[PATCH] powerpc: Add CONFIG_CRASH_DUMP

This patch adds a Kconfig variable, CONFIG_CRASH_DUMP, which configures the
built kernel for use as a Kdump kernel.

Currently "all" this involves is changing the value of KERNELBASE to 32 MB.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/Kconfig

@@ -379,6 +379,17 @@ config CELL_IIC
 	bool
 	default y
 
+config CRASH_DUMP
+	bool "kernel crash dumps (EXPERIMENTAL)"
+	depends on PPC_MULTIPLATFORM
+	depends on EXPERIMENTAL
+	help
+	  Build a kernel suitable for use as a kdump capture kernel.
+	  The kernel will be linked at a different address than normal, and
+	  so can only be used for Kdump.
+
+	  Don't change this unless you know what you are doing.
+
 config IBMVIO
 	depends on PPC_PSERIES || PPC_ISERIES
 	bool

arch/powerpc/kernel/setup_64.c

@@ -512,6 +512,9 @@ void __init setup_system(void)
 	       ppc64_caches.iline_size);
 	printk("htab_address                  = 0x%p\n", htab_address);
 	printk("htab_hash_mask                = 0x%lx\n", htab_hash_mask);
+#if PHYSICAL_START > 0
+	printk("physical_start                = 0x%x\n", PHYSICAL_START);
+#endif
 	printk("-----------------------------------------------------\n");
 
 	mm_init_ppc64();

include/asm-powerpc/page.h

@@ -51,8 +51,16 @@
  *
  * If you want to test if something's a kernel address, use is_kernel_addr().
  */
+
+#ifdef CONFIG_CRASH_DUMP
+/* Kdump kernel runs at 32 MB, change at your peril. */
+#define PHYSICAL_START	0x2000000
+#else
+#define PHYSICAL_START	0x0
+#endif
+
 #define PAGE_OFFSET     ASM_CONST(CONFIG_KERNEL_START)
-#define KERNELBASE      PAGE_OFFSET
+#define KERNELBASE      (PAGE_OFFSET + PHYSICAL_START)
 
 #ifdef CONFIG_DISCONTIGMEM
 #define page_to_pfn(page)	discontigmem_page_to_pfn(page)