On the Cirrus Logic ep93xx, system RAM isn't one nice physically
contiguous region as it is on most SoCs, but it is spread out over
between one and four memory banks.

What's worse, RAM doesn't necessarily start at any fixed physical
memory location.  The start of RAM (PHYS_OFFSET) is not only board-
specific, but on some boards also depends on jumper settings (whether
async or sync boot mode is selected.)

The attached patch adds the RUNTIME_PHYS_OFFSET config option, which,
if selected, turns PHYS_OFFSET into a variable which is determined and
set by __create_page_tables by looking at the current pc.  This allows
booting a single kernel image on all the different flavors of ep93xx
boards, reducing user confusion and hopefully pleasing our kautobuild
admin :-)  If the option isn't selected, there's zero impact.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
===================================================================
20070202 modified to apply cleanly to linux-2.6.20-rc7 - NZG
===================================================================
diff -Naur linux-2.6.20-rc7/arch/arm/Kconfig linux-2.6.20-rc7-e1.0/arch/arm/Kconfig
--- linux-2.6.20-rc7/arch/arm/Kconfig	2007-02-02 10:26:21.000000000 -0600
+++ linux-2.6.20-rc7-e1.0/arch/arm/Kconfig	2007-02-02 16:23:05.000000000 -0600
@@ -113,6 +113,9 @@
 	help
 	  The base address of exception vectors.
 
+config RUNTIME_PHYS_OFFSET
+	bool
+
 source "init/Kconfig"
 
 menu "System Type"
@@ -187,6 +190,7 @@
 	bool "EP93xx-based"
 	select ARM_AMBA
 	select ARM_VIC
+	select RUNTIME_PHYS_OFFSET
 	help
 	  This enables support for the Cirrus EP93xx series of CPUs.
 
diff -Naur linux-2.6.20-rc7/arch/arm/boot/compressed/Makefile linux-2.6.20-rc7-e1.0/arch/arm/boot/compressed/Makefile
--- linux-2.6.20-rc7/arch/arm/boot/compressed/Makefile	2006-11-29 15:57:37.000000000 -0600
+++ linux-2.6.20-rc7-e1.0/arch/arm/boot/compressed/Makefile	2007-02-02 16:23:05.000000000 -0600
@@ -78,13 +78,10 @@
 EXTRA_CFLAGS  := -fpic
 EXTRA_AFLAGS  :=
 
-# Supply ZRELADDR, INITRD_PHYS and PARAMS_PHYS to the decompressor via
-# linker symbols.  We only define initrd_phys and params_phys if the
-# machine class defined the corresponding makefile variable.
+# Supply ZRELADDR and PARAMS_PHYS to the decompressor via linker
+# symbols.  We only define params_phys if the machine class defined
+# the corresponding makefile variable.
 LDFLAGS_vmlinux := --defsym zreladdr=$(ZRELADDR)
-ifneq ($(INITRD_PHYS),)
-LDFLAGS_vmlinux += --defsym initrd_phys=$(INITRD_PHYS)
-endif
 ifneq ($(PARAMS_PHYS),)
 LDFLAGS_vmlinux += --defsym params_phys=$(PARAMS_PHYS)
 endif
diff -Naur linux-2.6.20-rc7/arch/arm/boot/compressed/head.S linux-2.6.20-rc7-e1.0/arch/arm/boot/compressed/head.S
--- linux-2.6.20-rc7/arch/arm/boot/compressed/head.S	2006-11-29 15:57:37.000000000 -0600
+++ linux-2.6.20-rc7-e1.0/arch/arm/boot/compressed/head.S	2007-02-02 16:23:05.000000000 -0600
@@ -156,6 +156,11 @@
 		.text
 		adr	r0, LC0
 		ldmia	r0, {r1, r2, r3, r4, r5, r6, ip, sp}
+#ifdef CONFIG_RUNTIME_PHYS_OFFSET
+		and	r10, pc, #0xf0000000	@ fix up zreladdr
+		add	r4, r4, r10
+#endif
+
 		subs	r0, r0, r1		@ calculate the delta offset
 
 						@ if delta is zero, we are
diff -Naur linux-2.6.20-rc7/arch/arm/kernel/head.S linux-2.6.20-rc7-e1.0/arch/arm/kernel/head.S
--- linux-2.6.20-rc7/arch/arm/kernel/head.S	2007-02-02 10:26:21.000000000 -0600
+++ linux-2.6.20-rc7-e1.0/arch/arm/kernel/head.S	2007-02-02 16:36:21.000000000 -0600
@@ -43,8 +43,8 @@
 	.globl	swapper_pg_dir
 	.equ	swapper_pg_dir, KERNEL_RAM_VADDR - 0x4000
 
-	.macro	pgtbl, rd
-	ldr	\rd, =(KERNEL_RAM_PADDR - 0x4000)
+	.macro	pgtbl, rd, phys_offset
+	add	\rd, \phys_offset, #(TEXT_OFFSET - 0x4000)
 	.endm
 
