MIPS: cmdline: Add support for 'memmap' parameter

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: Miodrag Dinic <[e-mail]>
Signed-off-by: Goran Ferenc <[e-mail]>
Signed-off-by: Aleksandar Markovic <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/16508/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/kernel/setup.c

···
 }
 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;
+
+	if (!strncmp(p, "exactmap", 8)) {
+		pr_err("\"memmap=exactmap\" invalid on MIPS\n");
+		return 0;
+	}
+
+	oldp = p;
+	mem_size = memparse(p, &p);
+	if (p == oldp)
+		return -EINVAL;
+
+	if (*p == '@') {
+		start_at = memparse(p+1, &p);
+		add_memory_region(start_at, mem_size, BOOT_MEM_RAM);
+	} else if (*p == '#') {
+		pr_err("\"memmap=nn#ss\" (force ACPI data) invalid on MIPS\n");
+		return -EINVAL;
+	} else if (*p == '$') {
+		start_at = memparse(p+1, &p);
+		add_memory_region(start_at, mem_size, BOOT_MEM_RESERVED);
+	} else {
+		pr_err("\"memmap\" invalid format!\n");
+		return -EINVAL;
+	}
+
+	if (*p == '\0') {
+		usermem = 1;
+		return 0;
+	} else
+		return -EINVAL;
+}
+early_param("memmap", early_parse_memmap);
+
 #ifdef CONFIG_PROC_VMCORE
 unsigned long setup_elfcorehdr, setup_elfcorehdr_size;
 static int __init early_parse_elfcorehdr(char *p)