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d9523678 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
afe9dba4 TE |
2 | /* |
3 | * memconsole-x86-legacy.c | |
4 | * | |
5 | * EBDA specific parts of the memory based BIOS console. | |
6 | * | |
7 | * Copyright 2017 Google Inc. | |
afe9dba4 TE |
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> | |
afe9dba4 TE |
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 | ||
7918cfc4 JW |
43 | static char *memconsole_baseaddr; |
44 | static size_t memconsole_length; | |
45 | ||
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 | ||
afe9dba4 TE |
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 | ||
7918cfc4 JW |
60 | memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr); |
61 | memconsole_length = hdr->v1.num_chars; | |
62 | memconsole_setup(memconsole_read); | |
afe9dba4 TE |
63 | } |
64 | ||
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 | ||
7918cfc4 JW |
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); | |
afe9dba4 TE |
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 | */ | |
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 | ||
6faadbbb | 121 | static const struct dmi_system_id memconsole_dmi_table[] __initconst = { |
afe9dba4 TE |
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 | ||
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 | ||
140 | static int __init memconsole_x86_init(void) | |
141 | { | |
142 | if (!memconsole_find()) | |
143 | return -ENODEV; | |
144 | ||
145 | return memconsole_sysfs_init(); | |
146 | } | |
147 | ||
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_LICENSE("GPL"); |