Re: [PATCH v2 03/19] ARM: rework ARM11 CPU selection logic

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

On 01/07/2026 23:23:37+0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Support for SMP on ARM1136r0 has been broken for a while, and nobody
> is working on fixing it. I had a plan to change ARMv6 support to no
> longer coexist in a common kernel with ARMv7 CPUs but instead ARMv5 and
> below. This would have addressed the problem, but after a recent mailing
> list discussion, we concluded that an easier approach is to just forbid
> ARM1136r0 CPU support on SMP-enabled kernels.
> 
> This mainly affects users of the Nokia N800/N810 tablets using an
> OMAP2420 SoC, which is the only commercial product with an ARM1136r0
> that is still supported by the kernel.
> 
> The other machines that are still in the same hardware catogory are:
> 
>  - TI OMAP2420 H4 reference board
>  - TI OMAP2430 SDP software development platform
>  - Freescale/NXP i.MX31 Lite Development Kit
>  - Buglabs i.MX31 Bug 1.x prototype
>  - Arm Integrator/AP with CM1136JF-S core module
> 
> To my knowledge, none of these have any actual users aside from
> reference boards being used more easily test the platforms.

There is a missing "to" in this sentence ;)

> 
> There are also a few ARM1136r1 machines, which implement the
> ARMv6K SMP support (barriers, atomics and TLS):
> 
>  - Eukrea CPUIMX35 reference platform
>  - Freescale/NXP i.MX35 Product Development Kit
>  - ARM Integrator/CP/IM-LT3 with ARM1136J Core Tile
>  - ARM Realview/EB with ARM1136J Core Tile
> 
> Again, these are mainly reference implementations rather than
> actual products, but since they support ARMv6K, they should
> continue to work correctly in SMP-enabled kernels. For the
> ARM Core Tile, I have not found a datasheet but instead use
> the revision based on what the respective virtual models
> report.
> 
> All the other ARMv6 platforms use an ARM1176 with ARMv6K,
> VMSAv7 and Trustzone support.
> 
> To avoid the broken configuration, annotate the ARM1136 based
> machines with specific CPU_ARM1136R0 or CPU_ARM1136R2 symbols
> in Kconfig and make the r0 variants depend on !SMP.
> 
> Link: https://lore.kernel.org/linux-arm-kernel/2831c5a6-cfbf-4fe0-b51c-0396e5b0aeb7@app.fastmail.com/T/
> Acked-by: Linus Walleij <linus.walleij@linaro.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  arch/arm/Kconfig.platforms      |  2 +-
>  arch/arm/mach-imx/Kconfig       |  4 +++-
>  arch/arm/mach-omap2/Kconfig     |  3 ++-
>  arch/arm/mach-versatile/Kconfig | 10 +++++-----
>  arch/arm/mm/Kconfig             | 24 +++++++++++++++++++++++-
>  5 files changed, 34 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm/Kconfig.platforms b/arch/arm/Kconfig.platforms
> index 386eccc81868..2e118b65f93b 100644
> --- a/arch/arm/Kconfig.platforms
> +++ b/arch/arm/Kconfig.platforms
> @@ -33,7 +33,7 @@ config ARCH_MULTI_V4_V5
>  config ARCH_MULTI_V6
>  	bool "ARMv6 based platforms (ARM11)"
>  	select ARCH_MULTI_V6_V7
> -	select CPU_V6K
> +	select CPU_ARM1176
>  
>  config ARCH_MULTI_V7
>  	bool "ARMv7 based platforms (Cortex-A, PJ4, Scorpion, Krait)"
> diff --git a/arch/arm/mach-imx/Kconfig b/arch/arm/mach-imx/Kconfig
> index a361840d7a04..041e73ad203a 100644
> --- a/arch/arm/mach-imx/Kconfig
> +++ b/arch/arm/mach-imx/Kconfig
> @@ -41,13 +41,15 @@ comment "ARM1136 platforms"
>  
>  config SOC_IMX31
>  	bool "i.MX31 support"
> -	select CPU_V6
> +	depends on !SMP
> +	select CPU_ARM1136R0
>  	select MXC_AVIC
>  	help
