[PATCH] riscv: Add support to no-FPU systems

[PATCH] riscv: Add support to no-FPU systems

[Alan Kao]

This patch adds an option, CONFIG_FPU, so that we can enable/disable
floating procedures in kernel.

Signed-off-by: Alan Kao <alankao@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Cc: Zong Li <zong@andestech.com>
---
 arch/riscv/Kconfig                 | 4 ++++
 arch/riscv/Makefile                | 4 ++++
 arch/riscv/include/asm/switch_to.h | 4 ++++
 arch/riscv/kernel/entry.S          | 3 ++-
 arch/riscv/kernel/process.c        | 6 ++++++
 arch/riscv/kernel/signal.c         | 6 ++++++
 6 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 6debcc4afc72..429d0bf777c9 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -232,6 +232,10 @@ config RISCV_BASE_PMU
 
 endmenu
 
+config FPU
+	bool "FPU support"
+	default y
+
 endmenu
 
 menu "Kernel type"
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 76e958a5414a..2719e768c4dc 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -47,7 +47,11 @@ ifeq ($(CONFIG_RISCV_ISA_C),y)
 	KBUILD_ARCH_C = c
 endif
 
+ifeq ($(CONFIG_FPU),y)
 KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
+else
+KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)$(KBUILD_ARCH_C)
+endif
 
 KBUILD_CFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)$(KBUILD_ARCH_C)
 KBUILD_CFLAGS += -mno-save-restore
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index dd6b05bff75b..da0327a74466 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);
 
@@ -54,6 +55,9 @@ static inline void __switch_to_aux(struct task_struct *prev,
 		fstate_save(prev, regs);
 	fstate_restore(next, task_pt_regs(next));
 }
+#else
+#define __switch_to_aux(__prev, __next)
+#endif
 
 extern struct task_struct *__switch_to(struct task_struct *,
 				       struct task_struct *);
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 9aaf6c986771..89867c9aa4f5 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -357,6 +357,7 @@ ENTRY(__switch_to)
 	ret
 ENDPROC(__switch_to)
 
+#ifdef CONFIG_FPU
 ENTRY(__fstate_save)
 	li  a2,  TASK_THREAD_F0
 	add a0, a0, a2
@@ -442,7 +443,7 @@ ENTRY(__fstate_restore)
 	csrc sstatus, t1
 	ret
 ENDPROC(__fstate_restore)
-
+#endif
 
 	.section ".rodata"
 	/* Exception vector table */
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index cb209139ba53..a817046e478a 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -83,7 +83,11 @@ void show_regs(struct pt_regs *regs)
 void start_thread(struct pt_regs *regs, unsigned long pc,
 	unsigned long sp)
 {
+#ifdef CONFIG_FPU
 	regs->sstatus = SR_SPIE /* User mode, irqs on */ | SR_FS_INITIAL;
+#else
+	regs->sstatus = SR_SPIE | SR_FS_OFF;
+#endif
 	regs->sepc = pc;
 	regs->sp = sp;
 	set_fs(USER_DS);
@@ -101,7 +105,9 @@ void flush_thread(void)
 
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
+#ifdef CONFIG_FPU
 	fstate_save(src, task_pt_regs(src));
+#endif
 	*dst = *src;
 	return 0;
 }
diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 718d0c984ef0..0f659c9ef465 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_d_state(struct pt_regs *regs,
 	struct __riscv_d_ext_state __user *state)
 {
@@ -53,6 +54,7 @@ static long save_d_state(struct pt_regs *regs,
 	fstate_save(current, regs);
 	return __copy_to_user(state, &current->thread.fstate, sizeof(*state));
 }
+#endif
 
 static long restore_sigcontext(struct pt_regs *regs,
 	struct sigcontext __user *sc)
@@ -63,6 +65,7 @@ static long restore_sigcontext(struct pt_regs *regs,
 	err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
 	if (unlikely(err))
 		return err;
+#ifdef CONFIG_FPU
 	/* Restore the floating-point state. */
 	err = restore_d_state(regs, &sc->sc_fpregs.d);
 	if (unlikely(err))
@@ -76,6 +79,7 @@ static long restore_sigcontext(struct pt_regs *regs,
 		if (value != 0)
 			return -EINVAL;
 	}
+#endif
 	return err;
 }
 
@@ -127,11 +131,13 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
 	size_t i;
 	/* sc_regs is structured the same as the start of pt_regs */
 	err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
+#ifdef CONFIG_FPU
 	/* Save the floating-point state. */
 	err |= save_d_state(regs, &sc->sc_fpregs.d);
 	/* We support no other extension state at this time. */
 	for (i = 0; i < ARRAY_SIZE(sc->sc_fpregs.q.reserved); i++)
 		err |= __put_user(0, &sc->sc_fpregs.q.reserved[i]);
+#endif
 	return err;
 }
 
-- 
2.17.0

Re: [PATCH] riscv: Add support to no-FPU systems

[Christoph Hellwig]

> +ifeq ($(CONFIG_FPU),y)
>  KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
> +else
> +KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)$(KBUILD_ARCH_C)
> +endif

Can we refactor that KBUILD_ARCH code into something like

riscv-march-y				:=
riscv-march-$(CONFIG_ARCH_RV32I)	+= rv32im
riscv-march-$(CONFIG_ARCH_RV64I)	+= rv64im
riscv-march-$(CONFIG_RISCV_ISA_A)	+= a
riscv-march-$(CONFIG_FPU)		+= fd
riscv-march-$(CONFIG_RISCV_ISA_C)	+= c

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

> +#ifdef CONFIG_FPU
>  	regs->sstatus = SR_SPIE /* User mode, irqs on */ | SR_FS_INITIAL;
> +#else
> +	regs->sstatus = SR_SPIE | SR_FS_OFF;
> +#endif

Having the comment in one branch, but not the other is odd.  I'd be
tempted to just remove t entirely, but if not it should be move up
or duplicated.

