[PATCH v2 03/19] ARM: rework ARM11 CPU selection logic
Aaro Koskinen
aaro.koskinen at iki.fi
Thu Jul 2 09:14:51 PDT 2026
On Wed, Jul 01, 2026 at 11:23:37PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd at 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 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 at linaro.org>
> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: Aaro Koskinen <aaro.koskinen at iki.fi> # OMAP
> ---
> 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
>
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