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 <[email protected]>

1 files changed, 9 insertions, 5 deletions

diff --git a/arch/openrisc/kernel/traps.c b/arch/openrisc/kernel/traps.c
index 57e0d674eb04..c195be9cc9fc 100644
--- a/arch/openrisc/kernel/traps.c
+++ b/arch/openrisc/kernel/traps.c
@@ -31,6 +31,7 @@
 #include <linux/uaccess.h>
 
 #include <asm/bug.h>
+#include <asm/fpu.h>
 #include <asm/io.h>
 #include <asm/processor.h>
 #include <asm/unwinder.h>
@@ -84,9 +85,8 @@ void show_registers(struct pt_regs *regs)
 		in_kernel = 0;
 
 	pr_info("CPU #: %d\n"
-		"   PC: %08lx    SR: %08lx    SP: %08lx FPCSR: %08lx\n",
-		smp_processor_id(), regs->pc, regs->sr, regs->sp,
-		regs->fpcsr);
+		"   PC: %08lx    SR: %08lx    SP: %08lx\n",
+		smp_processor_id(), regs->pc, regs->sr, regs->sp);
 	pr_info("GPR00: %08lx GPR01: %08lx GPR02: %08lx GPR03: %08lx\n",
 		0L, regs->gpr[1], regs->gpr[2], regs->gpr[3]);
 	pr_info("GPR04: %08lx GPR05: %08lx GPR06: %08lx GPR07: %08lx\n",
@@ -183,7 +183,10 @@ asmlinkage void do_fpe_trap(struct pt_regs *regs, unsigned long address)
 	if (user_mode(regs)) {
 		int code = FPE_FLTUNK;
 #ifdef CONFIG_FPU
-		unsigned long fpcsr = regs->fpcsr;
+		unsigned long fpcsr;
+
+		save_fpu(current);
+		fpcsr = current->thread.fpcsr;
 
 		if (fpcsr & SPR_FPCSR_IVF)
 			code = FPE_FLTINV;
@@ -197,7 +200,8 @@ asmlinkage void do_fpe_trap(struct pt_regs *regs, unsigned long address)
 			code = FPE_FLTRES;
 
 		/* Clear all flags */
-		regs->fpcsr &= ~SPR_FPCSR_ALLF;
+		current->thread.fpcsr &= ~SPR_FPCSR_ALLF;
+		restore_fpu(current);
 #endif
 		force_sig_fault(SIGFPE, code, (void __user *)regs->pc);
 	} else {