scripts: kwboot: fix detection of timeout

In function kwboot_xm_sendblock() the loop that implements retrying to
send a boot block might be quit if kwboot_tty_send or kwboot_tty_recv
return a failure. In this case the value of the variable c that is
expected to hold the response byte is uninitialized and most likely
still holds an ACK from the previous call to kwboot_xm_sendblock().

So the right thing to do is not to clobber rc if it's already != 0.

The result of this patch in my current scenario is that kwboot dies with

	xmodem: Connection timed out

when the SoC stops replying instead of continuing to try sending the
remaining blocks which results in select() blocking for one second for
each block.

Fixes: 0535713bbfa0 ("scripts: add kwboot tool")
Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
--
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Gregory CLEMENT <gregory.clement@free-electrons.com>
Cc: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>

I also tried to increase the timeout, but without success :-(. Will test
a different USB-to-RS232 adapter ...
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 16 insertions, 14 deletions

diff --git a/scripts/kwboot.c b/scripts/kwboot.c
index e06866052b..46328d8ed0 100644
--- a/scripts/kwboot.c
+++ b/scripts/kwboot.c
@@ -376,21 +376,23 @@ kwboot_xm_sendblock(int fd, struct kwboot_block *block)
 
 	} while (c == NAK && retries-- > 0);
 
-	rc = -1;
+	if (!rc) {
+		rc = -1;
 
-	switch (c) {
-	case ACK:
-		rc = 0;
-		break;
-	case NAK:
-		errno = EBADMSG;
-		break;
-	case CAN:
-		errno = ECANCELED;
-		break;
-	default:
-		errno = EPROTO;
-		break;
+		switch (c) {
+		case ACK:
+			rc = 0;
+			break;
+		case NAK:
+			errno = EBADMSG;
+			break;
+		case CAN:
+			errno = ECANCELED;
+			break;
+		default:
+			errno = EPROTO;
+			break;
+		}
 	}
 
 	return rc;