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

[Yunhui Cui]

Implement support for parsing 'memmap' kernel command line parameter.

This patch covers parsing of the following two formats for 'memmap'
parameter values:

- nn[KMG]@ss[KMG]
- nn[KMG]$ss[KMG]

([KMG] = K M or G (kilo, mega, giga))

These two allowed formats for parameter value are already documented
in file kernel-parameters.txt in Documentation/admin-guide folder.
Some architectures already support them, but Mips did not prior to
this patch.

Excerpt from Documentation/admin-guide/kernel-parameters.txt:

memmap=nn[KMG]@ss[KMG]
[KNL] Force usage of a specific region of memory.
Region of memory to be used is from ss to ss+nn.

memmap=nn[KMG]$ss[KMG]
Mark specific memory as reserved.
Region of memory to be reserved is from ss to ss+nn.
Example: Exclude memory from 0x18690000-0x1869ffff
memmap=64K$0x18690000
or
memmap=0x10000$0x18690000

There is no need to update this documentation file with respect to
this patch.

Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
---
 arch/riscv/mm/init.c | 50 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index e3405e4b99af..7be7ec3092ad 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -208,6 +208,56 @@ 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;
+
+	case 0:
+		memblock_reserve(mem_size, -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