MIPS: Loongson: Fix COP2 usage for preemptible kernel

In preemptible kernel, only TIF_USEDFPU flag is reliable to distinguish
whether _init_fpu()/_restore_fp() is needed. Because the value of the
CP0_Status.CU1 isn't changed during preemption.

V2: Fix coding style.
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/7515/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/loongson/loongson-3/cop2-ex.c

@@ -22,13 +22,13 @@
 static int loongson_cu2_call(struct notifier_block *nfb, unsigned long action,
 	void *data)
 {
-	int fpu_enabled;
+	int fpu_owned;
 	int fr = !test_thread_flag(TIF_32BIT_FPREGS);
 
 	switch (action) {
 	case CU2_EXCEPTION:
 		preempt_disable();
-		fpu_enabled = read_c0_status() & ST0_CU1;
+		fpu_owned = __is_fpu_owner();
 		if (!fr)
 			set_c0_status(ST0_CU1 | ST0_CU2);
 		else
@@ -39,8 +39,8 @@ static int loongson_cu2_call(struct notifier_block *nfb, unsigned long action,
 			KSTK_STATUS(current) |= ST0_FR;
 		else
 			KSTK_STATUS(current) &= ~ST0_FR;
-		/* If FPU is enabled, we needn't init or restore fp */
-		if(!fpu_enabled) {
+		/* If FPU is owned, we needn't init or restore fp */
+		if (!fpu_owned) {
 			set_thread_flag(TIF_USEDFPU);
 			if (!used_math()) {
 				_init_fpu();