MIPS: Emulate the new MIPS R6 BOVC, BEQC and BEQZALC instructions

MIPS R6 uses the <R6 ADDI opcode for the new BOVC, BEQC and
BEQZALC instructions.
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>

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

@@ -21,7 +21,7 @@
 enum major_op {
 	spec_op, bcond_op, j_op, jal_op,
 	beq_op, bne_op, blez_op, bgtz_op,
-	addi_op, addiu_op, slti_op, sltiu_op,
+	addi_op, cbcond0_op = addi_op, addiu_op, slti_op, sltiu_op,
 	andi_op, ori_op, xori_op, lui_op,
 	cop0_op, cop1_op, cop2_op, cop1x_op,
 	beql_op, bnel_op, blezl_op, bgtzl_op,

arch/mips/kernel/branch.c

@@ -790,6 +790,17 @@ int __compute_return_epc_for_insn(struct pt_regs *regs,
 		regs->cp0_epc += 8;
 		break;
 #endif
+	case cbcond0_op:
+		/* Only valid for MIPS R6 */
+		if (!cpu_has_mips_r6) {
+			ret = -SIGILL;
+			break;
+		}
+		/* Compact branches: bovc, beqc, beqzalc */
+		if (insn.i_format.rt && !insn.i_format.rs)
+			regs->regs[31] = epc + 4;
+		regs->cp0_epc += 8;
+		break;
 	}
 
 	return ret;

arch/mips/math-emu/cp1emu.c

@@ -623,6 +623,15 @@ static int isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
 				dec_insn.pc_inc +
 				dec_insn.next_pc_inc;
 		return 1;
+	case cbcond0_op:
+		if (!cpu_has_mips_r6)
+			break;
+		if (insn.i_format.rt && !insn.i_format.rs)
+			regs->regs[31] = regs->cp0_epc + 4;
+		*contpc = regs->cp0_epc + dec_insn.pc_inc +
+			dec_insn.next_pc_inc;
+
+		return 1;
 #ifdef CONFIG_CPU_CAVIUM_OCTEON
 	case lwc2_op: /* This is bbit0 on Octeon */
 		if ((regs->regs[insn.i_format.rs] & (1ull<<insn.i_format.rt)) == 0)