 #ifdef CONFIG_XIP_KERNEL
@@ -206,10 +206,22 @@
  * Returns:
  *  r0, r3, r6, r7 corrupted
  *  r4 = physical page table address
+ *  r5 = PHYS_OFFSET
  */
 	.type	__create_page_tables, %function
 __create_page_tables:
-	pgtbl	r4				@ page table address
+#ifdef CONFIG_RUNTIME_PHYS_OFFSET
+	adr	r5, stext
+	sub	r5, r5, #TEXT_OFFSET		@ r5 = phys_offset
+
+	ldr	r4, =(phys_offset - PAGE_OFFSET)
+	add	r4, r4, r5
+	str	r5, [r4]			@ save phys_offset
+#else
+	mov	r5, #PHYS_OFFSET		@ r5 = phys_offset
+#endif
+
+	pgtbl	r4, r5				@ r4 = page table address
 
 	/*
 	 * Clear the 16K level 1 swapper page table
@@ -255,8 +267,7 @@
 	 * Then map first 1MB of ram in case it contains our boot params.
 	 */
 	add	r0, r4, #PAGE_OFFSET >> 18
-	orr	r6, r7, #(PHYS_OFFSET & 0xff000000)
-	orr	r6, r6, #(PHYS_OFFSET & 0x00e00000)
+	orr	r6, r7, r5
 	str	r6, [r0]
 
 #ifdef CONFIG_XIP_KERNEL
diff -Naur linux-2.6.20-rc7/arch/arm/kernel/setup.c linux-2.6.20-rc7-e1.0/arch/arm/kernel/setup.c
--- linux-2.6.20-rc7/arch/arm/kernel/setup.c	2007-02-02 10:26:21.000000000 -0600
+++ linux-2.6.20-rc7-e1.0/arch/arm/kernel/setup.c	2007-02-02 16:23:05.000000000 -0600
@@ -59,6 +59,16 @@
 extern int root_mountflags;
 extern void _stext, _text, _etext, __data_start, _edata, _end;
 
+#ifdef CONFIG_RUNTIME_PHYS_OFFSET
+/*
+ * The assignment is here solely to prevent this variable from ending
+ * up in bss.  As the early startup code writes to it, we don't want it
+ * to be zeroed again later.
+ */
+unsigned long phys_offset = 0xdeadbeef;
+EXPORT_SYMBOL(phys_offset);
+#endif
+
 unsigned int processor_id;
 unsigned int __machine_arch_type;
 EXPORT_SYMBOL(__machine_arch_type);
@@ -749,7 +759,7 @@
 	{ tag_size(tag_core), ATAG_CORE },
 	{ 1, PAGE_SIZE, 0xff },
 	{ tag_size(tag_mem32), ATAG_MEM },
-	{ MEM_SIZE, PHYS_OFFSET },
+	{ MEM_SIZE, 0 },
 	{ 0, ATAG_NONE }
 };
 
@@ -770,6 +780,8 @@
 	struct machine_desc *mdesc;
 	char *from = default_command_line;
 
+	init_tags.mem.start = PHYS_OFFSET;
+
 	setup_processor();
 	mdesc = setup_machine(machine_arch_type);
 	machine_name = mdesc->name;
diff -Naur linux-2.6.20-rc7/arch/arm/mach-ep93xx/Makefile.boot linux-2.6.20-rc7-e1.0/arch/arm/mach-ep93xx/Makefile.boot
--- linux-2.6.20-rc7/arch/arm/mach-ep93xx/Makefile.boot	2006-11-29 15:57:37.000000000 -0600
+++ linux-2.6.20-rc7-e1.0/arch/arm/mach-ep93xx/Makefile.boot	2007-02-02 16:23:05.000000000 -0600
@@ -1,2 +1 @@
    zreladdr-y	:= 0x00008000
-params_phys-y	:= 0x00000100
diff -Naur linux-2.6.20-rc7/include/asm-arm/arch-ep93xx/memory.h linux-2.6.20-rc7-e1.0/include/asm-arm/arch-ep93xx/memory.h
--- linux-2.6.20-rc7/include/asm-arm/arch-ep93xx/memory.h	2006-11-29 15:57:37.000000000 -0600
+++ linux-2.6.20-rc7-e1.0/include/asm-arm/arch-ep93xx/memory.h	2007-02-02 16:23:05.000000000 -0600
@@ -5,7 +5,9 @@
 #ifndef __ASM_ARCH_MEMORY_H
 #define __ASM_ARCH_MEMORY_H
 
+#ifndef CONFIG_RUNTIME_PHYS_OFFSET
 #define PHYS_OFFSET		UL(0x00000000)
+#endif
 
 #define __bus_to_virt(x)	__phys_to_virt(x)
 #define __virt_to_bus(x)	__virt_to_phys(x)
diff -Naur linux-2.6.20-rc7/include/asm-arm/memory.h linux-2.6.20-rc7-e1.0/include/asm-arm/memory.h
--- linux-2.6.20-rc7/include/asm-arm/memory.h	2007-02-02 10:26:27.000000000 -0600
+++ linux-2.6.20-rc7-e1.0/include/asm-arm/memory.h	2007-02-02 16:23:05.000000000 -0600
@@ -73,6 +73,14 @@
  */
 #define IOREMAP_MAX_ORDER	24
 
+/*
+ * PHYS_OFFSET determined at run time?
+ */
+#if defined(CONFIG_RUNTIME_PHYS_OFFSET) && !defined(__ASSEMBLY__)
+extern unsigned long phys_offset;
+#define PHYS_OFFSET		(phys_offset)
+#endif
+
 #else /* CONFIG_MMU */
 
 /*