ipmi:ssif: compare block number correctly for multi-part return messages

According to ipmi spec, block number is a number that is incremented,
starting with 0, for each new block of message data returned using the
middle transaction.

Here, the 'blocknum' is data[0] which always starts from zero(0) and
'ssif_info->multi_pos' starts from 1.
So, we need to add +1 to blocknum while comparing with multi_pos.

Fixes: 7d6380cd ("ipmi:ssif: Fix handling of multi-part return messages").
Reported-by: Kiran Kolukuluru <kirank@ami.com>
Signed-off-by: Kamlakant Patel <kamlakantp@marvell.com>
Message-Id: <1556106615-18722-1-git-send-email-kamlakantp@marvell.com>
[Also added a debug log if the block numbers don't match.]
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Cc: stable@vger.kernel.org # 4.4

drivers/char/ipmi/ipmi_ssif.c

@@ -727,12 +727,16 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 			/* End of read */
 			len = ssif_info->multi_len;
 			data = ssif_info->data;
-		} else if (blocknum != ssif_info->multi_pos) {
+		} else if (blocknum + 1 != ssif_info->multi_pos) {
 			/*
 			 * Out of sequence block, just abort.  Block
 			 * numbers start at zero for the second block,
 			 * but multi_pos starts at one, so the +1.
 			 */
+			if (ssif_info->ssif_debug & SSIF_DEBUG_MSG)
+				dev_dbg(&ssif_info->client->dev,
+					"Received message out of sequence, expected %u, got %u\n",
+					ssif_info->multi_pos - 1, blocknum);
 			result = -EIO;
 		} else {
 			ssif_inc_stat(ssif_info, received_message_parts);