sh: kexec: Add PHYSICAL_START

Add PHYSICAL_START kernel configuration parameter to set the address at
which the kernel should be loaded.

It has been observed on an sh7757lcr that simply modifying MEMORY_START
does not achieve this goal for 32bit sh. This is due to MEMORY_OFFSET in
arch/sh/kernel/vmlinux.lds.S bot being based on MEMORY_START on such
systems.

Signed-off-by: Simon Horman <[e-mail]>
Signed-off-by: Paul Mundt <[e-mail]>

arch/sh/Kconfig

···
 	  a specially reserved region and then later executed after
 	  a crash by kdump/kexec. The crash dump kernel must be compiled
 	  to a memory address not used by the main kernel using
-	  MEMORY_START.
+	  PHYSICAL_START.
 
 	  For more details see Documentation/kdump/kdump.txt
 
···
 	help
 	  Jump between original kernel and kexeced kernel and invoke
 	  code via KEXEC
+
+config PHYSICAL_START
+	hex "Physical address where the kernel is loaded" if (EXPERT || CRASH_DUMP)
+	default MEMORY_START
+	---help---
+	  This gives the physical address where the kernel is loaded
+	  and is ordinarily the same as MEMORY_START.
+
+	  Different values are primarily used in the case of kexec on panic
+	  where the fail safe kernel needs to run at a different address
+	  than the panic-ed kernel.
 
 config SECCOMP
 	bool "Enable seccomp to safely compute untrusted bytecode"

arch/sh/boot/Makefile

···
 CONFIG_BOOT_LINK_OFFSET	?= 0x00800000
 CONFIG_ZERO_PAGE_OFFSET	?= 0x00001000
 CONFIG_ENTRY_OFFSET	?= 0x00001000
+CONFIG_PHYSICAL_START	?= $(CONFIG_MEMORY_START)
 
 suffix-y := bin
 suffix-$(CONFIG_KERNEL_GZIP)	:= gz
···
 	$(Q)$(MAKE) $(build)=$(obj)/romimage $@
 
 KERNEL_MEMORY	:= $(shell /bin/bash -c 'printf "0x%08x" \
-		     $$[$(CONFIG_MEMORY_START) & 0x1fffffff]')
+		     $$[$(CONFIG_PHYSICAL_START) & 0x1fffffff]')
 
 KERNEL_LOAD	:= $(shell /bin/bash -c 'printf "0x%08x" \
 		     $$[$(CONFIG_PAGE_OFFSET)  + \
···
 	@echo '  Image $@ is ready'
 
 export CONFIG_PAGE_OFFSET CONFIG_MEMORY_START CONFIG_BOOT_LINK_OFFSET \
-       CONFIG_ZERO_PAGE_OFFSET CONFIG_ENTRY_OFFSET KERNEL_MEMORY suffix-y
+       CONFIG_PHYSICAL_START CONFIG_ZERO_PAGE_OFFSET CONFIG_ENTRY_OFFSET \
+       KERNEL_MEMORY suffix-y

arch/sh/include/asm/page.h

···
 #define __MEMORY_SIZE		CONFIG_MEMORY_SIZE
 
 /*
+ * PHYSICAL_OFFSET is the offset in physical memory where the base
+ * of the kernel is loaded.
+ */
+#ifdef CONFIG_PHYSICAL_START
+#define PHYSICAL_OFFSET (CONFIG_PHYSICAL_START - __MEMORY_START)
+#else
+#define PHYSICAL_OFFSET 0
+#endif
+
+/*
  * PAGE_OFFSET is the virtual address of the start of kernel address
  * space.
  */

arch/sh/kernel/vmlinux.lds.S

···
 ENTRY(_start)
 SECTIONS
 {
-	. = PAGE_OFFSET + MEMORY_OFFSET + CONFIG_ZERO_PAGE_OFFSET;
+	. = PAGE_OFFSET + MEMORY_OFFSET + PHYSICAL_OFFSET + CONFIG_ZERO_PAGE_OFFSET;
 
 	_text = .;		/* Text and read-only data */
 

arch/sh/mm/init.c

···
 static void __init early_reserve_mem(void)
 {
 	unsigned long start_pfn;
+	u32 zero_base = (u32)__MEMORY_START + (u32)PHYSICAL_OFFSET;
+	u32 start = zero_base + (u32)CONFIG_ZERO_PAGE_OFFSET;
 
 	/*
 	 * Partially used pages are not usable - thus
···
 	 * this catches the (definitely buggy) case of us accidentally
 	 * initializing the bootmem allocator with an invalid RAM area.
 	 */
-	memblock_reserve(__MEMORY_START + CONFIG_ZERO_PAGE_OFFSET,
-		    (PFN_PHYS(start_pfn) + PAGE_SIZE - 1) -
-		    (__MEMORY_START + CONFIG_ZERO_PAGE_OFFSET));
+	memblock_reserve(start, (PFN_PHYS(start_pfn) + PAGE_SIZE - 1) - start);
 
 	/*
 	 * Reserve physical pages below CONFIG_ZERO_PAGE_OFFSET.
 	 */
 	if (CONFIG_ZERO_PAGE_OFFSET != 0)
-		memblock_reserve(__MEMORY_START, CONFIG_ZERO_PAGE_OFFSET);
+		memblock_reserve(zero_base, CONFIG_ZERO_PAGE_OFFSET);
 
 	/*
 	 * Handle additional early reservations