fsi: occ: Improve response status checking

If the driver sequence number coincidentally equals the previous
command response sequence number, the driver may proceed with
fetching the entire buffer before the OCC has processed the current
command. To be sure the correct response is obtained, check the
command type and also retry if any of the response parameters have
changed when the rest of the buffer is fetched. Also initialize the
driver with a random sequence number in order to reduce the chances
of this happening.

Signed-off-by: Eddie James <[e-mail]>
Reviewed-by: Joel Stanley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Joel Stanley <[e-mail]>

drivers/fsi/fsi-occ.c

···
 	return rc;
 }
 
+static bool fsi_occ_response_not_ready(struct occ_response *resp, u8 seq_no,
+				       u8 cmd_type)
+{
+	return resp->return_status == OCC_RESP_CMD_IN_PRG ||
+		resp->return_status == OCC_RESP_CRIT_INIT ||
+		resp->seq_no != seq_no || resp->cmd_type != cmd_type;
+}
+
 int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
 		   void *response, size_t *resp_len)
 {
···
 	struct occ_response *resp = response;
 	size_t user_resp_len = *resp_len;
 	u8 seq_no;
+	u8 cmd_type;
 	u16 checksum = 0;
 	u16 resp_data_length;
 	const u8 *byte_request = (const u8 *)request;
-	unsigned long start;
+	unsigned long end;
 	int rc;
 	size_t i;
 
···
 		dev_dbg(dev, "Bad resplen %zd\n", user_resp_len);
 		return -EINVAL;
 	}
+
+	cmd_type = byte_request[1];
 
 	/* Checksum the request, ignoring first byte (sequence number). */
 	for (i = 1; i < req_len - 2; ++i)
···
 	if (rc)
 		goto done;
 
-	/* Read occ response header */
-	start = jiffies;
-	do {
+	end = jiffies + timeout;
+	while (true) {
+		/* Read occ response header */
 		rc = occ_getsram(occ, 0, resp, 8);
 		if (rc)
 			goto done;
 
-		if (resp->return_status == OCC_RESP_CMD_IN_PRG ||
-		    resp->return_status == OCC_RESP_CRIT_INIT ||
-		    resp->seq_no != seq_no) {
-			rc = -ETIMEDOUT;
-
-			if (time_after(jiffies, start + timeout)) {
-				dev_err(occ->dev, "resp timeout status=%02x "
-					"resp seq_no=%d our seq_no=%d\n",
+		if (fsi_occ_response_not_ready(resp, seq_no, cmd_type)) {
+			if (time_after(jiffies, end)) {
+				dev_err(occ->dev,
+					"resp timeout status=%02x seq=%d cmd=%d, our seq=%d cmd=%d\n",
 					resp->return_status, resp->seq_no,
-					seq_no);
+					resp->cmd_type, seq_no, cmd_type);
+				rc = -ETIMEDOUT;
 				goto done;
 			}
 
 			set_current_state(TASK_UNINTERRUPTIBLE);
 			schedule_timeout(wait_time);
+		} else {
+			/* Extract size of response data */
+			resp_data_length =
+				get_unaligned_be16(&resp->data_length);
+
+			/*
+			 * Message size is data length + 5 bytes header + 2
+			 * bytes checksum
+			 */
+			if ((resp_data_length + 7) > user_resp_len) {
+				rc = -EMSGSIZE;
+				goto done;
+			}
+
+			/*
+			 * Get the entire response including the header again,
+			 * in case it changed
+			 */
+			if (resp_data_length > 1) {
+				rc = occ_getsram(occ, 0, resp,
+						 resp_data_length + 7);
+				if (rc)
+					goto done;
+
+				if (!fsi_occ_response_not_ready(resp, seq_no,
+								cmd_type))
+					break;
+			} else {
+				break;
+			}
 		}
-	} while (rc);
-
-	/* Extract size of response data */
-	resp_data_length = get_unaligned_be16(&resp->data_length);
-
-	/* Message size is data length + 5 bytes header + 2 bytes checksum */
-	if ((resp_data_length + 7) > user_resp_len) {
-		rc = -EMSGSIZE;
-		goto done;
 	}
 
 	dev_dbg(dev, "resp_status=%02x resp_data_len=%d\n",
 		resp->return_status, resp_data_length);
-
-	/* Grab the rest */
-	if (resp_data_length > 1) {
-		/* already got 3 bytes resp, also need 2 bytes checksum */
-		rc = occ_getsram(occ, 8, &resp->data[3], resp_data_length - 1);
-		if (rc)
-			goto done;
-	}
 
 	occ->client_response_size = resp_data_length + 7;
 	rc = occ_verify_checksum(occ, resp, resp_data_length);
···
 	occ->version = (uintptr_t)of_device_get_match_data(dev);
 	occ->dev = dev;
 	occ->sbefifo = dev->parent;
-	occ->sequence_number = 1;
+	/*
+	 * Quickly derive a pseudo-random number from jiffies so that
+	 * re-probing the driver doesn't accidentally overlap sequence numbers.
+	 */
+	occ->sequence_number = (u8)((jiffies % 0xff) + 1);
 	mutex_init(&occ->occ_lock);
 
 	if (dev->of_node) {