mfd: cros ec: spi: Fix "in progress" error signaling

For host commands that take a long time to process, cros ec can return
early by signaling a EC_RES_IN_PROGRESS result. The host must then poll
status with EC_CMD_GET_COMMS_STATUS until completion of the command.

None of the above applies when data link errors are encountered. When
errors such as EC_SPI_PAST_END are encountered during command
transmission, it usually means the command was not received by the EC.
Treating such errors as if they were 'EC_RES_IN_PROGRESS' results is
almost always the wrong decision, and can result in host commands
silently being lost.
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/cros_ec_spi.c

@@ -377,6 +377,7 @@ static int cros_ec_pkt_xfer_spi(struct cros_ec_device *ec_dev,
 	u8 *ptr;
 	u8 *rx_buf;
 	u8 sum;
+	u8 rx_byte;
 	int ret = 0, final_ret;
 
 	len = cros_ec_prepare_tx(ec_dev, ec_msg);
@@ -421,24 +422,21 @@ static int cros_ec_pkt_xfer_spi(struct cros_ec_device *ec_dev,
 	if (!ret) {
 		/* Verify that EC can process command */
 		for (i = 0; i < len; i++) {
-			switch (rx_buf[i]) {
-			case EC_SPI_PAST_END:
-			case EC_SPI_RX_BAD_DATA:
-			case EC_SPI_NOT_READY:
-				ret = -EAGAIN;
-				ec_msg->result = EC_RES_IN_PROGRESS;
-			default:
+			rx_byte = rx_buf[i];
+			if (rx_byte == EC_SPI_PAST_END  ||
+			    rx_byte == EC_SPI_RX_BAD_DATA ||
+			    rx_byte == EC_SPI_NOT_READY) {
+				ret = -EREMOTEIO;
 				break;
 			}
-			if (ret)
-				break;
 		}
+	}
+
 	if (!ret)
 		ret = cros_ec_spi_receive_packet(ec_dev,
 				ec_msg->insize + sizeof(*response));
-	} else {
+	else
 		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
-	}
 
 	final_ret = terminate_request(ec_dev);
 
@@ -508,6 +506,7 @@ static int cros_ec_cmd_xfer_spi(struct cros_ec_device *ec_dev,
 	int i, len;
 	u8 *ptr;
 	u8 *rx_buf;
+	u8 rx_byte;
 	int sum;
 	int ret = 0, final_ret;
 
@@ -544,24 +543,21 @@ static int cros_ec_cmd_xfer_spi(struct cros_ec_device *ec_dev,
 	if (!ret) {
 		/* Verify that EC can process command */
 		for (i = 0; i < len; i++) {
-			switch (rx_buf[i]) {
-			case EC_SPI_PAST_END:
-			case EC_SPI_RX_BAD_DATA:
-			case EC_SPI_NOT_READY:
-				ret = -EAGAIN;
-				ec_msg->result = EC_RES_IN_PROGRESS;
-			default:
+			rx_byte = rx_buf[i];
+			if (rx_byte == EC_SPI_PAST_END  ||
+			    rx_byte == EC_SPI_RX_BAD_DATA ||
+			    rx_byte == EC_SPI_NOT_READY) {
+				ret = -EREMOTEIO;
 				break;
 			}
-			if (ret)
-				break;
 		}
+	}
+
 	if (!ret)
 		ret = cros_ec_spi_receive_response(ec_dev,
 				ec_msg->insize + EC_MSG_TX_PROTO_BYTES);
-	} else {
+	else
 		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
-	}
 
 	final_ret = terminate_request(ec_dev);