[PATCH v4 3/4] MIPS: Refactor early_parse_memmap() to fix memmap= parameter

[Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>]

According to Documentation/admin-guide/kernel-parameters.txt,
the kernel command-line parameter memmap= means "Force usage
of a specific region of memory", but when add "memmap=3G@64M"
to the command-line, kernel boot hangs in sparse_init().

In order to support memmap=limit@base, refactor the function
early_parse_memmap() and then use memblock_mem_range_remove_map()
to limit the memory region.

With this patch, when add "memmap=3G@64M" to the command-line,
the kernel boots successfully, we can see the following messages:

  [    0.000000] Memory limited to 64MB-3136MB
  ...
  [    0.000000] Early memory node ranges
  [    0.000000]   node   0: [mem 0x0000000004000000-0x000000000effffff]
  [    0.000000]   node   0: [mem 0x0000000090200000-0x00000000ffffffff]
  [    0.000000]   node   0: [mem 0x0000000120000000-0x00000001653fffff]
  ...
  [    0.000000] Memory: 3070816K/3147776K available (...)

When add "memmap=128M@64M nr_cpus=1 init 3" to the command-line,
the kernel also boots successfully, we can see the following messages:

  [    0.000000] Memory limited to 64MB-192MB
  ...
  [    0.000000] Early memory node ranges
  [    0.000000]   node   0: [mem 0x0000000004000000-0x000000000c1fffff]
  ...
  [    0.000000] Memory: 95312K/133120K available (...)

After login, the output of free command is consistent with the
above log.

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---
 arch/mips/kernel/setup.c | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 50396ba..30c7d95 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -340,6 +340,7 @@ static void __init bootmem_init(void)
 
 static int usermem __initdata;
 static phys_addr_t memory_limit;
+static phys_addr_t memory_base;
 
 static int __init early_parse_mem(char *p)
 {
@@ -356,7 +357,6 @@ early_param("mem", early_parse_mem);
 static int __init early_parse_memmap(char *p)
 {
 	char *oldp;
-	u64 start_at, mem_size;
 
 	if (!p)
 		return -EINVAL;
@@ -367,30 +367,38 @@ static int __init early_parse_memmap(char *p)
 	}
 
 	oldp = p;
-	mem_size = memparse(p, &p);
+	memory_limit = memparse(p, &p) & PAGE_MASK;
 	if (p == oldp)
 		return -EINVAL;
 
 	if (*p == '@') {
-		start_at = memparse(p+1, &p);
-		memblock_add(start_at, mem_size);
+		memory_base = memparse(p + 1, &p) & PAGE_MASK;
+	} else if (*p == '$') {
+		memory_base = memparse(p+1, &p) & PAGE_MASK;
+		memblock_reserve(memory_base, memory_limit);
+		pr_notice("Memory reserved to %lluMB-%lluMB\n",
+			  (u64)memory_base >> 20, (u64)(memory_base + memory_limit) >> 20);
+		memory_base = 0;
+		memory_limit = 0;
+		return 0;
 	} else if (*p == '#') {
-		pr_err("\"memmap=nn#ss\" (force ACPI data) invalid on MIPS\n");
+		pr_err("\"memmap=nn#ss\" invalid on MIPS\n");
+		memory_limit = 0;
+		return -EINVAL;
+	} else if (*p == '!') {
+		pr_err("\"memmap=nn!ss\" invalid on MIPS\n");
+		memory_limit = 0;
 		return -EINVAL;
-	} else if (*p == '$') {
-		start_at = memparse(p+1, &p);
-		memblock_add(start_at, mem_size);
-		memblock_reserve(start_at, mem_size);
 	} else {
-		pr_err("\"memmap\" invalid format!\n");
+		pr_err("Unrecognized memmap syntax: %s\n", p);
+		memory_limit = 0;
 		return -EINVAL;
 	}
 
-	if (*p == '\0') {
-		usermem = 1;
-		return 0;
-	} else
-		return -EINVAL;
+	pr_notice("Memory limited to %lluMB-%lluMB\n",
+		  (u64)memory_base >> 20, (u64)(memory_base + memory_limit) >> 20);
+
+	return *p == '\0' ? 0 : -EINVAL;
 }
 early_param("memmap", early_parse_memmap);
 
@@ -667,7 +675,7 @@ static void __init arch_mem_init(char **cmdline_p)
 		__pa_symbol(&__nosave_end) - __pa_symbol(&__nosave_begin));
 
 	/* Limit the memory. */
-	memblock_enforce_memory_limit(memory_limit);
+	memblock_mem_range_remove_map(memory_base, memory_limit);
 	memblock_allow_resize();
 
 	early_memtest(PFN_PHYS(ARCH_PFN_OFFSET), PFN_PHYS(max_low_pfn));
-- 
2.1.0