1 /*
2  * memconsole.c
3  *
4  * Infrastructure for importing the BIOS memory based console
5  * into the kernel log ringbuffer.
6  *
7  * Copyright 2010 Google Inc. All rights reserved.
8  */
9 
10 #include <linux/ctype.h>
11 #include <linux/init.h>
12 #include <linux/kernel.h>
13 #include <linux/string.h>
14 #include <linux/sysfs.h>
15 #include <linux/kobject.h>
16 #include <linux/module.h>
17 #include <linux/dmi.h>
18 #include <linux/io.h>
19 #include <asm/bios_ebda.h>
20 
21 #define BIOS_MEMCONSOLE_V1_MAGIC	0xDEADBABE
22 #define BIOS_MEMCONSOLE_V2_MAGIC	(('M')|('C'<<8)|('O'<<16)|('N'<<24))
23 
24 struct biosmemcon_ebda {
25 	u32 signature;
26 	union {
27 		struct {
28 			u8  enabled;
29 			u32 buffer_addr;
30 			u16 start;
31 			u16 end;
32 			u16 num_chars;
33 			u8  wrapped;
34 		} __packed v1;
35 		struct {
36 			u32 buffer_addr;
37 			/* Misdocumented as number of pages! */
38 			u16 num_bytes;
39 			u16 start;
40 			u16 end;
41 		} __packed v2;
42 	};
43 } __packed;
44 
45 static u32 memconsole_baseaddr;
46 static size_t memconsole_length;
47 
48 static ssize_t memconsole_read(struct file *filp, struct kobject *kobp,
49 			       struct bin_attribute *bin_attr, char *buf,
50 			       loff_t pos, size_t count)
51 {
52 	char *memconsole;
53 	ssize_t ret;
54 
55 	memconsole = ioremap_cache(memconsole_baseaddr, memconsole_length);
56 	if (!memconsole) {
57 		pr_err("memconsole: ioremap_cache failed\n");
58 		return -ENOMEM;
59 	}
60 	ret = memory_read_from_buffer(buf, count, &pos, memconsole,
61 				      memconsole_length);
62 	iounmap(memconsole);
63 	return ret;
64 }
65 
66 static struct bin_attribute memconsole_bin_attr = {
67 	.attr = {.name = "log", .mode = 0444},
68 	.read = memconsole_read,
69 };
70 
71 
72 static void __init found_v1_header(struct biosmemcon_ebda *hdr)
73 {
74 	pr_info("BIOS console v1 EBDA structure found at %p\n", hdr);
75 	pr_info("BIOS console buffer at 0x%.8x, "
76 	       "start = %d, end = %d, num = %d\n",
77 	       hdr->v1.buffer_addr, hdr->v1.start,
78 	       hdr->v1.end, hdr->v1.num_chars);
79 
80 	memconsole_length = hdr->v1.num_chars;
81 	memconsole_baseaddr = hdr->v1.buffer_addr;
82 }
83 
84 static void __init found_v2_header(struct biosmemcon_ebda *hdr)
85 {
86 	pr_info("BIOS console v2 EBDA structure found at %p\n", hdr);
87 	pr_info("BIOS console buffer at 0x%.8x, "
88 	       "start = %d, end = %d, num_bytes = %d\n",
89 	       hdr->v2.buffer_addr, hdr->v2.start,
90 	       hdr->v2.end, hdr->v2.num_bytes);
91 
92 	memconsole_length = hdr->v2.end - hdr->v2.start;
93 	memconsole_baseaddr = hdr->v2.buffer_addr + hdr->v2.start;
94 }
95 
96 /*
97  * Search through the EBDA for the BIOS Memory Console, and
98  * set the global variables to point to it.  Return true if found.
99  */
100 static bool __init found_memconsole(void)
101 {
102 	unsigned int address;
103 	size_t length, cur;
104 
105 	address = get_bios_ebda();
106 	if (!address) {
107 		pr_info("BIOS EBDA non-existent.\n");
108 		return false;
109 	}
110 
111 	/* EBDA length is byte 0 of EBDA (in KB) */
112 	length = *(u8 *)phys_to_virt(address);
113 	length <<= 10; /* convert to bytes */
114 
115 	/*
116 	 * Search through EBDA for BIOS memory console structure
117 	 * note: signature is not necessarily dword-aligned
118 	 */
119 	for (cur = 0; cur < length; cur++) {
120 		struct biosmemcon_ebda *hdr = phys_to_virt(address + cur);
121 
122 		/* memconsole v1 */
123 		if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) {
124 			found_v1_header(hdr);
125 			return true;
126 		}
127 
128 		/* memconsole v2 */
129 		if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) {
130 			found_v2_header(hdr);
131 			return true;
132 		}
133 	}
134 
135 	pr_info("BIOS console EBDA structure not found!\n");
136 	return false;
137 }
138 
139 static struct dmi_system_id memconsole_dmi_table[] __initdata = {
140 	{
141 		.ident = "Google Board",
142 		.matches = {
143 			DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."),
144 		},
145 	},
146 	{}
147 };
148 MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table);
149 
150 static int __init memconsole_init(void)
151 {
152 	if (!dmi_check_system(memconsole_dmi_table))
153 		return -ENODEV;
154 
155 	if (!found_memconsole())
156 		return -ENODEV;
157 
158 	memconsole_bin_attr.size = memconsole_length;
159 	return sysfs_create_bin_file(firmware_kobj, &memconsole_bin_attr);
160 }
161 
162 static void __exit memconsole_exit(void)
163 {
164 	sysfs_remove_bin_file(firmware_kobj, &memconsole_bin_attr);
165 }
166 
167 module_init(memconsole_init);
168 module_exit(memconsole_exit);
169 
170 MODULE_AUTHOR("Google, Inc.");
171 MODULE_LICENSE("GPL");
172