[PATCH] arm64: mm: add support for memmap kernel parameters

[Barry Song]

memmap should be an useful kernel parameter which has been supported by
x86, mips and xtensa. This patch adds support for ARM64. At this stage,
the below two modes are supported only:
memmap=nn[KMG]@ss[KMG]
Force usage of a specific region of memory

memmap=nn[KMG]$ss[KMG]
Region of memory to be reserved is from ss to ss+nn

If users set memmap=exactmap before memmap=nn[KMG]@ss[KMG], they will
get the exact memory specified by memmap=nn[KMG]@ss[KMG]. For example,
on one machine with 4GB memory, "memmap=exactmap memmap=1G@1G" will
make kernel use the memory from 1GB to 2GB only.

Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
---
 arch/arm64/mm/init.c | 59 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 095540667f0f..f1c6bfdbc953 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -235,6 +235,65 @@ static int __init early_mem(char *p)
 }
 early_param("mem", early_mem);
 
+static int need_remove_real_memblock __initdata;
+
+static void __init parse_memmap_one(char *p)
+{
+	char *oldp;
+	unsigned long start_at, mem_size;
+
+	if (!p)
+		return;
+
+	if (!strncmp(p, "exactmap", 8)) {
+		need_remove_real_memblock = 1;
+		return;
+	}
+
+	oldp = p;
+	mem_size = memparse(p, &p);
+	if (p == oldp)
+		return;
+
+	switch (*p) {
+	case '@':
+		start_at = memparse(p + 1, &p);
+		/*
+		 * use the exactmap defined by nn[KMG]@ss[KMG], remove
+		 * memblock populated by DT etc.
+		 */
+		if (need_remove_real_memblock) {
+			need_remove_real_memblock = 0;
+			memblock_remove(0, ULLONG_MAX);
+		}
+		memblock_add(start_at, mem_size);
+		break;
+	case '$':
+		start_at = memparse(p + 1, &p);
+		memblock_reserve(start_at, mem_size);
+		break;
+	default:
+		pr_warn("Unrecognized memmap syntax: %s\n", p);
+		break;
+	}
+}
+
+static int __init parse_memmap_opt(char *str)
+{
+	while (str) {
+		char *k = strchr(str, ',');
+
+		if (k)
+			*k++ = 0;
+
+		parse_memmap_one(str);
+		str = k;
+	}
+
+	return 0;
+}
+early_param("memmap", parse_memmap_opt);
+
 static int __init early_init_dt_scan_usablemem(unsigned long node,
 		const char *uname, int depth, void *data)
 {
-- 
2.25.1