openrisc: Move FPU state out of pt_regs

My original, naive, FPU support patch had the FPCSR register stored
during both the *mode switch* and *context switch*.  This is wasteful.

Also, the original patches did not save the FPU state when handling
signals during the system call fast path.

We fix this by moving the FPCSR state to thread_struct in task_struct.
We also introduce new helper functions save_fpu and restore_fpu which
can be used to sync the FPU with thread_struct.  These functions are now
called when needed:

 - Setting up and restoring sigcontext when handling signals
 - Before and after __switch_to during context switches
 - When handling FPU exceptions
 - When reading and writing FPU register sets

In the future we can further optimize this by doing lazy FPU save and
restore.  For example, FPU sync is not needed when switching to and from
kernel threads (x86 does this).  FPU save and restore does not need to
be done two times if we have both rescheduling and signal work to do.
However, since OpenRISC FPU state is a single register, I leave these
optimizations for future consideration.

Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 3 insertions, 9 deletions

diff --git a/arch/openrisc/kernel/ptrace.c b/arch/openrisc/kernel/ptrace.c
index cf410193095f..5091b18eab4c 100644
--- a/arch/openrisc/kernel/ptrace.c
+++ b/arch/openrisc/kernel/ptrace.c
@@ -98,9 +98,7 @@ static int fpregs_get(struct task_struct *target,
 		       const struct user_regset *regset,
 		       struct membuf to)
 {
-	const struct pt_regs *regs = task_pt_regs(target);
-
-	return membuf_store(&to, regs->fpcsr);
+	return membuf_store(&to, target->thread.fpcsr);
 }
 
 static int fpregs_set(struct task_struct *target,
@@ -108,13 +106,9 @@ static int fpregs_set(struct task_struct *target,
 		       unsigned int pos, unsigned int count,
 		       const void *kbuf, const void __user *ubuf)
 {
-	struct pt_regs *regs = task_pt_regs(target);
-	int ret;
-
 	/* FPCSR */
-	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
-				 &regs->fpcsr, 0, 4);
-	return ret;
+	return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
+				  &target->thread.fpcsr, 0, 4);
 }
 #endif