[PATCH v2] riscv: Add support to no-FPU systems

From: Alan Kao
Date: Wed Jun 27 2018 - 00:22:44 EST

This patch adds an option, CONFIG_FPU, to enable/disable floating
procedures. Also, some style issues are fixed.

Signed-off-by: Alan Kao <alankao@xxxxxxxxxxxxx>
Cc: Greentime Hu <greentime@xxxxxxxxxxxxx>
Cc: Zong Li <zong@xxxxxxxxxxxxx>
---
arch/riscv/Kconfig | 9 ++++
arch/riscv/Makefile | 19 +++----
arch/riscv/include/asm/switch_to.h | 6 +++
arch/riscv/kernel/entry.S | 3 +-
arch/riscv/kernel/process.c | 7 ++-
arch/riscv/kernel/signal.c | 82 +++++++++++++++++++++---------
6 files changed, 90 insertions(+), 36 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 6debcc4afc72..6069597ba73f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -232,6 +232,15 @@ 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 6d4a5f6c3f4f..ad3033739430 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -26,7 +26,6 @@ ifeq ($(CONFIG_ARCH_RV64I),y)

KBUILD_CFLAGS += -mabi=lp64
KBUILD_AFLAGS += -mabi=lp64
- KBUILD_MARCH = rv64im
LDFLAGS += -melf64lriscv
else
BITS := 32
@@ -34,22 +33,20 @@ else

KBUILD_CFLAGS += -mabi=ilp32
KBUILD_AFLAGS += -mabi=ilp32
- KBUILD_MARCH = rv32im
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) := $(riscv-march-y)c
+KBUILD_CFLAGS += -march=$(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)

diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index dd6b05bff75b..de333c012227 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 +55,11 @@ static inline void __switch_to_aux(struct task_struct *prev,
fstate_save(prev, regs);
fstate_restore(next, task_pt_regs(next));
}
+#else
+#define fstate_save(task, regs) do { } while (0)
+#define fstate_restore(task, regs) do { } while (0)
+#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..99d20283bb62 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -83,7 +83,12 @@ 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;
+ /* User mode, irqs on */
+#ifdef CONFIG_FPU
+ regs->sstatus = SR_SPIE | SR_FS_INITIAL;
+#else
+ regs->sstatus = SR_SPIE | SR_FS_OFF;
+#endif
regs->sepc = pc;
regs->sp = sp;
set_fs(USER_DS);
diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 718d0c984ef0..a7a5ed5598a8 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -37,8 +37,9 @@ struct rt_sigframe {
struct ucontext uc;
};

-static long restore_d_state(struct pt_regs *regs,
- struct __riscv_d_ext_state __user *state)
+#ifdef CONFIG_FPU
+static inline long __restore_d_state(struct pt_regs *regs,
+ struct __riscv_d_ext_state __user *state)
{
long err;
err = __copy_from_user(&current->thread.fstate, state, sizeof(*state));
@@ -47,35 +48,75 @@ static long restore_d_state(struct pt_regs *regs,
return err;
}

-static long save_d_state(struct pt_regs *regs,
- struct __riscv_d_ext_state __user *state)
+static inline long __save_d_state(struct pt_regs *regs,
+ struct __riscv_d_ext_state __user *state)
{
fstate_save(current, regs);
return __copy_to_user(state, &current->thread.fstate, sizeof(*state));
}

-static long restore_sigcontext(struct pt_regs *regs,
- struct sigcontext __user *sc)
+static long restore_d_state(struct pt_regs *regs,
+ union __riscv_fp_state *sc_fpregs)
{
long err;
size_t i;
- /* sc_regs is structured the same as the start of pt_regs */
- err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
- if (unlikely(err))
- return err;
+
/* Restore the floating-point state. */
- err = restore_d_state(regs, &sc->sc_fpregs.d);
+ err = __restore_d_state(regs, &sc_fpregs->d);
if (unlikely(err))
return err;
/* We support no other extension state at this time. */
- for (i = 0; i < ARRAY_SIZE(sc->sc_fpregs.q.reserved); i++) {
+ for (i = 0; i < ARRAY_SIZE(sc_fpregs->q.reserved); i++) {
u32 value;
- err = __get_user(value, &sc->sc_fpregs.q.reserved[i]);
+ err = __get_user(value, &sc_fpregs->q.reserved[i]);
if (unlikely(err))
break;
if (value != 0)
return -EINVAL;
}
+
+ return 0;
+}
+
+static long save_d_state(struct pt_regs *regs,
+ union __riscv_fp_state *sc_fpregs)
+{
+ long err;
+ size_t i;
+
+ /* Save the floating-point state. */
+ err = __save_d_state(regs, &sc_fpregs->d);
+ /* We support no other extension state at this time. */
+ for (i = 0; i < ARRAY_SIZE(sc_fpregs->q.reserved); i++)
+ err |= __put_user(0, &sc_fpregs->q.reserved[i]);
+
+ return err;
+}
+#else
+static long restore_d_state(struct pt_regs *regs,
+ union __riscv_fp_state *sc_fpregs)
+{
+ return 0;
+}
+
+static long save_d_state(struct pt_regs *regs,
+ union __riscv_fp_state *sc_fpregs)
+{
+ return 0;
+}
+#endif
+
+static long restore_sigcontext(struct pt_regs *regs,
+ struct sigcontext __user *sc)
+{
+ long err;
+ /* sc_regs is structured the same as the start of pt_regs */
+ err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
+ if (unlikely(err))
+ return err;
+ /* Restore the floating-point state. */
+ err = restore_d_state(regs, &sc->sc_fpregs);
+
return err;
}

@@ -120,23 +161,18 @@ SYSCALL_DEFINE0(rt_sigreturn)
}

static long setup_sigcontext(struct rt_sigframe __user *frame,
- struct pt_regs *regs)
+ struct pt_regs *regs)
{
struct sigcontext __user *sc = &frame->uc.uc_mcontext;
long err;
- 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));
- /* 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]);
+ err |= save_d_state(regs, &sc->sc_fpregs);
return err;
}

static inline void __user *get_sigframe(struct ksignal *ksig,
- struct pt_regs *regs, size_t framesize)
+ struct pt_regs *regs, size_t framesize)
{
unsigned long sp;
/* Default to using normal stack */
@@ -160,7 +196,7 @@ static inline void __user *get_sigframe(struct ksignal *ksig,


static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
- struct pt_regs *regs)
+ struct pt_regs *regs)
{
struct rt_sigframe __user *frame;
long err = 0;
@@ -279,7 +315,7 @@ static void do_signal(struct pt_regs *regs)
* - triggered by the _TIF_WORK_MASK flags
*/
asmlinkage void do_notify_resume(struct pt_regs *regs,
- unsigned long thread_info_flags)
+ unsigned long thread_info_flags)
{
/* Handle pending signal delivery */
if (thread_info_flags & _TIF_SIGPENDING)
--
2.18.0