From: jonathan.austin@arm•com (Jonathan Austin)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] ARM: let CPUs not being able to run in ARM mode enter in THUMB mode
Date: Fri, 11 Jan 2013 15:34:39 +0000 [thread overview]
Message-ID: <50F0310F.3070502@arm.com> (raw)
In-Reply-To: <1357904397-8476-1-git-send-email-u.kleine-koenig@pengutronix.de>
Hi Uwe,
On 11/01/13 11:39, Uwe Kleine-K?nig wrote:
> Some ARM cores are not capable to run in ARM mode (e.g. Cortex-M3). So
> obviously these cannot enter the kernel in ARM mode. Make an exception
> for them and let them enter in THUMB mode.
Clearly something like this is necessary, but it isn't something I'd
like for people to start using *unless* they have a THUMB only CPU (for
example, to work around dodgy boot-loaders, etc)
Seeing as there are no THUMB-only CPUs with an MMU, I think we could
safely constrain this change to:
a) depend on !MMU
b) only touch head-nommu.S
Does that cause any issue for what you're doing.
[...]
> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
> index 3fd629d..bc3150c 100644
> --- a/arch/arm/mm/Kconfig
> +++ b/arch/arm/mm/Kconfig
> @@ -1,5 +1,11 @@
> comment "Processor Type"
>
> +# Select this if your CPU doesn't support the 32 bit ARM instructions.
> +config THUMBONLY_CPU
> + bool
> + select THUMB2_KERNEL
> + select ARM_THUMB
> +
> # Select CPU types depending on the architecture selected. This selects
> # which CPUs we support in the kernel image, and the compiler instruction
> # optimiser behaviour.
Also, a couple of minor questions about this:
- What's the rationale for the placement within the file - it looks a
bit curious up the top there.
- Given the fact that we don't want people using this except in very
specific circumstances, should we write a little bit of help for the option?
Jonny
next prev parent reply other threads:[~2013-01-11 15:34 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-11 11:39 [PATCH] ARM: let CPUs not being able to run in ARM mode enter in THUMB mode Uwe Kleine-König
2013-01-11 15:34 ` Jonathan Austin [this message]
2013-01-11 15:51 ` Uwe Kleine-König
2013-01-12 17:19 ` Nicolas Pitre
2013-01-11 16:07 ` Russell King - ARM Linux
2013-01-11 16:20 ` Uwe Kleine-König
2013-01-14 9:50 ` Uwe Kleine-König
2013-01-11 18:00 ` Jonathan Austin
2013-01-11 18:12 ` Russell King - ARM Linux
2013-01-14 11:15 ` [PATCH v2] " Uwe Kleine-König
2013-01-14 21:53 ` Nicolas Pitre
2013-01-29 12:44 ` [PATCH] " Dave Martin
2013-01-31 15:51 ` Uwe Kleine-König
2013-02-19 11:39 ` Dave Martin
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