tools: kwboot: Do not send magic seq when changing baudrate back to 115200

After successful transfer of whole image only two things can happen:
- BootROM starts execution of data block, which changes UART baudrate
  back to 115200 Bd,
- board crashes and causes CPU reset

In both cases UART baudrate is reset to the default speed. So there is
no need to send special magic sequence to inform kwboot that baudrate is
going to be reset and kwboot does not need to wait for this event and
can do it immediately after BootROM acknowledges end of xmodem transfer.

Move ARM code for sending magic sequence from main baudrate change
section to binhdr_pre section which is executed only before changing
baudrate from the default value of 115200 Bd to some new value. Remove
kwboot code waiting for magic sequence after successful xmodem transfer.

Rationale: sometimes when using very high UART speeds, magic sequence is
damaged and kwboot fails at this last stage. Removal of this magic
sequence makes booting more stable.

Data transfer protocol (xmodem) is using checksums and retransmit, so it
already deals with possible errors on transfer line.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>

1 files changed, 60 insertions, 55 deletions

diff --git a/tools/kwboot.c b/tools/kwboot.c
index 359b43c0d8..bacca15301 100644
--- a/tools/kwboot.c
+++ b/tools/kwboot.c
@@ -81,23 +81,15 @@ struct kwboot_block {
 /* ARM code to change baudrate */
 static unsigned char kwboot_baud_code[] = {
 				/* ; #define UART_BASE 0xd0012000             */
-				/* ; #define THR       0x00                   */
 				/* ; #define DLL       0x00                   */
 				/* ; #define DLH       0x04                   */
 				/* ; #define LCR       0x0c                   */
 				/* ; #define   DLAB    0x80                   */
 				/* ; #define LSR       0x14                   */
-				/* ; #define   THRE    0x20                   */
 				/* ; #define   TEMT    0x40                   */
 				/* ; #define DIV_ROUND(a, b) ((a + b/2) / b)  */
 				/* ;                                          */
 				/* ; u32 set_baudrate(u32 old_b, u32 new_b) { */
-				/* ;   const u8 *str = "$baudratechange";     */
-				/* ;   u8 c;                                  */
-				/* ;   do {                                   */
-				/* ;       c = *str++;                        */
-				/* ;       writel(UART_BASE + THR, c);        */
-				/* ;   } while (c);                           */
 				/* ;   while                                  */
 				/* ;      (!(readl(UART_BASE + LSR) & TEMT)); */
 				/* ;   u32 lcr = readl(UART_BASE + LCR);      */
@@ -120,29 +112,6 @@ static unsigned char kwboot_baud_code[] = {
 	0x0d, 0x02, 0xa0, 0xe3, /* mov   r0, #0xd0000000                      */
 	0x12, 0x0a, 0x80, 0xe3, /* orr   r0, r0, #0x12000                     */
 
-				/*  ; r2 = address of preamble string         */
-	0xc8, 0x20, 0x8f, 0xe2, /* adr   r2, preamble                         */
-
-				/*  ; Send preamble string over UART          */
-				/* .Lloop_preamble:                           */
-				/*                                            */
-				/*  ; Wait until Transmitter Holding is Empty */
-				/* .Lloop_thre:                               */
-				/*  ; r1 = UART_BASE[LSR] & THRE              */
-	0x14, 0x10, 0x90, 0xe5, /* ldr   r1, [r0, #0x14]                      */
-	0x20, 0x00, 0x11, 0xe3, /* tst   r1, #0x20                            */
-	0xfc, 0xff, 0xff, 0x0a, /* beq   .Lloop_thre                          */
-
-				/*  ; Put character into Transmitter FIFO     */
-				/*  ; r1 = *r2++                              */
-	0x01, 0x10, 0xd2, 0xe4, /* ldrb  r1, [r2], #1                         */
-				/*  ; UART_BASE[THR] = r1                     */
-	0x00, 0x10, 0x80, 0xe5, /* str   r1, [r0, #0x0]                       */
-
-				/*  ; Loop until end of preamble string       */
-	0x00, 0x00, 0x51, 0xe3, /* cmp   r1, #0                               */
-	0xf8, 0xff, 0xff, 0x1a, /* bne   .Lloop_preamble                      */
-
 				/*  ; Wait until Transmitter FIFO is Empty    */
 				/* .Lloop_txempty:                            */
 				/*  ; r1 = UART_BASE[LSR] & TEMT              */
@@ -168,7 +137,7 @@ static unsigned char kwboot_baud_code[] = {
 
 				/*  ; Read old baudrate value                 */
 				/*  ; r2 = old_baudrate                       */
-	0x84, 0x20, 0x9f, 0xe5, /* ldr   r2, old_baudrate                     */
+	0x74, 0x20, 0x9f, 0xe5, /* ldr   r2, old_baudrate                     */
 
 				/*  ; Calculate base clock                    */
 				/*  ; r1 = r2 * r1                            */
@@ -176,7 +145,7 @@ static unsigned char kwboot_baud_code[] = {
 
 				/*  ; Read new baudrate value                 */
 				/*  ; r2 = new_baudrate                       */
-	0x80, 0x20, 0x9f, 0xe5, /* ldr   r2, new_baudrate                     */
+	0x70, 0x20, 0x9f, 0xe5, /* ldr   r2, new_baudrate                     */
 
