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
24struct 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
45static u32 memconsole_baseaddr;
46static size_t memconsole_length;
47
48static 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
66static struct bin_attribute memconsole_bin_attr = {
67	.attr = {.name = "log", .mode = 0444},
68	.read = memconsole_read,
69};
70
71
72static 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
84static 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 */
100static 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
139static 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};
148MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table);
149
150static 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
162static void __exit memconsole_exit(void)
163{
164	sysfs_remove_bin_file(firmware_kobj, &memconsole_bin_attr);
165}
166
167module_init(memconsole_init);
168module_exit(memconsole_exit);
169
170MODULE_AUTHOR("Google, Inc.");
171MODULE_LICENSE("GPL");
172