[PATCH v2] scripts: kwboot: improve reliability on Armada XP

[Uwe Kleine-König]

This introduces several changes that improve pushing a boot image via
UART to an Armada XP based machine (Netgear RN 2120 with BootROM 1.20).
They were found by inspecting the source, the actual communication and
disassembling the boot ROM.

The changes are:
 - Don't use non-blocking open. This prevents trying to read the answer
   from the SoC before the magic sequence was sent.
 - Don't flush the input after each sending of the boot sequence as this
   might discard the SoC's reply.
 - A likely reason for a NAK is that sender and receiver are not synced
   on xmodem packet boundary. This happens easily when the host sends to
   many boot sequences. So on a NAK send 0xff to resync.
 - Shorten the time between two tries to send the magic string.
   This greatly improves the probabilty the string is sent while the SoC
   listens for it. This only works because of the previous changes.

Unfortunately this doesn't make sending reliable yet. I can enter UART
boot mode, but it is aborted after several packets, which I failed to
debug up to now.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
---
Changes since (implict) v1 sent with
Message-Id: 20160926081543.16088-1-u.kleine-koenig at pengutronix.de

 - mention that KWBOOT_MSG_RSP_TIMEO was made smaller
 - fix build warning about isprint()

Testing is still welcome of course.

 scripts/kwboot.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 63 insertions(+), 10 deletions(-)

diff --git a/scripts/kwboot.c b/scripts/kwboot.c
index 9b0d1d0602a0..943e800fd928 100644
--- a/scripts/kwboot.c
+++ b/scripts/kwboot.c
@@ -9,6 +9,7 @@
  *   2008. Chapter 24.2 "BootROM Firmware".
  */
 
+#include <ctype.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
@@ -35,7 +36,7 @@ static unsigned char kwboot_msg_debug[] = {
 };
 
 #define KWBOOT_MSG_REQ_DELAY	1000 /* ms */
-#define KWBOOT_MSG_RSP_TIMEO	1000 /* ms */
+#define KWBOOT_MSG_RSP_TIMEO	1 /* ms */
 
 /*
  * Xmodem Transfers
@@ -233,7 +234,7 @@ kwboot_open_tty(const char *path, speed_t speed)
 
 	rc = -1;
 
-	fd = open(path, O_RDWR|O_NOCTTY|O_NDELAY);
+	fd = open(path, O_RDWR | O_NOCTTY);
 	if (fd < 0)
 		goto out;
 
@@ -273,11 +274,11 @@ kwboot_bootmsg(int tty, void *msg)
 	else
 		kwboot_printv("Sending boot message. Please reboot the target...");
 
-	do {
-		rc = tcflush(tty, TCIOFLUSH);
-		if (rc)
-			break;
+	rc = tcflush(tty, TCIOFLUSH);
+	if (rc)
+		return rc;
 
+	do {
 		rc = kwboot_tty_send(tty, msg, 8);
 		if (rc) {
 			usleep(KWBOOT_MSG_REQ_DELAY * 1000);
@@ -285,12 +286,20 @@ kwboot_bootmsg(int tty, void *msg)
 		}
 
 		rc = kwboot_tty_recv(tty, &c, 1, KWBOOT_MSG_RSP_TIMEO);
-
-		kwboot_spinner();
+		while (!rc && c != NAK) {
+			if (c == '\\')
+				kwboot_printv("\\\\", c);
+			else if (isprint(c))
+				kwboot_printv("%c", c);
+			else
+				kwboot_printv("\\x%02hhx", c);
+
+			rc = kwboot_tty_recv(tty, &c, 1, KWBOOT_MSG_RSP_TIMEO);
+		}
 
 	} while (rc || c != NAK);
 
-	kwboot_printv("\n");
+	kwboot_printv("\nGot expected NAK\n");
 
 	return rc;
 }
@@ -349,6 +358,48 @@ kwboot_xm_makeblock(struct kwboot_block *block, const void *data,
 	return n;
 }
 
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
+static int
+kwboot_xm_resync(int fd)
+{
+	/*
+	 * When the SoC has a different perception of where the package boundary
+	 * is, just resending the packet doesn't help. To resync send 0xff until
+	 * we get another NAK.
+	 * The BootROM code (of the Armada XP at least) doesn't interpret 0xff
+	 * as a start of a package and sends a NAK for each 0xff when waiting
+	 * for SOH, so it's possible to send >1 byte without the SoC starting a
+	 * new frame.
+	 * When there is no response after sizeof(struct kwboot_block) bytes,
+	 * there is another problem.
+	 */
+	int rc;
+	char buf[sizeof(struct kwboot_block)];
+	unsigned interval = 1;
+	unsigned len;
+	char *p = buf;
+
+	memset(buf, 0xff, sizeof(buf));
+
+	while (interval <= sizeof(buf)) {
+		len = min(interval, buf + sizeof(buf) - p);
+		rc = kwboot_tty_send(fd, p, len);
+		if (rc)
+			return rc;
+
+		kwboot_tty_recv(fd, p, len, KWBOOT_BLK_RSP_TIMEO);
+		if (*p != 0xff)
+			/* got at least one char, if it's a NAK we're synced. */
+			return (*p == NAK);
+
+		p += len;
+		interval *= 2;
+	}
+
+	return 0;
+}
+
 static int
 kwboot_xm_sendblock(int fd, struct kwboot_block *block)
 {
@@ -371,7 +422,9 @@ kwboot_xm_sendblock(int fd, struct kwboot_block *block)
 
 		} while (c != ACK && c != NAK && c != CAN);
 
-		if (c != ACK)
+		if (c == NAK && kwboot_xm_resync(fd))
+			kwboot_progress(-1, 'S');
+		else if (c != ACK)
 			kwboot_progress(-1, '+');
 
 	} while (c == NAK && retries-- > 0);
-- 
2.9.3