1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * memconsole-x86-legacy.c
4 *
5 * EBDA specific parts of the memory based BIOS console.
6 *
7 * Copyright 2017 Google Inc.
8 */
9
10 #include <linux/kernel.h>
11 #include <linux/module.h>
12 #include <linux/dmi.h>
13 #include <linux/mm.h>
14 #include <asm/bios_ebda.h>
15 #include <linux/acpi.h>
16
17 #include "memconsole.h"
18
19 #define BIOS_MEMCONSOLE_V1_MAGIC 0xDEADBABE
20 #define BIOS_MEMCONSOLE_V2_MAGIC (('M')|('C'<<8)|('O'<<16)|('N'<<24))
21
22 struct biosmemcon_ebda {
23 u32 signature;
24 union {
25 struct {
26 u8 enabled;
27 u32 buffer_addr;
28 u16 start;
29 u16 end;
30 u16 num_chars;
31 u8 wrapped;
32 } __packed v1;
33 struct {
34 u32 buffer_addr;
35 /* Misdocumented as number of pages! */
36 u16 num_bytes;
37 u16 start;
38 u16 end;
39 } __packed v2;
40 };
41 } __packed;
42
43 static char *memconsole_baseaddr;
44 static size_t memconsole_length;
45
memconsole_read(char * buf,loff_t pos,size_t count)46 static ssize_t memconsole_read(char *buf, loff_t pos, size_t count)
47 {
48 return memory_read_from_buffer(buf, count, &pos, memconsole_baseaddr,
49 memconsole_length);
50 }
51
found_v1_header(struct biosmemcon_ebda * hdr)52 static void found_v1_header(struct biosmemcon_ebda *hdr)
53 {
54 pr_info("memconsole: BIOS console v1 EBDA structure found at %p\n",
55 hdr);
56 pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num = %d\n",
57 hdr->v1.buffer_addr, hdr->v1.start,
58 hdr->v1.end, hdr->v1.num_chars);
59
60 memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr);
61 memconsole_length = hdr->v1.num_chars;
62 memconsole_setup(memconsole_read);
63 }
64
found_v2_header(struct biosmemcon_ebda * hdr)65 static void found_v2_header(struct biosmemcon_ebda *hdr)
66 {
67 pr_info("memconsole: BIOS console v2 EBDA structure found at %p\n",
68 hdr);
69 pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num_bytes = %d\n",
70 hdr->v2.buffer_addr, hdr->v2.start,
71 hdr->v2.end, hdr->v2.num_bytes);
72
73 memconsole_baseaddr = phys_to_virt(hdr->v2.buffer_addr + hdr->v2.start);
74 memconsole_length = hdr->v2.end - hdr->v2.start;
75 memconsole_setup(memconsole_read);
76 }
77
78 /*
79 * Search through the EBDA for the BIOS Memory Console, and
80 * set the global variables to point to it. Return true if found.
81 */
memconsole_ebda_init(void)82 static bool memconsole_ebda_init(void)
83 {
84 unsigned int address;
85 size_t length, cur;
86
87 address = get_bios_ebda();
88 if (!address) {
89 pr_info("memconsole: BIOS EBDA non-existent.\n");
90 return false;
91 }
92
93 /* EBDA length is byte 0 of EBDA (in KB) */
94 length = *(u8 *)phys_to_virt(address);
95 length <<= 10; /* convert to bytes */
96
97 /*
98 * Search through EBDA for BIOS memory console structure
99 * note: signature is not necessarily dword-aligned
100 */
101 for (cur = 0; cur < length; cur++) {
102 struct biosmemcon_ebda *hdr = phys_to_virt(address + cur);
103
104 /* memconsole v1 */
105 if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) {
106 found_v1_header(hdr);
107 return true;
108 }
109
110 /* memconsole v2 */
111 if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) {
112 found_v2_header(hdr);
113 return true;
114 }
115 }
116
117 pr_info("memconsole: BIOS console EBDA structure not found!\n");
118 return false;
119 }
120
121 static const struct dmi_system_id memconsole_dmi_table[] __initconst = {
122 {
123 .ident = "Google Board",
124 .matches = {
125 DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."),
126 },
127 },
128 {}
129 };
130 MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table);
131
memconsole_find(void)132 static bool __init memconsole_find(void)
133 {
134 if (!dmi_check_system(memconsole_dmi_table))
135 return false;
136
137 return memconsole_ebda_init();
138 }
139
memconsole_x86_init(void)140 static int __init memconsole_x86_init(void)
141 {
142 if (!memconsole_find())
143 return -ENODEV;
144
145 return memconsole_sysfs_init();
146 }
147
memconsole_x86_exit(void)148 static void __exit memconsole_x86_exit(void)
149 {
150 memconsole_exit();
151 }
152
153 module_init(memconsole_x86_init);
154 module_exit(memconsole_x86_exit);
155
156 MODULE_AUTHOR("Google, Inc.");
157 MODULE_DESCRIPTION("EBDA specific parts of the memory based BIOS console.");
158 MODULE_LICENSE("GPL");
159