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