[PATCH v4] MIPS: Fix memory reservation in bootmem_init for certain non-usermem setups

[Tobias Wolf <dev-NTEO@vplace.de>]

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.

This patch adds the originally intended prerequisite again.

Signed-off-by: Tobias Wolf <dev-NTEO@vplace.de>
Fixes: 67a3ba25aa95 ("MIPS: Fix incorrect mem=X@Y handling")
Cc: stable@vger.kernel.org # v4.14+
---
 arch/mips/kernel/setup.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 563188ac6fa2..c3ca55128926 100644

v2: Correctly compare that usermem is not null.

v3: Added/changed position of changelog and fixed sender address.

v4: Added "Fixes" and "Cc" tags.
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -371,6 +371,8 @@ static unsigned long __init bootmap_bytes(unsigned long 
pages)
 	return ALIGN(bytes, sizeof(long));
 }
 
+static int usermem __initdata;
+
 static void __init bootmem_init(void)
 {
 	unsigned long reserved_end;
@@ -444,7 +446,7 @@ 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)
 		add_memory_region(PHYS_OFFSET, ramstart - PHYS_OFFSET,
 				  BOOT_MEM_RESERVED);
 
@@ -654,8 +656,6 @@ static void __init bootmem_init(void)
  * initialization hook for anything else was introduced.
  */
 
-static int usermem __initdata;
-
 static int __init early_parse_mem(char *p)
 {
 	phys_addr_t start, size;