Allow to disable FPU support

NonerKao · palmer-dabbelt · commit 9671f7061433 · 2018-10-22T17:02:23.000-07:00
FPU codes have been separated from common part in previous patches.
This patch add the CONFIG_FPU option and some stubs, so that a no-FPU
configuration is allowed.

Signed-off-by: Alan Kao &lt;alankao@andestech.com&gt;
Cc: Greentime Hu &lt;greentime@andestech.com&gt;
Cc: Vincent Chen &lt;vincentc@andestech.com&gt;
Cc: Zong Li &lt;zong@andestech.com&gt;
Cc: Nick Hu &lt;nickhu@andestech.com&gt;
Reviewed-by: Christoph Hellwig &lt;hch@lst.de&gt;
Signed-off-by: Palmer Dabbelt &lt;palmer@sifive.com&gt;
diff --git 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
@@ -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
@@ -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
@@ -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
@@ -76,20 +76,22 @@ 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);
 }
 
 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
@@ -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)

Original file line number	Diff line number	Diff line change
`@@ -76,20 +76,22 @@ void show_regs(struct pt_regs *regs)`
`76`	`76`	`void start_thread(struct pt_regs *regs, unsigned long pc,`
`77`	`77`	`unsigned long sp)`
`78`	`78`	`{`
`79`		`- regs->sstatus = SR_SPIE /* User mode, irqs on */ \| SR_FS_INITIAL;`
	`79`	`+ regs->sstatus = DEFAULT_SSTATUS;`
`80`	`80`	`regs->sepc = pc;`
`81`	`81`	`regs->sp = sp;`
`82`	`82`	`set_fs(USER_DS);`
`83`	`83`	`}`
`84`	`84`
`85`	`85`	`void flush_thread(void)`
`86`	`86`	`{`
	`87`	`+#ifdef CONFIG_FPU`
`87`	`88`	`/*`
`88`	`89`	`* Reset FPU context`
`89`	`90`	`* frm: round to nearest, ties to even (IEEE default)`
`90`	`91`	`* fflags: accrued exceptions cleared`
`91`	`92`	`*/`
`92`	`93`	`memset(&current->thread.fstate, 0, sizeof(current->thread.fstate));`
	`94`	`+#endif`
`93`	`95`	`}`
`94`	`96`
`95`	`97`	`int arch_dup_task_struct(struct task_struct dst, struct task_struct src)`