[PATCH v2] RISC-V: cmdline: Add support for 'memmap' parameter

[Yunhui Cui]

Add parsing of 'memmap' to use or reserve a specific region of memory.

Implement the following memmap variants:
- memmap=nn[KMG]@ss[KMG]: force usage of a specific region of memory;
- memmap=nn[KMG]$ss[KMG]: mark specified memory as reserved;

Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
---
 arch/riscv/mm/init.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index e3405e4b99af..8e1d93ae5cb2 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -208,6 +208,52 @@ static int __init early_mem(char *p)
 }
 early_param("mem", early_mem);
 
+static void __init parse_memmap_one(char *p)
+{
+	char *oldp;
+	unsigned long start_at, mem_size;
+
+	if (!p)
+		return;
+
+	oldp = p;
+	mem_size = memparse(p, &p);
+	if (p == oldp)
+		return;
+
+	switch (*p) {
+	case '@':
+		start_at = memparse(p + 1, &p);
+		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 void __init setup_bootmem(void)
 {
 	phys_addr_t vmlinux_end = __pa_symbol(&_end);
-- 
2.20.1