powerpc sstep: Add support for prefixed fixed-point arithmetic

This adds emulation support for the following prefixed Fixed-Point
Arithmetic instructions:
  * Prefixed Add Immediate (paddi)
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Reviewed-by: Balamuruhan S <bala24@linux.ibm.com>
[mpe: Squash in get_op() usage]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200506034050.24806-31-jniethe5@gmail.com

arch/powerpc/lib/sstep.c

@@ -1338,6 +1338,26 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 
 	switch (opcode) {
 #ifdef __powerpc64__
+	case 1:
+		prefix_r = word & (1ul << 20);
+		ra = (suffix >> 16) & 0x1f;
+		rd = (suffix >> 21) & 0x1f;
+		op->reg = rd;
+		op->val = regs->gpr[rd];
+		suffixopcode = get_op(suffix);
+		prefixtype = (word >> 24) & 0x3;
+		switch (prefixtype) {
+		case 2:
+			if (prefix_r && ra)
+				return 0;
+			switch (suffixopcode) {
+			case 14:	/* paddi */
+				op->type = COMPUTE | PREFIXED;
+				op->val = mlsd_8lsd_ea(word, suffix, regs);
+				goto compute_done;
+			}
+		}
+		break;
 	case 2:		/* tdi */
 		if (rd & trap_compare(regs->gpr[ra], (short) word))
 			goto trap;