[PATCH] [v3] powerpc/4xx: work around CHIP11 errata in a more PAGE_SIZE-friendly way

[Hollis Blanchard <hollisb@us.ibm.com>]

The current CHIP11 errata truncates the device tree memory node, and subtracts
(hardcoded) 4096 bytes. This breaks kernels with larger PAGE_SIZE, since the
bootmem allocator assumes that total memory is a multiple of PAGE_SIZE.

Instead, use a device tree memory reservation to reserve only the 256 bytes
actually affected by the errata, leaving the total memory size unaltered.

Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>

---

Changes from v2:
- David pointed out I'd duplicated the fdt_add_mem_rsv() prototype, and that
  4xx.c should directly include libfdt/libfdt.h instead.

Using large pages results in a huge performance improvement for KVM, and this
patch is required to make Ilya's large page patch work. David and/or Josh,
please apply.

diff --git a/arch/powerpc/boot/4xx.c b/arch/powerpc/boot/4xx.c
--- a/arch/powerpc/boot/4xx.c
+++ b/arch/powerpc/boot/4xx.c
@@ -20,8 +20,9 @@
 #include "ops.h"
 #include "reg.h"
 #include "dcr.h"
+#include "libfdt/libfdt.h"
 
-static unsigned long chip_11_errata(unsigned long memsize)
+static void chip_11_errata(unsigned long memsize)
 {
 	unsigned long pvr;
 
@@ -31,13 +32,11 @@ static unsigned long chip_11_errata(unsi
 		case 0x40000850:
 		case 0x400008d0:
 		case 0x200008d0:
-			memsize -= 4096;
+			fdt_add_mem_rsv(fdt, memsize - 256, 256);
 			break;
 		default:
 			break;
 	}
-
-	return memsize;
 }
 
 /* Read the 4xx SDRAM controller to get size of system memory. */
@@ -53,7 +52,7 @@ void ibm4xx_sdram_fixup_memsize(void)
 			memsize += SDRAM_CONFIG_BANK_SIZE(bank_config);
 	}
 
-	memsize = chip_11_errata(memsize);
+	chip_11_errata(memsize);
 	dt_fixup_memory(0, memsize);
 }
 
@@ -219,7 +218,7 @@ void ibm4xx_denali_fixup_memsize(void)
 		bank = 4; /* 4 banks */
 
 	memsize = cs * (1 << (col+row)) * bank * dpath;
-	memsize = chip_11_errata(memsize);
+	chip_11_errata(memsize);
 	dt_fixup_memory(0, memsize);
 }
 
diff --git a/arch/powerpc/boot/libfdt-wrapper.c b/arch/powerpc/boot/libfdt-wrapper.c
--- a/arch/powerpc/boot/libfdt-wrapper.c
+++ b/arch/powerpc/boot/libfdt-wrapper.c
@@ -51,7 +51,7 @@
 #define devp_offset_find(devp)	(((int)(devp))-1)
 #define devp_offset(devp)	(devp ? ((int)(devp))-1 : 0)
 
-static void *fdt;
+void *fdt;
 static void *buf; /* = NULL */
 
 #define EXPAND_GRANULARITY	1024
diff --git a/arch/powerpc/boot/ops.h b/arch/powerpc/boot/ops.h
--- a/arch/powerpc/boot/ops.h
+++ b/arch/powerpc/boot/ops.h
@@ -14,6 +14,7 @@
 #include <stddef.h>
 #include "types.h"
 #include "string.h"
+#include "libfdt_env.h"
 
 #define	COMMAND_LINE_SIZE	512
 #define	MAX_PATH_LEN		256
@@ -32,6 +33,9 @@ struct platform_ops {
 	void *	(*vmlinux_alloc)(unsigned long size);
 };
 extern struct platform_ops platform_ops;
+
+/* The device tree itself. Should almost always be accessed via dt_ops. */
+extern void *fdt;
 
 /* Device Tree operations */
 struct dt_ops {