MIPS: Loongson-3: Enable the COP2 usage

Loongson-3 has some specific instructions (MMI/SIMD) in coprocessor 2.
COP2 isn't independent because it share COP1 (FPU)'s registers. This
patch enable the COP2 usage so user-space programs can use the MMI/SIMD
instructions. When COP2 exception happens, we enable both COP1 (FPU)
and COP2, only in this way the fp context can be saved and restored
correctly.

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/7189/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/cop2.h

@@ -32,6 +32,14 @@ extern void nlm_cop2_restore(struct nlm_cop2_state *);
 #define cop2_present		1
 #define cop2_lazy_restore	0
 
+#elif defined(CONFIG_CPU_LOONGSON3)
+
+#define cop2_save(r)
+#define cop2_restore(r)
+
+#define cop2_present		1
+#define cop2_lazy_restore	1
+
 #else
 
 #define cop2_present		0

arch/mips/loongson/loongson-3/Makefile

@@ -1,7 +1,7 @@
 #
 # Makefile for Loongson-3 family machines
 #
-obj-y			+= irq.o
+obj-y			+= irq.o cop2-ex.o
 
 obj-$(CONFIG_SMP)	+= smp.o
 

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

@@ -0,0 +1,63 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2014 Lemote Corporation.
+ *   written by Huacai Chen <chenhc@lemote.com>
+ *
+ * based on arch/mips/cavium-octeon/cpu.c
+ * Copyright (C) 2009 Wind River Systems,
+ *   written by Ralf Baechle <ralf@linux-mips.org>
+ */
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/notifier.h>
+
+#include <asm/fpu.h>
+#include <asm/cop2.h>
+#include <asm/current.h>
+#include <asm/mipsregs.h>
+
+static int loongson_cu2_call(struct notifier_block *nfb, unsigned long action,
+	void *data)
+{
+	int fpu_enabled;
+	int fr = !test_thread_flag(TIF_32BIT_FPREGS);
+
+	switch (action) {
+	case CU2_EXCEPTION:
+		preempt_disable();
+		fpu_enabled = read_c0_status() & ST0_CU1;
+		if (!fr)
+			set_c0_status(ST0_CU1 | ST0_CU2);
+		else
+			set_c0_status(ST0_CU1 | ST0_CU2 | ST0_FR);
+		enable_fpu_hazard();
+		KSTK_STATUS(current) |= (ST0_CU1 | ST0_CU2);
+		if (fr)
+			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) {
+			set_thread_flag(TIF_USEDFPU);
+			if (!used_math()) {
+				_init_fpu();
+				set_used_math();
+			} else
+				_restore_fp(current);
+		}
+		preempt_enable();
+
+		return NOTIFY_STOP;	/* Don't call default notifier */
+	}
+
+	return NOTIFY_OK;		/* Let default notifier send signals */
+}
+
+static int __init loongson_cu2_setup(void)
+{
+	return cu2_notifier(loongson_cu2_call, 0);
+}
+early_initcall(loongson_cu2_setup);