memblock: add memblock_start_of_DRAM()

SPARC32 require access to the start address.  Add a new helper
memblock_start_of_DRAM() to give access to the address of the first
memblock - which contains the lowest address.

The awkward name was chosen to match the already present
memblock_end_of_DRAM().

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Yinghai Lu <yinghai@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/memblock.h

@@ -80,6 +80,7 @@ extern phys_addr_t __memblock_alloc_base(phys_addr_t size,
 					   phys_addr_t align,
 					   phys_addr_t max_addr);
 extern phys_addr_t memblock_phys_mem_size(void);
+extern phys_addr_t memblock_start_of_DRAM(void);
 extern phys_addr_t memblock_end_of_DRAM(void);
 extern void memblock_enforce_memory_limit(phys_addr_t memory_limit);
 extern int memblock_is_memory(phys_addr_t addr);

mm/memblock.c

@@ -626,6 +626,12 @@ phys_addr_t __init memblock_phys_mem_size(void)
 	return memblock.memory_size;
 }
 
+/* lowest address */
+phys_addr_t __init_memblock memblock_start_of_DRAM(void)
+{
+	return memblock.memory.regions[0].base;
+}
+
 phys_addr_t __init_memblock memblock_end_of_DRAM(void)
 {
 	int idx = memblock.memory.cnt - 1;