6 files changed, 29 insertions, 3 deletions

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index a344980287a5..a63f9dbb4706 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -208,6 +208,15 @@ 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 type"
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 01393e1b2921..901770fc9bd2 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -44,7 +44,7 @@ KBUILD_CFLAGS += -Wall
 riscv-march-$(CONFIG_ARCH_RV32I)        := rv32im
 riscv-march-$(CONFIG_ARCH_RV64I)        := rv64im
 riscv-march-$(CONFIG_RISCV_ISA_A)       := $(riscv-march-y)a
-riscv-march-y                           := $(riscv-march-y)fd
+riscv-march-$(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)
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index dd6b05bff75b..093050b03543 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -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 +56,15 @@ static inline void __switch_to_aux(struct task_struct *prev,
         fstate_restore(next, task_pt_regs(next));
 }
 
+#define DEFAULT_SSTATUS (SR_SPIE | SR_FS_INITIAL)
+
+#else
+#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)
+#define DEFAULT_SSTATUS (SR_SPIE | SR_FS_OFF)
+#endif
+
 extern struct task_struct *__switch_to(struct task_struct *,
                                        struct task_struct *);
 
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index bd433efd915e..f13f7f276639 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -13,7 +13,6 @@ extra-y += vmlinux.lds
 obj-y   += cpu.o
 obj-y   += cpufeature.o
 obj-y   += entry.o
-obj-y   += fpu.o
 obj-y   += irq.o
 obj-y   += process.o
 obj-y   += ptrace.o
@@ -32,6 +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
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index d7c6ca7c95ae..07d515655aa9 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -76,7 +76,7 @@ void show_regs(struct pt_regs *regs)
 void start_thread(struct pt_regs *regs, unsigned long pc,
         unsigned long sp)
 {
-        regs->sstatus = SR_SPIE /* User mode, irqs on */ | SR_FS_INITIAL;
+        regs->sstatus = DEFAULT_SSTATUS;
         regs->sepc = pc;
         regs->sp = sp;
         set_fs(USER_DS);
@@ -84,12 +84,14 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 
 void flush_thread(void)
 {
+#ifdef CONFIG_FPU
         /*
          * Reset FPU context
          *      frm: round to nearest, ties to even (IEEE default)
          *      fflags: accrued exceptions cleared
          */
         memset(&current->thread.fstate, 0, sizeof(current->thread.fstate));
+#endif
 }
 
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 6a18b9819ead..2450b824d799 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -37,6 +37,7 @@ struct rt_sigframe {
         struct ucontext uc;
 };
 
+#ifdef CONFIG_FPU
 static long restore_fp_state(struct pt_regs *regs,
                              union __riscv_fp_state *sc_fpregs)
 {
@@ -85,6 +86,10 @@ static long save_fp_state(struct pt_regs *regs,
 
         return err;
 }
+#else
+#define save_fp_state(task, regs) (0)
+#define restore_fp_state(task, regs) (0)
+#endif
 
 static long restore_sigcontext(struct pt_regs *regs,
         struct sigcontext __user *sc)