powerpc: Make flush_fp_to_thread() nop when CONFIG_PPC_FPU is disabled

In the current kernel, the function flush_fp_to_thread() is not
dependent on CONFIG_PPC_FPU. So most invocations of this function
is not wrapped by CONFIG_PPC_FPU. Even through we don't really
save the FPRs to the thread struct if CONFIG_PPC_FPU is not enabled,
but there does have some runtime overhead such as the check for
tsk->thread.regs and preempt disable and enable. It really make
no sense to do that. So make it a nop when CONFIG_PPC_FPU is
disabled. Also remove the wrapped #ifdef CONFIG_PPC_FPU
when invoking this function.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index 33e1cd823585..39cf0f6cc373 100644
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -19,7 +19,6 @@ extern struct task_struct *_switch(struct thread_struct *prev,
 extern void giveup_fpu(struct task_struct *);
 extern void load_up_fpu(void);
 extern void enable_kernel_fp(void);
-extern void flush_fp_to_thread(struct task_struct *);
 extern void enable_kernel_altivec(void);
 extern void load_up_altivec(struct task_struct *);
 extern int emulate_altivec(struct pt_regs *);
@@ -37,6 +36,12 @@ static inline void discard_lazy_cpu_state(void)
 }
 #endif
 
+#ifdef CONFIG_PPC_FPU
+extern void flush_fp_to_thread(struct task_struct *);
+#else
+static inline void flush_fp_to_thread(struct task_struct *t) { }
+#endif
+
 #ifdef CONFIG_ALTIVEC
 extern void flush_altivec_to_thread(struct task_struct *);
 extern void giveup_altivec(struct task_struct *);