[ARM] 4412/1: S3C2412: reset errata fix

The S3C2412 has an reset-errata where the clock
may cause a glitch switching back to EXTCLK. We
force a switch to EXTCLK before writing the
reset register to force use of the CLKCON sync
logic to properly switch.

Fix problem reported by Matthieu Castet.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-s3c2412/s3c2412.c

@@ -16,6 +16,7 @@
 #include <linux/list.h>
 #include <linux/timer.h>
 #include <linux/init.h>
+#include <linux/delay.h>
 #include <linux/sysdev.h>
 #include <linux/serial_core.h>
 #include <linux/platform_device.h>
@@ -29,6 +30,7 @@
 #include <asm/io.h>
 #include <asm/irq.h>
 
+#include <asm/arch/reset.h>
 #include <asm/arch/idle.h>
 
 #include <asm/arch/regs-clock.h>
@@ -38,6 +40,7 @@
 #include <asm/arch/regs-gpioj.h>
 #include <asm/arch/regs-dsc.h>
 #include <asm/arch/regs-spi.h>
+#include <asm/arch/regs-s3c2412.h>
 
 #include <asm/plat-s3c24xx/s3c2412.h>
 #include <asm/plat-s3c24xx/cpu.h>
@@ -106,6 +109,23 @@ static void s3c2412_idle(void)
 	cpu_do_idle();
 }
 
+static void s3c2412_hard_reset(void)
+{
+	/* errata "Watch-dog/Software Reset Problem" specifies that
+	 * this reset must be done with the SYSCLK sourced from
+	 * EXTCLK instead of FOUT to avoid a glitch in the reset
+	 * mechanism.
+	 *
+	 * See the watchdog section of the S3C2412 manual for more
+	 * information on this fix.
+	 */
+
+	__raw_writel(0x00, S3C2412_CLKSRC);
+	__raw_writel(S3C2412_SWRST_RESET, S3C2412_SWRST);
+
+	mdelay(1);
+}
+
 /* s3c2412_map_io
  *
  * register the standard cpu IO areas, and any passed in from the
@@ -122,6 +142,10 @@ void __init s3c2412_map_io(struct map_desc *mach_desc, int mach_size)
 
 	s3c24xx_idle = s3c2412_idle;
 
+	/* set custom reset hook */
+
+	s3c24xx_reset_hook = s3c2412_hard_reset;
+
 	/* register our io-tables */
 
 	iotable_init(s3c2412_iodesc, ARRAY_SIZE(s3c2412_iodesc));

include/asm-arm/arch-s3c2410/regs-s3c2412.h

+/* linux/include/asm-arm/arch-s3c2410/regs-s3c2412.h
+ *
+ * Copyright 2007 Simtec Electronics
+ *	http://armlinux.simtec.co.uk/
+ *	Ben Dooks <ben@simtec.co.uk>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * S3C2412 specific register definitions
+*/
+
+#ifndef __ASM_ARCH_REGS_S3C2412_H
+#define __ASM_ARCH_REGS_S3C2412_H "s3c2412"
+
+#define S3C2412_SWRST		(S3C24XX_VA_CLKPWR + 0x30)
+#define S3C2412_SWRST_RESET	(0x533C2412)
+
+#endif	/* __ASM_ARCH_REGS_S3C2412_H */
+