>  int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
>  {
> +#ifdef CONFIG_FPU
>  	fstate_save(src, task_pt_regs(src));
> +#endif

Please provide a !CONFIG_FPU stub for fstate_save, please.

>  }
> +#endif
>  
>  static long restore_sigcontext(struct pt_regs *regs,
>  	struct sigcontext __user *sc)
> @@ -63,6 +65,7 @@ static long restore_sigcontext(struct pt_regs *regs,
>  	err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
>  	if (unlikely(err))
>  		return err;
> +#ifdef CONFIG_FPU
>  	/* Restore the floating-point state. */
>  	err = restore_d_state(regs, &sc->sc_fpregs.d);
>  	if (unlikely(err))
> @@ -76,6 +79,7 @@ static long restore_sigcontext(struct pt_regs *regs,
>  		if (value != 0)
>  			return -EINVAL;
>  	}
> +#endif

Same here.

> @@ -127,11 +131,13 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
>  	size_t i;
>  	/* sc_regs is structured the same as the start of pt_regs */
>  	err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
> +#ifdef CONFIG_FPU
>  	/* Save the floating-point state. */
>  	err |= save_d_state(regs, &sc->sc_fpregs.d);
>  	/* We support no other extension state at this time. */
>  	for (i = 0; i < ARRAY_SIZE(sc->sc_fpregs.q.reserved); i++)
>  		err |= __put_user(0, &sc->sc_fpregs.q.reserved[i]);
> +#endif

Same here.

Re: [PATCH] riscv: Add support to no-FPU systems

[Alan Kao]

On Wed, Jun 20, 2018 at 11:39:38PM -0700, Christoph Hellwig wrote:
> > +ifeq ($(CONFIG_FPU),y)
> >  KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
> > +else
> > +KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)$(KBUILD_ARCH_C)
> > +endif
> 
> Can we refactor that KBUILD_ARCH code into something like
> 
> riscv-march-y				:=
> riscv-march-$(CONFIG_ARCH_RV32I)	+= rv32im
> riscv-march-$(CONFIG_ARCH_RV64I)	+= rv64im
> riscv-march-$(CONFIG_RISCV_ISA_A)	+= a
> riscv-march-$(CONFIG_FPU)		+= fd
> riscv-march-$(CONFIG_RISCV_ISA_C)	+= c
> 
> KBUILD_CFLAGS += -march=$(riscv-march-y)
> 

That's neat, sure.

> > +#ifdef CONFIG_FPU
> >  	regs->sstatus = SR_SPIE /* User mode, irqs on */ | SR_FS_INITIAL;
> > +#else
> > +	regs->sstatus = SR_SPIE | SR_FS_OFF;
> > +#endif
> 
> Having the comment in one branch, but not the other is odd.  I'd be
> tempted to just remove t entirely, but if not it should be move up
> or duplicated.
> 

I'll move that comment up.

> >  int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> >  {
> > +#ifdef CONFIG_FPU
> >  	fstate_save(src, task_pt_regs(src));
> > +#endif
> 
> Please provide a !CONFIG_FPU stub for fstate_save, please.
> 
> >  }

It's OK to do this to fstate_save/restore, and

> > +#endif
> >  
> >  static long restore_sigcontext(struct pt_regs *regs,
> >  	struct sigcontext __user *sc)
> > @@ -63,6 +65,7 @@ static long restore_sigcontext(struct pt_regs *regs,
> >  	err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
> >  	if (unlikely(err))
> >  		return err;
> > +#ifdef CONFIG_FPU
> >  	/* Restore the floating-point state. */
> >  	err = restore_d_state(regs, &sc->sc_fpregs.d);
> >  	if (unlikely(err))
> > @@ -76,6 +79,7 @@ static long restore_sigcontext(struct pt_regs *regs,
> >  		if (value != 0)
> >  			return -EINVAL;
> >  	}
> > +#endif
> 
> Same here.
> 

it's also OK to do so to restore_d_state/save_d_state.  But what to do with the
following __get_user/__put_user calls?

Can I rename existing restore_d_state to __restore_d_state, and create a new
function restore_d_state which includes the original restore_d_state/__get_user
pair, and the same to save_d_state?

> > @@ -127,11 +131,13 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
> >  	size_t i;
> >  	/* sc_regs is structured the same as the start of pt_regs */
> >  	err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
> > +#ifdef CONFIG_FPU
> >  	/* Save the floating-point state. */
> >  	err |= save_d_state(regs, &sc->sc_fpregs.d);
> >  	/* We support no other extension state at this time. */
> >  	for (i = 0; i < ARRAY_SIZE(sc->sc_fpregs.q.reserved); i++)
> >  		err |= __put_user(0, &sc->sc_fpregs.q.reserved[i]);
> > +#endif
> 
> Same here.
> 

Thanks,
Alan