ARM: mpu: Allow enabling of the MPU via kconfig

Allows the user to select MPU support when compiling for ARM processors
that support the PMSAv7.

This ensures that CONFIG_SMP depends on the MPU in the case that no MMU
is present.

CONFIG_SMP_ON_UP is not implemented for nommu, so introduce an MMU
dependency there.

Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>

2 files changed, 13 insertions, 2 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5543d36c2834..ec38cacb3d08 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1414,7 +1414,7 @@ config SMP
         depends on CPU_V6K || CPU_V7
         depends on GENERIC_CLOCKEVENTS
         depends on HAVE_SMP
-        depends on MMU
+        depends on MMU || ARM_MPU
         select USE_GENERIC_SMP_HELPERS
         help
           This enables support for systems with more than one CPU. If you have
@@ -1435,7 +1435,7 @@ config SMP
 
 config SMP_ON_UP
         bool "Allow booting SMP kernel on uniprocessor systems (EXPERIMENTAL)"
-        depends on SMP && !XIP_KERNEL
+        depends on SMP && !XIP_KERNEL && MMU
         default y
         help
           SMP kernels contain instructions which fail on non-SMP processors.
diff --git a/arch/arm/Kconfig-nommu b/arch/arm/Kconfig-nommu
index c859495da480..db597e1c7572 100644
--- a/arch/arm/Kconfig-nommu
+++ b/arch/arm/Kconfig-nommu
@@ -50,3 +50,14 @@ config REMAP_VECTORS_TO_RAM
           Otherwise, say 'y' here.  In this case, the kernel will require
           external support to redirect the hardware exception vectors to
           the writable versions located at DRAM_BASE.
+
+config ARM_MPU
+       bool 'Use the ARM v7 PMSA Compliant MPU'
+       default y
+       help
+         Some ARM systems without an MMU have instead a Memory Protection
+         Unit (MPU) that defines the type and permissions for regions of
+         memory.
+
+         If your CPU has an MPU then you should choose 'y' here unless you
+         know that you do not want to use the MPU.