microblaze: Do not copy reset vectors/manual reset vector setup

Reset vector can be setup by bootloader and kernel doens't need
to touch it. If you require to setup reset vector, please use
CONFIG_MANUAL_RESET_VECTOR throught menuconfig.
It is not possible to setup address 0x0 as reset address because
make no sense to set it up at all.

Signed-off-by: Michal Simek <monstr@monstr.eu>
Signed-off-by: John Williams <john.williams@petalogix.com>

arch/microblaze/Kconfig

@@ -184,6 +184,17 @@ config LOWMEM_SIZE
 	hex "Maximum low memory size (in bytes)" if LOWMEM_SIZE_BOOL
 	default "0x30000000"
 
+config MANUAL_RESET_VECTOR
+	hex "Microblaze reset vector address setup"
+	default "0x0"
+	help
+	  Set this option to have the kernel override the CPU Reset vector.
+	  If zero, no change will be made to the MicroBlaze reset vector at
+	  address 0x0.
+	  If non-zero, a jump instruction to this address, will be written
+	  to the reset vector at address 0x0.
+	  If you are unsure, set it to default value 0x0.
+
 config KERNEL_START_BOOL
 	bool "Set custom kernel base address"
 	depends on ADVANCED_OPTIONS

arch/microblaze/kernel/entry.S

@@ -993,11 +993,10 @@ ENTRY(_reset)
 	/* These are compiled and loaded into high memory, then
 	 * copied into place in mach_early_setup */
 	.section	.init.ivt, "ax"
+#if CONFIG_MANUAL_RESET_VECTOR
 	.org	0x0
-	/* this is very important - here is the reset vector */
-	/* in current MMU branch you don't care what is here - it is
-	 * used from bootloader site - but this is correct for FS-BOOT */
-	brai	0x70
+	brai	CONFIG_MANUAL_RESET_VECTOR
+#endif
 	.org	0x8
 	brai	TOPHYS(_user_exception); /* syscall handler */
 	.org	0x10

arch/microblaze/kernel/setup.c

@@ -95,7 +95,8 @@ inline unsigned get_romfs_len(unsigned *addr)
 void __init machine_early_init(const char *cmdline, unsigned int ram,
 		unsigned int fdt, unsigned int msr)
 {
-	unsigned long *src, *dst = (unsigned long *)0x0;
+	unsigned long *src, *dst;
+	unsigned int offset = 0;
 
 	/* If CONFIG_MTD_UCLINUX is defined, assume ROMFS is at the
 	 * end of kernel. There are two position which we want to check.
@@ -168,7 +169,14 @@ void __init machine_early_init(const char *cmdline, unsigned int ram,
 				"CPU have it %x\n", msr);
 #endif
 
-	for (src = __ivt_start; src < __ivt_end; src++, dst++)
+	/* Do not copy reset vectors. offset = 0x2 means skip the first
+	 * two instructions. dst is pointer to MB vectors which are placed
+	 * in block ram. If you want to copy reset vector setup offset to 0x0 */
+#if !CONFIG_MANUAL_RESET_VECTOR
+	offset = 0x2;
+#endif
+	dst = (unsigned long *) (offset * sizeof(u32));
+	for (src = __ivt_start + offset; src < __ivt_end; src++, dst++)
 		*dst = *src;
 
 	/* Initialize global data */