m68k/atari: fix SCC initialization for debug console

Fix SCC initialization for Atari as was previously fixed for Mac. It's
probably not practical to share more code but some attempt is made to
align the Mac and Atari variants.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/kernel/head.S

@@ -2722,6 +2722,7 @@ func_return	get_new_page
 #define MAC_USE_SCC_B /* Printer port */
 
 #if defined(MAC_USE_SCC_A) || defined(MAC_USE_SCC_B)
+/* Initialisation table for SCC with 3.6864 MHz PCLK */
 L(scc_initable_mac):
 	.byte	4,0x44		/* x16, 1 stopbit, no parity */
 	.byte	3,0xc0		/* receiver: 8 bpc */
@@ -2744,14 +2745,12 @@ L(scc_initable_mac):
 #define USE_MFP
 
 #if defined(USE_SCC_A) || defined(USE_SCC_B)
-#define USE_SCC
-/* Initialisation table for SCC */
-L(scc_initable):
-	.byte	9,12		/* Reset */
+/* Initialisation table for SCC with 7.9872 MHz PCLK */
+/* PCLK == 8.0539 gives baud == 9680.1 */
+L(scc_initable_atari):
 	.byte	4,0x44		/* x16, 1 stopbit, no parity */
 	.byte	3,0xc0		/* receiver: 8 bpc */
 	.byte	5,0xe2		/* transmitter: 8 bpc, assert dtr/rts */
-	.byte	9,0		/* no interrupts */
 	.byte	10,0		/* NRZ */
 	.byte	11,0x50		/* use baud rate generator */
 	.byte	12,24,13,0	/* 9600 baud */
@@ -2800,7 +2799,7 @@ LMFP_UDR     = 0xfffa2f
  */
 
 /*
- * Initialize serial port hardware for 9600/8/1
+ * Initialize serial port hardware
  */
 func_start	serial_init,%d0/%d1/%a0/%a1
 	/*
@@ -2810,7 +2809,7 @@ func_start	serial_init,%d0/%d1/%a0/%a1
 	 *		d0 = boot info offset
 	 *	CONFIG_ATARI
 	 *		a0 = address of SCC
-	 *		a1 = Liobase address/address of scc_initable
+	 *		a1 = Liobase address/address of scc_initable_atari
 	 *		d0 = init data for serial port
 	 *	CONFIG_MAC
 	 *		a0 = address of SCC
@@ -2846,9 +2845,21 @@ func_start	serial_init,%d0/%d1/%a0/%a1
 	moveb	%a1@(LPSG_READ),%d0
 	bset	#5,%d0
 	moveb	%d0,%a1@(LPSG_WRITE)
-#elif defined(USE_SCC)
+#elif defined(USE_SCC_A) || defined(USE_SCC_B)
 	lea	%a1@(LSCC_CTRL),%a0
-	lea	%pc@(L(scc_initable)),%a1
+	/* Reset SCC register pointer */
+	moveb	%a0@,%d0
+	/* Reset SCC device: write register pointer then register value */
+	moveb	#9,%a0@
+	moveb	#0xc0,%a0@
+	/* Wait for 5 PCLK cycles, which is about 63 CPU cycles */
+	/* 5 / 7.9872 MHz = approx. 0.63 us = 63 / 100 MHz */
+	movel	#32,%d0
+2:
+	subq	#1,%d0
+	jne	2b
+	/* Initialize channel */
+	lea	%pc@(L(scc_initable_atari)),%a1
 2:	moveb	%a1@+,%d0
 	jmi	3f
 	moveb	%d0,%a0@
@@ -3017,7 +3028,7 @@ func_start	serial_putc,%d0/%d1/%a0/%a1
 	nop
 	bset	#5,%d0
 	moveb	%d0,%a1@(LPSG_WRITE)
-#elif defined(USE_SCC)
+#elif defined(USE_SCC_A) || defined(USE_SCC_B)
 3:	btst	#2,%a1@(LSCC_CTRL)
 	jeq	3b
 	moveb	%d0,%a1@(LSCC_DATA)