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Subject[PATCH v5 4/5] Allow to disable FPU support
Date
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 <alankao@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Cc: Vincent Chen <vincentc@andestech.com>
Cc: Zong Li <zong@andestech.com>
Cc: Nick Hu <nickhu@andestech.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
arch/riscv/Kconfig | 9 +++++++++
arch/riscv/include/asm/switch_to.h | 10 ++++++++++
arch/riscv/kernel/Makefile | 2 +-
arch/riscv/kernel/process.c | 4 +++-
arch/riscv/kernel/signal.c | 5 +++++
5 files changed, 28 insertions(+), 2 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/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 cb209139ba53..3820d89e2db9 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -83,7 +83,7 @@ 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);
@@ -91,12 +91,14 @@ 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)
--
2.18.0
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