platform/chrome: correct cros_ec_prepare_tx() usage

cros_ec_prepare_tx() returns either:
- >= 0 for number of prepared bytes.
- < 0 for -errno.

Correct the comment and make sure all callers check the return code.
Reviewed-by: NGuenter Roeck <groeck@chromium.org>
Signed-off-by: NTzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220513044143.1045728-3-tzungbi@kernel.org

drivers/platform/chrome/cros_ec_i2c.c

@@ -89,6 +89,8 @@ static int cros_ec_pkt_xfer_i2c(struct cros_ec_device *ec_dev,
 
 	ec_dev->dout++;
 	ret = cros_ec_prepare_tx(ec_dev, msg);
+	if (ret < 0)
+		goto done;
 	ec_dev->dout--;
 
 	/* send command to EC and read answer */

drivers/platform/chrome/cros_ec_ishtp.c

@@ -521,7 +521,9 @@ static int cros_ec_pkt_xfer_ish(struct cros_ec_device *ec_dev,
 	out_msg->hdr.status = 0;
 
 	ec_dev->dout += OUT_MSG_EC_REQUEST_PREAMBLE;
-	cros_ec_prepare_tx(ec_dev, msg);
+	rv = cros_ec_prepare_tx(ec_dev, msg);
+	if (rv < 0)
+		goto end_error;
 	ec_dev->dout -= OUT_MSG_EC_REQUEST_PREAMBLE;
 
 	dev_dbg(dev,

drivers/platform/chrome/cros_ec_lpc.c

@@ -147,6 +147,8 @@ static int cros_ec_pkt_xfer_lpc(struct cros_ec_device *ec,
 	u8 *dout;
 
 	ret = cros_ec_prepare_tx(ec, msg);
+	if (ret < 0)
+		goto done;
 
 	/* Write buffer */
 	cros_ec_lpc_ops.write(EC_LPC_ADDR_HOST_PACKET, ret, ec->dout);

drivers/platform/chrome/cros_ec_proto.c

@@ -164,7 +164,7 @@ static int send_command(struct cros_ec_device *ec_dev,
  * only SPI uses it. Once LPC uses the same protocol it can start using it.
  * I2C could use it now, with a refactor of the existing code.
  *
- * Return: 0 on success or negative error code.
+ * Return: number of prepared bytes on success or negative error code.
  */
 int cros_ec_prepare_tx(struct cros_ec_device *ec_dev,
 		       struct cros_ec_command *msg)

drivers/platform/chrome/cros_ec_rpmsg.c

@@ -89,6 +89,8 @@ static int cros_ec_pkt_xfer_rpmsg(struct cros_ec_device *ec_dev,
 
 	ec_msg->result = 0;
 	len = cros_ec_prepare_tx(ec_dev, ec_msg);
+	if (len < 0)
+		return len;
 	dev_dbg(ec_dev->dev, "prepared, len=%d\n", len);
 
 	reinit_completion(&ec_rpmsg->xfer_ack);

drivers/platform/chrome/cros_ec_spi.c

@@ -401,6 +401,8 @@ static int do_cros_ec_pkt_xfer_spi(struct cros_ec_device *ec_dev,
 	unsigned long delay;
 
 	len = cros_ec_prepare_tx(ec_dev, ec_msg);
+	if (len < 0)
+		return len;
 	dev_dbg(ec_dev->dev, "prepared, len=%d\n", len);
 
 	/* If it's too soon to do another transaction, wait */
@@ -544,6 +546,8 @@ static int do_cros_ec_cmd_xfer_spi(struct cros_ec_device *ec_dev,
 	unsigned long delay;
 
 	len = cros_ec_prepare_tx(ec_dev, ec_msg);
+	if (len < 0)
+		return len;
 	dev_dbg(ec_dev->dev, "prepared, len=%d\n", len);
 
 	/* If it's too soon to do another transaction, wait */