[PATCH] platform/chrome: cros_ec_uart: fix negative type promoted to high

[Tzung-Bi Shih <tzungbi@kernel.org>]

serdev_device_write_buf() returns negative numbers on errors.  When
the return value compares to unsigned integer `len`, it promotes to
quite large positive number.

Fix it.

Fixes: 04a8bdd135cc ("platform/chrome: cros_ec_uart: Add transport layer")
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
Reported in https://lore.kernel.org/chrome-platform/Y7fhw4S7Tb0GcHMF@kili/T/#u.

 drivers/platform/chrome/cros_ec_uart.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec_uart.c b/drivers/platform/chrome/cros_ec_uart.c
index 6916069f1599..788246559bbb 100644
--- a/drivers/platform/chrome/cros_ec_uart.c
+++ b/drivers/platform/chrome/cros_ec_uart.c
@@ -149,9 +149,10 @@ static int cros_ec_uart_pkt_xfer(struct cros_ec_device *ec_dev,
 	resp->status = 0;
 
 	ret = serdev_device_write_buf(serdev, ec_dev->dout, len);
-	if (ret < len) {
+	if (ret < 0 || ret < len) {
 		dev_err(ec_dev->dev, "Unable to write data\n");
-		ret = -EIO;
+		if (ret >= 0)
+			ret = -EIO;
 		goto exit;
 	}
 
-- 
2.39.0.314.g84b9a713c41-goog