>  	  This enables support for Freescale i.MX31 processor
>  
>  config SOC_IMX35
>  	bool "i.MX35 support"
> +	select CPU_ARM1136R1
>  	select MXC_AVIC
>  	help
>  	  This enables support for Freescale i.MX35 processor
> diff --git a/arch/arm/mach-omap2/Kconfig b/arch/arm/mach-omap2/Kconfig
> index f3f19bcfca2c..13987ffbba00 100644
> --- a/arch/arm/mach-omap2/Kconfig
> +++ b/arch/arm/mach-omap2/Kconfig
> @@ -8,8 +8,9 @@ config OMAP_HWMOD
>  config ARCH_OMAP2
>  	bool "TI OMAP2"
>  	depends on ARCH_MULTI_V6
> +	depends on !SMP
>  	select ARCH_OMAP2PLUS
> -	select CPU_V6
> +	select CPU_ARM1136R0
>  	select OMAP_HWMOD
>  	select SOC_HAS_OMAP2_SDRC
>  
> diff --git a/arch/arm/mach-versatile/Kconfig b/arch/arm/mach-versatile/Kconfig
> index 513618078440..de42da7de8c8 100644
> --- a/arch/arm/mach-versatile/Kconfig
> +++ b/arch/arm/mach-versatile/Kconfig
> @@ -113,7 +113,8 @@ config INTEGRATOR_CM1136JFS
>  	bool "Integrator/CM1136JF-S core module"
>  	depends on ARCH_INTEGRATOR_AP
>  	depends on ARCH_MULTI_V6
> -	select CPU_V6
> +	depends on !SMP
> +	select CPU_ARM1136R0
>  
>  config ARCH_INTEGRATOR_CP
>  	bool "Support Integrator/CP platform"
> @@ -135,7 +136,7 @@ config INTEGRATOR_CTB36
>  	bool "Integrator/CTB36 (ARM1136JF-S) core tile"
>  	depends on ARCH_INTEGRATOR_CP
>  	depends on ARCH_MULTI_V6
> -	select CPU_V6
> +	select CPU_ARM1136R1
>  
>  config ARCH_CINTEGRATOR
>  	depends on ARCH_INTEGRATOR_CP
> @@ -182,7 +183,7 @@ config MACH_REALVIEW_EB
>  config REALVIEW_EB_ARM1136
>  	bool "Support ARM1136J(F)-S Tile"
>  	depends on MACH_REALVIEW_EB && ARCH_MULTI_V6
> -	select CPU_V6
> +	select CPU_ARM1136R1
>  	help
>  	  Enable support for the ARM1136 tile fitted to the
>  	  Realview(R) Emulation Baseboard platform.
> @@ -201,11 +202,10 @@ config REALVIEW_EB_A9MP
>  	  Enable support for the Cortex-A9MPCore tile fitted to the
>  	  Realview(R) Emulation Baseboard platform.
>  
> -# ARMv6 CPU without K extensions, but does have the new exclusive ops
>  config MACH_REALVIEW_PB1176
>  	bool "Support RealView(R) Platform Baseboard for ARM1176JZF-S"
>  	depends on ARCH_MULTI_V6
> -	select CPU_V6
> +	select CPU_ARM1176
>  	select HAVE_TCM
>  	help
>  	  Include support for the ARM(R) RealView(R) Platform Baseboard for
> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
> index 871bd58d2ccc..f3d71e89a31f 100644
> --- a/arch/arm/mm/Kconfig
> +++ b/arch/arm/mm/Kconfig
> @@ -376,6 +376,7 @@ config CPU_PJ4B
>  # ARMv6
>  config CPU_V6
>  	bool
> +	depends on !SMP
>  	select CPU_32v6
>  	select CPU_ABRT_EV6
>  	select CPU_CACHE_V6
> @@ -386,7 +387,6 @@ config CPU_V6
>  	select CPU_PABRT_V6
>  	select CPU_THUMB_CAPABLE
>  	select CPU_TLB_V6 if MMU
> -	select SMP_ON_UP if SMP
>  
>  # ARMv6k
>  config CPU_V6K
> @@ -403,6 +403,28 @@ config CPU_V6K
>  	select CPU_THUMB_CAPABLE
>  	select CPU_TLB_V6 if MMU
>  
> +config CPU_ARM1136R0
> +	bool
> +	select CPU_V6
> +	depends on !SMP
> +	help
> +	  These early revisions of ARM1136 lack support for the
> +	  ARMv6k extensions for multiprocessing.
> +
> +config CPU_ARM1136R1
> +	bool
> +	select CPU_V6K
> +	help
> +	  Later revisions of ARM1136 add ARMv6k (atomics, barriers
> +	  and TLS register) in addition to the features from r0.
> +
> +config CPU_ARM1176
> +	bool
> +	select CPU_V6K
> +	help
> +	  ARM1176 implements ARMv6k, VMSAv7 and Trustzone in
> +	  addition to the ARMv6 baseline.
> +
>  # ARMv7 and ARMv8 architectures
>  config CPU_V7
>  	bool
> -- 
> 2.39.5
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com