arch/arm: add option for FPv4 FPU

The FPv4-SP FPU is a single-precision FPU with 16 double registers [0]
[1]. It is only available for cortex-m4 cores, and is known to gcc as
fpv4-sp-d16 (note that there is no leading 'v') since gcc-4.5 [2].

[0] https://en.wikipedia.org/wiki/ARM_Cortex-M#Cortex-M4
[1] https://developer.arm.com/docs/ddi0439/latest/floating-point-unit
[2] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=639cb7b789a54bf78d6ae5e2644450f5eb1837a6

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

diff --git a/arch/Config.in.arm b/arch/Config.in.arm
index c2f3f8d9a36f6ecc56d7da3bdcce9937e101daad..e6950cccca37adcee9fff57c6ef2fb80ac62dc50 100644 (file)
--- a/arch/Config.in.arm
+++ b/arch/Config.in.arm
@@ -40,6 +40,15 @@ config BR2_ARM_CPU_HAS_VFPV4
        bool
        select BR2_ARM_CPU_HAS_VFPV3
 
+# FPv4 is always optional
+config BR2_ARM_CPU_MAYBE_HAS_FPV4
+       bool
+       select BR2_ARM_CPU_MAYBE_HAS_FPU
+
+config BR2_ARM_CPU_HAS_FPV4
+       bool
+       select BR2_ARM_CPU_HAS_FPU
+
 config BR2_ARM_CPU_HAS_FP_ARMV8
        bool
        select BR2_ARM_CPU_HAS_VFPV4
@@ -460,6 +469,7 @@ config BR2_ARM_ENABLE_NEON
 config BR2_ARM_ENABLE_VFP
        bool "Enable VFP extension support"
        depends on BR2_ARM_CPU_MAYBE_HAS_FPU
+       select BR2_ARM_CPU_HAS_FPV4 if BR2_ARM_CPU_MAYBE_HAS_FPV4
        select BR2_ARM_CPU_HAS_VFPV4 if BR2_ARM_CPU_MAYBE_HAS_VFPV4
        select BR2_ARM_CPU_HAS_VFPV3 if BR2_ARM_CPU_MAYBE_HAS_VFPV3
        select BR2_ARM_CPU_HAS_VFPV2 if BR2_ARM_CPU_MAYBE_HAS_VFPV2
@@ -526,6 +536,7 @@ endchoice
 choice
        prompt "Floating point strategy"
        default BR2_ARM_FPU_FP_ARMV8 if BR2_ARM_CPU_HAS_FP_ARMV8
+       default BR2_ARM_FPU_FPV4D16 if BR2_ARM_CPU_HAS_FPV4
        default BR2_ARM_FPU_VFPV4D16 if BR2_ARM_CPU_HAS_VFPV4
        default BR2_ARM_FPU_VFPV3D16 if BR2_ARM_CPU_HAS_VFPV3
        default BR2_ARM_FPU_VFPV2 if BR2_ARM_CPU_HAS_VFPV2
@@ -636,6 +647,14 @@ config BR2_ARM_FPU_NEON_VFPV4
          example on Cortex-A5 and Cortex-A7, support for VFPv4 and
          NEON is optional.
 
+config BR2_ARM_FPU_FPV4D16
+       bool "FPv4-D16"
+       depends on BR2_ARM_CPU_HAS_FPV4
+       help
+         This option allows to use the FPv4-SP (single precision)
+         floating point unit, as available in some ARMv7m processors
+         (Cortex-M4).
+
 config BR2_ARM_FPU_FP_ARMV8
        bool "FP-ARMv8"
        depends on BR2_ARM_CPU_HAS_FP_ARMV8
@@ -768,6 +787,7 @@ config BR2_GCC_TARGET_FPU
        default "vfpv4-d16"     if BR2_ARM_FPU_VFPV4D16
        default "neon"          if BR2_ARM_FPU_NEON
        default "neon-vfpv4"    if BR2_ARM_FPU_NEON_VFPV4
+       default "fpv4-sp-d16"   if BR2_ARM_FPU_FPV4D16
        default "fp-armv8"      if BR2_ARM_FPU_FP_ARMV8
        default "neon-fp-armv8" if BR2_ARM_FPU_NEON_FP_ARMV8
        depends on BR2_arm || BR2_armeb