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 | |
46 | static ssize_t memconsole_read(char *buf, loff_t pos, size_t count) |
47 | { |
48 | return memory_read_from_buffer(to: buf, count, ppos: &pos, from: memconsole_baseaddr, |
49 | available: memconsole_length); |
50 | } |
51 | |
52 | static void (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(address: hdr->v1.buffer_addr); |
61 | memconsole_length = hdr->v1.num_chars; |
62 | memconsole_setup(read_func: memconsole_read); |
63 | } |
64 | |
65 | static void (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(address: hdr->v2.buffer_addr + hdr->v2.start); |
74 | memconsole_length = hdr->v2.end - hdr->v2.start; |
75 | memconsole_setup(read_func: 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 | */ |
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: 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 | |
132 | static bool __init memconsole_find(void) |
133 | { |
134 | if (!dmi_check_system(list: 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" ); |
158 | |