 				/*  ; Calculate new Divisor Latch             */
 				/*  ; r1 = DIV_ROUND(r1, r2) =                */
@@ -225,14 +194,8 @@ static unsigned char kwboot_baud_code[] = {
 	0x00, 0x00, 0x51, 0xe3, /* cmp   r1, #0                               */
 	0xfc, 0xff, 0xff, 0x1a, /* bne   .Lloop_sleep                         */
 
-	0x05, 0x00, 0x00, 0xea, /* b     end                                  */
-
-				/*  ; Preamble string                         */
-				/* preamble:                                  */
-	0x24, 0x62, 0x61, 0x75, /* .asciz "$baudratechange"                   */
-	0x64, 0x72, 0x61, 0x74,
-	0x65, 0x63, 0x68, 0x61,
-	0x6e, 0x67, 0x65, 0x00,
+				/*  ; Jump to the end of execution            */
+	0x01, 0x00, 0x00, 0xea, /* b     end                                  */
 
 				/*  ; Placeholder for old baudrate value      */
 				/* old_baudrate:                              */
@@ -245,12 +208,66 @@ static unsigned char kwboot_baud_code[] = {
 				/* end:                                       */
 };
 
-/* ARM code for storing registers for future returning back to the bootrom */
+/* ARM code from binary header executed by BootROM before changing baudrate */
 static unsigned char kwboot_baud_code_binhdr_pre[] = {
+				/* ; #define UART_BASE 0xd0012000             */
+				/* ; #define THR       0x00                   */
+				/* ; #define LSR       0x14                   */
+				/* ; #define   THRE    0x20                   */
+				/* ;                                          */
+				/* ; void send_preamble(void) {               */
+				/* ;   const u8 *str = "$baudratechange";     */
+				/* ;   u8 c;                                  */
+				/* ;   do {                                   */
+				/* ;       while                              */
+				/* ;       ((readl(UART_BASE + LSR) & THRE)); */
+				/* ;       c = *str++;                        */
+				/* ;       writel(UART_BASE + THR, c);        */
+				/* ;   } while (c);                           */
+				/* ; }                                        */
+
+				/*  ; Preserve registers for BootROM          */
 	0xfe, 0x5f, 0x2d, 0xe9, /* push  { r1 - r12, lr }                     */
+
+				/*  ; r0 = UART_BASE                          */
+	0x0d, 0x02, 0xa0, 0xe3, /* mov   r0, #0xd0000000                      */
+	0x12, 0x0a, 0x80, 0xe3, /* orr   r0, r0, #0x12000                     */
+
+				/*  ; r2 = address of preamble string         */
+	0x00, 0x20, 0x8f, 0xe2, /* adr   r2, .Lstr_preamble                   */
+
+				/*  ; Skip preamble data section              */
+	0x03, 0x00, 0x00, 0xea, /* b     .Lloop_preamble                      */
+
+				/*  ; Preamble string                         */
+				/* .Lstr_preamble:                            */
+	0x24, 0x62, 0x61, 0x75, /* .asciz "$baudratechange"                   */
+	0x64, 0x72, 0x61, 0x74,
+	0x65, 0x63, 0x68, 0x61,
+	0x6e, 0x67, 0x65, 0x00,
+
+				/*  ; Send preamble string over UART          */
+				/* .Lloop_preamble:                           */
+				/*                                            */
+				/*  ; Wait until Transmitter Holding is Empty */
+				/* .Lloop_thre:                               */
+				/*  ; r1 = UART_BASE[LSR] & THRE              */
+	0x14, 0x10, 0x90, 0xe5, /* ldr   r1, [r0, #0x14]                      */
+	0x20, 0x00, 0x11, 0xe3, /* tst   r1, #0x20                            */
+	0xfc, 0xff, 0xff, 0x0a, /* beq   .Lloop_thre                          */
+
+				/*  ; Put character into Transmitter FIFO     */
+				/*  ; r1 = *r2++                              */
+	0x01, 0x10, 0xd2, 0xe4, /* ldrb  r1, [r2], #1                         */
+				/*  ; UART_BASE[THR] = r1                     */
+	0x00, 0x10, 0x80, 0xe5, /* str   r1, [r0, #0x0]                       */
+
+				/*  ; Loop until end of preamble string       */
+	0x00, 0x00, 0x51, 0xe3, /* cmp   r1, #0                               */
+	0xf8, 0xff, 0xff, 0x1a, /* bne   .Lloop_preamble                      */
 };
 
-/* ARM code for returning back to the bootrom */
+/* ARM code for returning from binary header back to BootROM */
 static unsigned char kwboot_baud_code_binhdr_post[] = {
 				/*  ; Return 0 - no error                     */
 	0x00, 0x00, 0xa0, 0xe3, /* mov   r0, #0                               */
@@ -1078,18 +1095,6 @@ kwboot_xmodem(int tty, const void *_img, size_t size, int baudrate)
 		return rc;
 
 	if (baudrate) {
-		char buf[sizeof(kwb_baud_magic)];
-
-		kwboot_printv("Waiting 1s for baudrate change magic\n");
-		rc = kwboot_tty_recv(tty, buf, sizeof(buf), 1000);
-		if (rc)
-			return rc;
-
-		if (memcmp(buf, kwb_baud_magic, sizeof(buf))) {
-			errno = EPROTO;
-			return -1;
-		}
-
 		kwboot_printv("\nChanging baudrate back to 115200 Bd\n\n");
 		rc = kwboot_tty_change_baudrate(tty, 115200);
 		if (rc)