[POWERPC] Add arch-specific walk_memory_remove() for 64-bit powerpc

walk_memory_resource() verifies if there are holes in a given memory
range, by checking against /proc/iomem.  On x86/ia64 system memory is
represented in /proc/iomem.  On powerpc, we don't show system memory as
IO resource in /proc/iomem - instead it's maintained in
/proc/device-tree.

This provides a way for an architecture to provide its own
walk_memory_resource() function.  On powerpc, the memory region is
small (16MB), contiguous and non-overlapping.  So extra checking
against the device-tree is not needed.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Kumar Gala <galak@gate.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/Kconfig

@@ -272,6 +272,9 @@ config HOTPLUG_CPU
 config ARCH_ENABLE_MEMORY_HOTPLUG
 	def_bool y
 
+config ARCH_HAS_WALK_MEMORY
+	def_bool y
+
 config ARCH_ENABLE_MEMORY_HOTREMOVE
 	def_bool y
 

arch/powerpc/mm/mem.c

@@ -145,6 +145,23 @@ int remove_memory(u64 start, u64 size)
 	return ret;
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
+
+/*
+ * walk_memory_resource() needs to make sure there is no holes in a given
+ * memory range. On PPC64, since this range comes from /sysfs, the range
+ * is guaranteed to be valid, non-overlapping and can not contain any
+ * holes. By the time we get here (memory add or remove), /proc/device-tree
+ * is updated and correct. Only reason we need to check against device-tree
+ * would be if we allow user-land to specify a memory range through a
+ * system call/ioctl etc. instead of doing offline/online through /sysfs.
+ */
+int
+walk_memory_resource(unsigned long start_pfn, unsigned long nr_pages, void *arg,
+			int (*func)(unsigned long, unsigned long, void *))
+{
+	return  (*func)(start_pfn, nr_pages, arg);
+}
+
 #endif /* CONFIG_MEMORY_HOTPLUG */
 
 void show_mem(void)

kernel/resource.c

@@ -228,7 +228,7 @@ int release_resource(struct resource *old)
 
 EXPORT_SYMBOL(release_resource);
 
-#ifdef CONFIG_MEMORY_HOTPLUG
+#if defined(CONFIG_MEMORY_HOTPLUG) && !defined(CONFIG_ARCH_HAS_WALK_MEMORY)
 /*
  * Finds the lowest memory reosurce exists within [res->start.res->end)
  * the caller must specify res->start, res->end, res->flags.