MIPS: kernel: mips-r2-to-r6-emul: Add R2 emulator for MIPS R6

MIPS R6 removed quite a few R2 instructions. However, there
is plenty of <R6 userland code so we add an in-kernel emulator
so we can still be able to execute all R2 userland out there.

The emulator comes with a handy debugfs under /mips/ directory
(r2-emul-stats) to provide some basic statistics of the
instructions that are being emulated.

Below are some statistics from booting a minimal buildroot image:

Instruction     Total   BDslot
------------------------------
movs            236969  0
hilo            56686   0
muls            55279   0
divs            10941   0
dsps            0       0
bops            1       0
traps           0       0
fpus            0       0
loads           214981  17
stores          103364  0
llsc            56898   0
dsemul          150418  0
jr              370158
bltzl           43
bgezl           1594
bltzll          0
bgezll          0
bltzal          39
bgezal          39
beql            14503
bnel            138741
blezl           0
bgtzl           3988

Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>

2 files changed, 96 insertions, 3 deletions

diff --git a/arch/mips/include/asm/branch.h b/arch/mips/include/asm/branch.h
index 2894ea58454..de781cf54bc 100644
--- a/arch/mips/include/asm/branch.h
+++ b/arch/mips/include/asm/branch.h
@@ -13,9 +13,6 @@
 #include <asm/ptrace.h>
 #include <asm/inst.h>
 
-static int mipsr2_emulation = 0;
-#define NO_R6EMU	(cpu_has_mips_r6 && !mipsr2_emulation)
-
 extern int __isa_exception_epc(struct pt_regs *regs);
 extern int __compute_return_epc(struct pt_regs *regs);
 extern int __compute_return_epc_for_insn(struct pt_regs *regs,
diff --git a/arch/mips/include/asm/mips-r2-to-r6-emul.h b/arch/mips/include/asm/mips-r2-to-r6-emul.h
new file mode 100644
index 00000000000..60570f2c3ba
--- /dev/null
+++ b/arch/mips/include/asm/mips-r2-to-r6-emul.h
@@ -0,0 +1,96 @@
+/*
+ * 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 Imagination Technologies Ltd.
+ * Author: Markos Chandras <markos.chandras@imgtec.com>
+ */
+
+#ifndef __ASM_MIPS_R2_TO_R6_EMUL_H
+#define __ASM_MIPS_R2_TO_R6_EMUL_H
+
+struct mips_r2_emulator_stats {
+	u64 movs;
+	u64 hilo;
+	u64 muls;
+	u64 divs;
+	u64 dsps;
+	u64 bops;
+	u64 traps;
+	u64 fpus;
+	u64 loads;
+	u64 stores;
+	u64 llsc;
+	u64 dsemul;
+};
+
+struct mips_r2br_emulator_stats {
+	u64 jrs;
+	u64 bltzl;
+	u64 bgezl;
+	u64 bltzll;
+	u64 bgezll;
+	u64 bltzall;
+	u64 bgezall;
+	u64 bltzal;
+	u64 bgezal;
+	u64 beql;
+	u64 bnel;
+	u64 blezl;
+	u64 bgtzl;
+};
+
+#ifdef CONFIG_DEBUG_FS
+
+#define MIPS_R2_STATS(M)						\
+do {									\
+	u32 nir;							\
+	int err;							\
+									\
+	preempt_disable();						\
+	__this_cpu_inc(mipsr2emustats.M);				\
+	err = __get_user(nir, (u32 __user *)regs->cp0_epc);		\
+	if (!err) {							\
+		if (nir == BREAK_MATH)					\
+			__this_cpu_inc(mipsr2bdemustats.M);		\
+	}								\
+	preempt_enable();						\
+} while (0)
+
+#define MIPS_R2BR_STATS(M)					\
+do {								\
+	preempt_disable();					\
+	__this_cpu_inc(mipsr2bremustats.M);			\
+	preempt_enable();					\
+} while (0)
+
+#else
+
+#define MIPS_R2_STATS(M)          do { } while (0)
+#define MIPS_R2BR_STATS(M)        do { } while (0)
+
+#endif /* CONFIG_DEBUG_FS */
+
+struct r2_decoder_table {
+	u32     mask;
+	u32     code;
+	int     (*func)(struct pt_regs *regs, u32 inst);
+};
+
+
+extern void do_trap_or_bp(struct pt_regs *regs, unsigned int code,
+			  const char *str);
+
+#ifndef CONFIG_MIPSR2_TO_R6_EMULATOR
+static int mipsr2_emulation;
+static __maybe_unused int mipsr2_decoder(struct pt_regs *regs, u32 inst) { return 0; };
+#else
+/* MIPS R2 Emulator ON/OFF */
+extern int mipsr2_emulation;
+extern int mipsr2_decoder(struct pt_regs *regs, u32 inst);
+#endif /* CONFIG_MIPSR2_TO_R6_EMULATOR */
+
+#define NO_R6EMU	(cpu_has_mips_r6 && !mipsr2_emulation)
+
+#endif /* __ASM_MIPS_R2_TO_R6_EMUL_H */