memory hotplug: allow setting of phys_device

/sys/devices/system/memory/memoryX/phys_device is supposed to contain the
number of the physical device that the corresponding piece of memory
belongs to.

In case a physical device should be replaced or taken offline for whatever
reason it is necessary to set all corresponding memory pieces offline.
The current implementation always sets phys_device to '0' and there is no
way or hook to change that. Seems like there was a plan to implement that
but it wasn't finished for whatever reason.

So add a weak function which architectures can override to actually set
the phys_device from within add_memory_block().

Signed-off-by: Heiko Carstens <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: Gerald Schaefer <[e-mail]>
Cc: KAMEZAWA Hiroyuki <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/base/memory.c

···
  * differentiation between which *physical* devices each
  * section belongs to...
  */
+int __weak arch_get_memory_phys_device(unsigned long start_pfn)
+{
+	return 0;
+}
 
 static int add_memory_block(int nid, struct mem_section *section,
-			unsigned long state, int phys_device,
-			enum mem_add_context context)
+			unsigned long state, enum mem_add_context context)
 {
 	struct memory_block *mem = kzalloc(sizeof(*mem), GFP_KERNEL);
+	unsigned long start_pfn;
 	int ret = 0;
 
 	if (!mem)
···
 	mem->phys_index = __section_nr(section);
 	mem->state = state;
 	mutex_init(&mem->state_mutex);
-	mem->phys_device = phys_device;
+	start_pfn = section_nr_to_pfn(mem->phys_index);
+	mem->phys_device = arch_get_memory_phys_device(start_pfn);
 
 	ret = register_memory(mem, section);
 	if (!ret)
···
  */
 int register_new_memory(int nid, struct mem_section *section)
 {
-	return add_memory_block(nid, section, MEM_OFFLINE, 0, HOTPLUG);
+	return add_memory_block(nid, section, MEM_OFFLINE, HOTPLUG);
 }
 
 int unregister_memory_section(struct mem_section *section)
···
 		if (!present_section_nr(i))
 			continue;
 		err = add_memory_block(0, __nr_to_section(i), MEM_ONLINE,
-					0, BOOT);
+				       BOOT);
 		if (!ret)
 			ret = err;
 	}

include/linux/memory.h

···
 	struct sys_device sysdev;
 };
 
+int arch_get_memory_phys_device(unsigned long start_pfn);
+
 /* These states are exposed to userspace as text strings in sysfs */
 #define	MEM_ONLINE		(1<<0) /* exposed to userspace */
 #define	MEM_GOING_OFFLINE	(1<<1) /* exposed to userspace */