MIPS: Emulate the new MIPS R6 branch compact (BC) instruction

MIPS R6 uses the <R6 LWC2 opcode for the new BC instruction.
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>

arch/mips/include/uapi/asm/inst.h

@@ -31,7 +31,7 @@ enum major_op {
 	lbu_op, lhu_op, lwr_op, lwu_op,
 	sb_op, sh_op, swl_op, sw_op,
 	sdl_op, sdr_op, swr_op, cache_op,
-	ll_op, lwc1_op, lwc2_op, pref_op,
+	ll_op, lwc1_op, lwc2_op, bc6_op = lwc2_op, pref_op,
 	lld_op, ldc1_op, ldc2_op, ld_op,
 	sc_op, swc1_op, swc2_op, major_3b_op,
 	scd_op, sdc1_op, sdc2_op, sd_op

arch/mips/kernel/branch.c

@@ -780,6 +780,15 @@ int __compute_return_epc_for_insn(struct pt_regs *regs,
 			epc += 8;
 		regs->cp0_epc = epc;
 		break;
+#else
+	case bc6_op:
+		/* Only valid for MIPS R6 */
+		if (!cpu_has_mips_r6) {
+			ret = -SIGILL;
+			break;
+		}
+		regs->cp0_epc += 8;
+		break;
 #endif
 	}
 

arch/mips/math-emu/cp1emu.c

@@ -648,6 +648,19 @@ static int isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
 		else
 			*contpc = regs->cp0_epc + 8;
 		return 1;
+#else
+	case bc6_op:
+		/*
+		 * Only valid for MIPS R6 but we can still end up
+		 * here from a broken userland so just tell emulator
+		 * this is not a branch and let it break later on.
+		 */
+		if  (!cpu_has_mips_r6)
+			break;
+		*contpc = regs->cp0_epc + dec_insn.pc_inc +
+			dec_insn.next_pc_inc;
+
+		return 1;
 #endif
 	case cop0_op:
 	case cop1_op: