From: Tobias Wolf <dev-NTEO@vplace.de>
Subject: [v2] MIPS: Fix memory reservation in bootmem_init for certain non-usermem setups

Commit 67a3ba25aa95 ("MIPS: Fix incorrect mem=X@Y handling") introduced a new
issue for rt288x where "PHYS_OFFSET" is 0x0 but the calculated "ramstart" is
not. As the prerequisite of custom memory map has been removed, this results
in the full memory range of 0x0 - 0x8000000 to be marked as reserved for this
platform.

v2: Correctly compare that usermem is not null.

This patch adds the originally intended prerequisite again.

Signed-off-by: Tobias Wolf <dev-NTEO@vplace.de>
---

--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -285,6 +285,8 @@ static unsigned long __init init_initrd(
  * Initialize the bootmem allocator. It also setup initrd related data
  * if needed.
  */
+static int usermem __initdata;
+
 #if defined(CONFIG_SGI_IP27) || (defined(CONFIG_CPU_LOONGSON3) && defined(CONFIG_NUMA))
 
 static void __init bootmem_init(void)
@@ -323,7 +325,7 @@ static void __init bootmem_init(void)
 	/*
 	 * Reserve any memory between the start of RAM and PHYS_OFFSET
 	 */
-	if (ramstart > PHYS_OFFSET)
+	if (usermem && ramstart > PHYS_OFFSET)
 		memblock_reserve(PHYS_OFFSET, ramstart - PHYS_OFFSET);
 
 	if (PFN_UP(ramstart) > ARCH_PFN_OFFSET) {
@@ -384,8 +386,6 @@ static void __init bootmem_init(void)
 
 #endif	/* CONFIG_SGI_IP27 */
 
-static int usermem __initdata;
-
 static int __init early_parse_mem(char *p)
 {
 	phys_addr_t start, size;