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Kconfig: clean up FPU and FPU_SHARING entries

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CONFIG_FPU: The architecture dependency list is redundant.
Having CPU_HAS_FPU being selected by those archs as a dependency
is sufficient and cleaner.

CONFIG_FPU_SHARING: The default should always be y to be on the safe
side here, but as a compromise for not affecting existing config, let's
move the default selection local to those configs that care, again to
avoid a growing list of conditionals here. Adjust the help text which
applies to more than just Cortex-M.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2021-04-07 21:41:06 -04:00 • committed by Carles Cufí
commit 949ef7c660
2 changed files with 9 additions and 10 deletions
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18
arch/Kconfig
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@ -830,7 +830,6 @@ menu "Floating Point Options"
config FPU
bool "Enable floating point unit (FPU)"
depends on CPU_HAS_FPU
depends on ARC || ARM || RISCV || SPARC || X86
help
This option enables the hardware Floating Point Unit (FPU), in order to
support using the floating point registers and instructions.
@ -851,20 +850,19 @@ config FPU
config FPU_SHARING
bool "FPU register sharing"
depends on FPU && MULTITHREADING
default y if ARM && ARMV7_M_ARMV8_M_FP
help
This option enables preservation of the hardware floating point registers
across context switches to allow multiple threads to perform concurrent
floating point operations.
Note that on Cortex-M processors with the floating point extension we
enable by default the FPU register sharing mode, as some GCC compilers
may activate a floating point context by generating FP instructions for
any thread, and that context must be preserved when switching such
threads in and out. The developers can still disable the FP sharing
mode in their application projects, and switch to Unshared FP registers
mode, if it is guaranteed that the image code does not generate FP
instructions outside the single thread context that is allowed to do so.
Note that some compiler configurations may activate a floating point
context by generating FP instructions for any thread, and that
context must be preserved when switching such threads in and out.
The developers can still disable the FP sharing mode in their
application projects, and switch to Unshared FP registers mode,
if it is guaranteed that the image code does not generate FP
instructions outside the single thread context that is allowed
to do so.
endmenu

1
arch/arm/core/aarch32/cortex_m/Kconfig
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@ -244,6 +244,7 @@ config ARMV8_M_SE
config ARMV7_M_ARMV8_M_FP
bool
depends on ARMV7_M_ARMV8_M_MAINLINE && !CPU_CORTEX_M3
imply FPU_SHARING
help
This option signifies the use of an ARMv7-M processor
implementation, or the use of an ARMv8-M processor