _and_ MMU is enabled?
> 
> I see, this is plain wrong. Will replace that with a select ... if MMU
> in multiplatform.

I think what I'd like to see is, in the top level choice:

config ARM_SINGLE_ARMV7M
	bool "ARM architecture v7M compliant (Cortex-M0/M3/M4) SoC"
	depends on !MMU
	select ARM_NVIC
	... etc ...

which then allows a /multiplatform/ v7M kernel to be built, allowing the
selection of EFM32, SOC_VF610, and any other v7M compliant SoC.

So, it's very similar to multiplatform in the sense that several SoCs
can be built together, but we preserve the need not to build
incompatible stuff together.

Thoughts?

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