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 <horms@verge.net.au>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 2d39594..5629e20 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -645,7 +645,7 @@
 	  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
 
@@ -656,6 +656,17 @@
 	  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"
 	depends on PROC_FS