[Buildroot] [git commit branch/next] arch/arm: add option for FPv4 FPU

[Buildroot] [git commit branch/next] arch/arm: add option for FPv4 FPU

[Thomas Petazzoni]

commit: https://git.buildroot.net/buildroot/commit/?id=09c6e28233230a84932591699d802b1b6677f7cf
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/next

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>
---
 arch/Config.in.arm | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/Config.in.arm b/arch/Config.in.arm
index c2f3f8d9a3..e6950cccca 100644
--- 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