AT91: Fix AT91SAM9G20 reset as per the errata in the data sheet

If the SDRAM is not cleanly shutdown before reset it can be left driving
the bus, which then stops the bootloader booting from NAND.

Signed-off-by: Peter Horton <phorton@bitbox.co.uk>
[nicolas.ferre@atmel.com: change file header line order]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/Makefile

@@ -16,7 +16,7 @@ obj-$(CONFIG_ARCH_AT91SAM9261)	+= at91sam9261.o at91sam926x_time.o at91sam9261_d
 obj-$(CONFIG_ARCH_AT91SAM9G10)	+= at91sam9261.o at91sam926x_time.o at91sam9261_devices.o sam9_smc.o
 obj-$(CONFIG_ARCH_AT91SAM9263)	+= at91sam9263.o at91sam926x_time.o at91sam9263_devices.o sam9_smc.o
 obj-$(CONFIG_ARCH_AT91SAM9RL)	+= at91sam9rl.o at91sam926x_time.o at91sam9rl_devices.o sam9_smc.o
-obj-$(CONFIG_ARCH_AT91SAM9G20)	+= at91sam9260.o at91sam926x_time.o at91sam9260_devices.o sam9_smc.o
+obj-$(CONFIG_ARCH_AT91SAM9G20)	+= at91sam9260.o at91sam926x_time.o at91sam9260_devices.o sam9_smc.o at91sam9g20_reset.o
 obj-$(CONFIG_ARCH_AT91SAM9G45)	+= at91sam9g45.o at91sam926x_time.o at91sam9g45_devices.o sam9_smc.o
 obj-$(CONFIG_ARCH_AT91CAP9)	+= at91cap9.o at91sam926x_time.o at91cap9_devices.o sam9_smc.o
 obj-$(CONFIG_ARCH_AT572D940HF)  += at572d940hf.o at91sam926x_time.o at572d940hf_devices.o sam9_smc.o

arch/arm/mach-at91/at91sam9260.c

@@ -25,6 +25,8 @@
 #include "generic.h"
 #include "clock.h"
 
+extern void at91sam9g20_reset(void);
+
 static struct map_desc at91sam9260_io_desc[] __initdata = {
 	{
 		.virtual	= AT91_VA_BASE_SYS,
@@ -327,7 +329,11 @@ void __init at91sam9260_initialize(unsigned long main_clock)
 	else
 		iotable_init(at91sam9260_sram_desc, ARRAY_SIZE(at91sam9260_sram_desc));
 
-	at91_arch_reset = at91sam9260_reset;
+	if (cpu_is_at91sam9g20())
+		at91_arch_reset = at91sam9g20_reset;
+	else
+		at91_arch_reset = at91sam9260_reset;
+
 	pm_power_off = at91sam9260_poweroff;
 	at91_extern_irq = (1 << AT91SAM9260_ID_IRQ0) | (1 << AT91SAM9260_ID_IRQ1)
 			| (1 << AT91SAM9260_ID_IRQ2);

arch/arm/mach-at91/at91sam9g20_reset.S

@@ -0,0 +1,55 @@
+/*
+ * reset AT91SAM9G20 as per errata
+ *
+ * (C) BitBox Ltd 2010
+ *
+ * unless the SDRAM is cleanly shutdown before we hit the
+ * reset register it can be left driving the data bus and
+ * killing the chance of a subsequent boot from NAND
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#define CP15_CR_I			(1 << 12)
+
+#define SYS_VIRT_OFS			(-0x01000000)
+
+#define SDRAMC_BASE			(SYS_VIRT_OFS + 0xffffea00)
+#define  SDRAMC_TR			0x0004
+#define  SDRAMC_LPR			0x0010
+#define   SDRAMC_LPCB_POWER_DOWN	2
+
+#define RSTC_BASE			(SYS_VIRT_OFS + 0xfffffd00)
+#define  RSTC_CR			0x0000
+#define   RSTC_PROCRST			(1 << 0)
+#define   RSTC_PERRST			(1 << 2)
+#define   RSTC_KEY			(0xa5 << 24)
+
+			.arm
+
+			.globl	at91sam9g20_reset
+
+at91sam9g20_reset:	mov	r0, #0
+			mcr	p15, 0, r0, c7, c5, 0	@ flush I-cache
+
+			mrc	p15, 0, r0, c1, c0, 0
+			orr	r0, r0, #CP15_CR_I
+			mcr	p15, 0, r0, c1, c0, 0	@ enable I-cache
+
+			ldr	r0, =SDRAMC_BASE	@ preload constants
+			ldr	r1, =RSTC_BASE
+
+			mov	r2, #1
+			mov	r3, #SDRAMC_LPCB_POWER_DOWN
+			ldr	r4, =RSTC_KEY | RSTC_PERRST | RSTC_PROCRST
+
+			.balign	32			@ align to cache line
+
+			str	r2, [r0, #SDRAMC_TR]	@ disable SDRAM access
+			str	r3, [r0, #SDRAMC_LPR]	@ power down SDRAM
+			str	r4, [r1, #RSTC_CR]	@ reset processor
+
+			b	.