1 /*
2  * memconsole-x86-legacy.c
3  *
4  * EBDA specific parts of the memory based BIOS console.
5  *
6  * Copyright 2017 Google Inc.
7  *
8  * This program is free software; you can redistribute it and/or modify
9  * it under the terms of the GNU General Public License v2.0 as published by
10  * the Free Software Foundation.
11  *
12  * This program is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15  * GNU General Public License for more details.
16  */
17 
18 #include <linux/kernel.h>
19 #include <linux/module.h>
20 #include <linux/dmi.h>
21 #include <linux/mm.h>
22 #include <asm/bios_ebda.h>
23 #include <linux/acpi.h>
24 
25 #include "memconsole.h"
26 
27 #define BIOS_MEMCONSOLE_V1_MAGIC	0xDEADBABE
28 #define BIOS_MEMCONSOLE_V2_MAGIC	(('M')|('C'<<8)|('O'<<16)|('N'<<24))
29 
30 struct biosmemcon_ebda {
31 	u32 signature;
32 	union {
33 		struct {
34 			u8  enabled;
35 			u32 buffer_addr;
36 			u16 start;
37 			u16 end;
38 			u16 num_chars;
39 			u8  wrapped;
40 		} __packed v1;
41 		struct {
42 			u32 buffer_addr;
43 			/* Misdocumented as number of pages! */
44 			u16 num_bytes;
45 			u16 start;
46 			u16 end;
47 		} __packed v2;
48 	};
49 } __packed;
50 
51 static char *memconsole_baseaddr;
52 static size_t memconsole_length;
53 
54 static ssize_t memconsole_read(char *buf, loff_t pos, size_t count)
55 {
56 	return memory_read_from_buffer(buf, count, &pos, memconsole_baseaddr,
57 				       memconsole_length);
58 }
59 
60 static void found_v1_header(struct biosmemcon_ebda *hdr)
61 {
62 	pr_info("memconsole: BIOS console v1 EBDA structure found at %p\n",
63 		hdr);
64 	pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num = %d\n",
65 		hdr->v1.buffer_addr, hdr->v1.start,
66 		hdr->v1.end, hdr->v1.num_chars);
67 
68 	memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr);
69 	memconsole_length = hdr->v1.num_chars;
70 	memconsole_setup(memconsole_read);
71 }
72 
73 static void found_v2_header(struct biosmemcon_ebda *hdr)
74 {
75 	pr_info("memconsole: BIOS console v2 EBDA structure found at %p\n",
76 		hdr);
77 	pr_info("memconsole: BIOS console buffer at 0x%.8x, 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_baseaddr = phys_to_virt(hdr->v2.buffer_addr + hdr->v2.start);
82 	memconsole_length = hdr->v2.end - hdr->v2.start;
83 	memconsole_setup(memconsole_read);
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 memconsole_ebda_init(void)
91 {
92 	unsigned int address;
93 	size_t length, cur;
94 
95 	address = get_bios_ebda();
96 	if (!address) {
97 		pr_info("memconsole: 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 	pr_info("memconsole: BIOS console EBDA structure not found!\n");
126 	return false;
127 }
128 
129 static const struct dmi_system_id memconsole_dmi_table[] __initconst = {
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 bool __init memconsole_find(void)
141 {
142 	if (!dmi_check_system(memconsole_dmi_table))
143 		return false;
144 
145 	return memconsole_ebda_init();
146 }
147 
148 static int __init memconsole_x86_init(void)
149 {
150 	if (!memconsole_find())
151 		return -ENODEV;
152 
153 	return memconsole_sysfs_init();
154 }
155 
156 static void __exit memconsole_x86_exit(void)
157 {
158 	memconsole_exit();
159 }
160 
161 module_init(memconsole_x86_init);
162 module_exit(memconsole_x86_exit);
163 
164 MODULE_AUTHOR("Google, Inc.");
165 MODULE_LICENSE("GPL");
166