Unverified Commit 4e4101cf authored by Palmer Dabbelt's avatar Palmer Dabbelt
Browse files

riscv: Add support to no-FPU systems 



This patchset adds an option, CONFIG_FPU, to enable/disable floating-
point support within the kernel.  The kernel's new behavior will be as
follows:

* with CONFIG_FPU=y
  All FPU codes are reserved.  If no FPU is found during booting, a
  global flag will be set, and those functions will be bypassed with
  condition check to that flag.

* with CONFIG_FPU=n
  No floating-point instructions in kernel and all related settings
  are excluded.

Signed-off-by: default avatarPalmer Dabbelt <palmer@sifive.com>
parents aef53f97 9411ec60

arch/riscv/Kconfig

+9 −0
Original line number Diff line number Diff line
@@ -210,6 +210,15 @@ config RISCV_BASE_PMU 


endmenu



config FPU

	bool "FPU support"

	default y

	help

	  Say N here if you want to disable all floating-point related procedure

	  in the kernel.



	  If you don't know what to do here, say Y.



endmenu



menu "Kernel features"

arch/riscv/Makefile

+8 −11
Original line number Diff line number Diff line
@@ -26,7 +26,6 @@ ifeq ($(CONFIG_ARCH_RV64I),y) 
	KBUILD_CFLAGS += -mabi=lp64

	KBUILD_AFLAGS += -mabi=lp64



	KBUILD_MARCH = rv64im

	KBUILD_LDFLAGS += -melf64lriscv

else

	BITS := 32
@@ -34,22 +33,20 @@ else 


	KBUILD_CFLAGS += -mabi=ilp32

	KBUILD_AFLAGS += -mabi=ilp32

	KBUILD_MARCH = rv32im

	KBUILD_LDFLAGS += -melf32lriscv

endif



KBUILD_CFLAGS += -Wall



ifeq ($(CONFIG_RISCV_ISA_A),y)

	KBUILD_ARCH_A = a

endif

ifeq ($(CONFIG_RISCV_ISA_C),y)

	KBUILD_ARCH_C = c

endif



KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)

# ISA string setting

riscv-march-$(CONFIG_ARCH_RV32I)	:= rv32im

riscv-march-$(CONFIG_ARCH_RV64I)	:= rv64im

riscv-march-$(CONFIG_RISCV_ISA_A)	:= $(riscv-march-y)a

riscv-march-$(CONFIG_FPU)		:= $(riscv-march-y)fd

riscv-march-$(CONFIG_RISCV_ISA_C)	:= $(riscv-march-y)c

KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))

KBUILD_AFLAGS += -march=$(riscv-march-y)



KBUILD_CFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)$(KBUILD_ARCH_C)

KBUILD_CFLAGS += -mno-save-restore

KBUILD_CFLAGS += -DCONFIG_PAGE_OFFSET=$(CONFIG_PAGE_OFFSET)

arch/riscv/include/asm/switch_to.h

+11 −1
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
#include <asm/ptrace.h>

#include <asm/csr.h>



#ifdef CONFIG_FPU

extern void __fstate_save(struct task_struct *save_to);

extern void __fstate_restore(struct task_struct *restore_from);
@@ -55,6 +56,14 @@ static inline void __switch_to_aux(struct task_struct *prev, 
	fstate_restore(next, task_pt_regs(next));

}



extern bool has_fpu;

#else

#define has_fpu false

#define fstate_save(task, regs) do { } while (0)

#define fstate_restore(task, regs) do { } while (0)

#define __switch_to_aux(__prev, __next) do { } while (0)

#endif



extern struct task_struct *__switch_to(struct task_struct *,

				       struct task_struct *);
@@ -62,6 +71,7 @@ extern struct task_struct *__switch_to(struct task_struct *, 
do {							\

	struct task_struct *__prev = (prev);		\

	struct task_struct *__next = (next);		\

	if (has_fpu)					\

		__switch_to_aux(__prev, __next);	\

	((last) = __switch_to(__prev, __next));		\

} while (0)

arch/riscv/kernel/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ obj-y += vdso/ 


CFLAGS_setup.o := -mcmodel=medany



obj-$(CONFIG_FPU)		+= fpu.o

obj-$(CONFIG_SMP)		+= smpboot.o

obj-$(CONFIG_SMP)		+= smp.o

obj-$(CONFIG_MODULES)		+= module.o

arch/riscv/kernel/cpufeature.c

+8 −0
Original line number Diff line number Diff line
@@ -22,6 +22,9 @@ 
#include <asm/hwcap.h>



unsigned long elf_hwcap __read_mostly;

#ifdef CONFIG_FPU

bool has_fpu __read_mostly;

#endif



void riscv_fill_hwcap(void)

{
@@ -65,4 +68,9 @@ void riscv_fill_hwcap(void) 
	}



	pr_info("elf_hwcap is 0x%lx", elf_hwcap);



#ifdef CONFIG_FPU

	if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))

		has_fpu = true;

#endif

}

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