linux-kernel - Re: [PATCH v2 4/5] ARM: allow errata and XIP options to be enabled without ARCH_MULTIPLATFORM

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Message-ID: <20141028143118.GH27405@n2100.arm.linux.org.uk>
Date:	Tue, 28 Oct 2014 14:31:18 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Xia Kaixu <kaixu.xia@...aro.org>, arm@...nel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 4/5] ARM: allow errata and XIP options to be enabled
 without ARCH_MULTIPLATFORM_STRICT

On Tue, Oct 28, 2014 at 03:24:38PM +0100, Arnd Bergmann wrote:
> On Tuesday 28 October 2014 14:02:31 Russell King - ARM Linux wrote:
> > On Tue, Oct 28, 2014 at 09:31:34PM +0800, Xia Kaixu wrote:
> > > With the ARCH_MULTIPLATFORM_STRICT option, it becomes much easier to
> > > enable the ERRATA options when we know at configuration time that we
> > > don't care about the generic case. The previous configuration makes
> > > XIP_KERNEL option fundamentally non-MULTIPLATFORM, but it's still
> > > valid to select it when building for !ARCH_MULTIPLATFORM_STRICT and
> > > selecting only the one machine that you want to run on.
> > 
> > XIP_KERNEL isn't supported on anything past ARMv5 though.
> 
> I would really like to get some of the platforms that currently use
> XIP_KERNEL to use ARCH_MULTIPLATFORM in the long run. One of them
> is EFM32, which is ARMv7-M.

Right, and on ARMv7-M, the restrictions against XIP_KERNEL don't apply.
The restrictions on XIP_KERNEL only apply with MMU-full kernels, because
of the remapping needed - the kernel is executed from flash, which is
mapped separately, and that mapping needs to be setup in order to turn
the MMU on.

With ARMv7-M, there is no MMU to worry about, no other mappings are
required, so there is no special platform specific setup applicable.

So, I don't see any reason why XIP_KERNEL can't depend on
!ARCH_MULTIPLATFORM || CPU_V7M.

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