2 * memconsole-x86-legacy.c
4 * EBDA specific parts of the memory based BIOS console.
6 * Copyright 2017 Google Inc.
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.
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.
18 #include <linux/kernel.h>
19 #include <linux/module.h>
20 #include <linux/dmi.h>
22 #include <asm/bios_ebda.h>
23 #include <linux/acpi.h>
25 #include "memconsole.h"
27 #define BIOS_MEMCONSOLE_V1_MAGIC 0xDEADBABE
28 #define BIOS_MEMCONSOLE_V2_MAGIC (('M')|('C'<<8)|('O'<<16)|('N'<<24))
30 struct biosmemcon_ebda {
43 /* Misdocumented as number of pages! */
51 static void found_v1_header(struct biosmemcon_ebda *hdr)
53 pr_info("memconsole: BIOS console v1 EBDA structure found at %p\n",
55 pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num = %d\n",
56 hdr->v1.buffer_addr, hdr->v1.start,
57 hdr->v1.end, hdr->v1.num_chars);
59 memconsole_setup(phys_to_virt(hdr->v1.buffer_addr), hdr->v1.num_chars);
62 static void found_v2_header(struct biosmemcon_ebda *hdr)
64 pr_info("memconsole: BIOS console v2 EBDA structure found at %p\n",
66 pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num_bytes = %d\n",
67 hdr->v2.buffer_addr, hdr->v2.start,
68 hdr->v2.end, hdr->v2.num_bytes);
70 memconsole_setup(phys_to_virt(hdr->v2.buffer_addr + hdr->v2.start),
71 hdr->v2.end - hdr->v2.start);
75 * Search through the EBDA for the BIOS Memory Console, and
76 * set the global variables to point to it. Return true if found.
78 static bool memconsole_ebda_init(void)
83 address = get_bios_ebda();
85 pr_info("memconsole: BIOS EBDA non-existent.\n");
89 /* EBDA length is byte 0 of EBDA (in KB) */
90 length = *(u8 *)phys_to_virt(address);
91 length <<= 10; /* convert to bytes */
94 * Search through EBDA for BIOS memory console structure
95 * note: signature is not necessarily dword-aligned
97 for (cur = 0; cur < length; cur++) {
98 struct biosmemcon_ebda *hdr = phys_to_virt(address + cur);
101 if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) {
102 found_v1_header(hdr);
107 if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) {
108 found_v2_header(hdr);
113 pr_info("memconsole: BIOS console EBDA structure not found!\n");
117 static struct dmi_system_id memconsole_dmi_table[] __initdata = {
119 .ident = "Google Board",
121 DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."),
126 MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table);
128 static bool __init memconsole_find(void)
130 if (!dmi_check_system(memconsole_dmi_table))
133 return memconsole_ebda_init();
136 static int __init memconsole_x86_init(void)
138 if (!memconsole_find())
141 return memconsole_sysfs_init();
144 static void __exit memconsole_x86_exit(void)
149 module_init(memconsole_x86_init);
150 module_exit(memconsole_x86_exit);
152 MODULE_AUTHOR("Google, Inc.");
153 MODULE_LICENSE("GPL");