[PATCH v2] ARM: let CPUs not being able to run in ARM mode enter in THUMB mode

[Nicolas Pitre]

On Mon, 14 Jan 2013, Uwe Kleine-König 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.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>

Acked-by: Nicolas Pitre <nico at linaro.org>


> ---
> Changes since (implicit) v1,
> id: 1357904397-8476-1-git-send-email-u.kleine-koenig at pengutronix.de:
> 
>  - drop modification to entry for MMU machines
>  - don't select user-visible symbols
>  - rename THUMBONLY_CPU to CPU_THUMBONLY
>  - move CPU_THUMBONLY definition further down in arch/arm/mm/Kconfig
> 
>  arch/arm/Kconfig             |    3 ++-
>  arch/arm/kernel/head-nommu.S |    8 +++++++-
>  arch/arm/mm/Kconfig          |    9 ++++++++-
>  3 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 67874b8..e04c779 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1656,8 +1656,9 @@ config HZ
>  	default 100
>  
>  config THUMB2_KERNEL
> -	bool "Compile the kernel in Thumb-2 mode"
> +	bool "Compile the kernel in Thumb-2 mode" if !CPU_THUMBONLY
>  	depends on CPU_V7 && !CPU_V6 && !CPU_V6K
> +	default y if CPU_THUMBONLY
>  	select AEABI
>  	select ARM_ASM_UNIFIED
>  	select ARM_UNWIND
> diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
> index 3782320..e8ecae2 100644
> --- a/arch/arm/kernel/head-nommu.S
> +++ b/arch/arm/kernel/head-nommu.S
> @@ -32,15 +32,21 @@
>   * numbers for r1.
>   *
>   */
> -	.arm
>  
>  	__HEAD
> +
> +#ifdef CONFIG_CPU_THUMBONLY
> +	.thumb
> +ENTRY(stext)
> +#else
> +	.arm
>  ENTRY(stext)
>  
>   THUMB(	adr	r9, BSYM(1f)	)	@ Kernel is always entered in ARM.
>   THUMB(	bx	r9		)	@ If this is a Thumb-2 kernel,
>   THUMB(	.thumb			)	@ switch to Thumb now.
>   THUMB(1:			)
> +#endif
>  
>  	setmode	PSR_F_BIT | PSR_I_BIT | SVC_MODE, r9 @ ensure svc mode
>  						@ and irqs disabled
> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
> index 3fd629d..8defd63 100644
> --- a/arch/arm/mm/Kconfig
> +++ b/arch/arm/mm/Kconfig
> @@ -397,6 +397,13 @@ config CPU_V7
>  	select CPU_PABRT_V7
>  	select CPU_TLB_V7 if MMU
>  
> +config CPU_THUMBONLY
> +	bool
> +	# There are no CPUs available with MMU that don't implement an ARM ISA:
> +	depends on !MMU
> +	help
> +	  Select this if your CPU doesn't support the 32 bit ARM instructions.
> +
>  # Figure out what processor architecture version we should be using.
>  # This defines the compiler instruction set which depends on the machine type.
>  config CPU_32v3
> @@ -608,7 +615,7 @@ config ARCH_DMA_ADDR_T_64BIT
>  	bool
>  
>  config ARM_THUMB
> -	bool "Support Thumb user binaries"
> +	bool "Support Thumb user binaries" if !CPU_THUMBONLY
>  	depends on CPU_ARM720T || CPU_ARM740T || CPU_ARM920T || CPU_ARM922T || CPU_ARM925T || CPU_ARM926T || CPU_ARM940T || CPU_ARM946E || CPU_ARM1020 || CPU_ARM1020E || CPU_ARM1022 || CPU_ARM1026 || CPU_XSCALE || CPU_XSC3 || CPU_MOHAWK || CPU_V6 || CPU_V6K || CPU_V7 || CPU_FEROCEON
>  	default y
>  	help
> -- 
> 1.7.10.4
>