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 <asm/e820.h> 24 #include <linux/acpi.h> 25 26 #include "memconsole.h" 27 28 #define BIOS_MEMCONSOLE_V1_MAGIC 0xDEADBABE 29 #define BIOS_MEMCONSOLE_V2_MAGIC (('M')|('C'<<8)|('O'<<16)|('N'<<24)) 30 31 struct biosmemcon_ebda { 32 u32 signature; 33 union { 34 struct { 35 u8 enabled; 36 u32 buffer_addr; 37 u16 start; 38 u16 end; 39 u16 num_chars; 40 u8 wrapped; 41 } __packed v1; 42 struct { 43 u32 buffer_addr; 44 /* Misdocumented as number of pages! */ 45 u16 num_bytes; 46 u16 start; 47 u16 end; 48 } __packed v2; 49 }; 50 } __packed; 51 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_setup(phys_to_virt(hdr->v1.buffer_addr), hdr->v1.num_chars); 61 } 62 63 static void found_v2_header(struct biosmemcon_ebda *hdr) 64 { 65 pr_info("memconsole: BIOS console v2 EBDA structure found at %p\n", 66 hdr); 67 pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num_bytes = %d\n", 68 hdr->v2.buffer_addr, hdr->v2.start, 69 hdr->v2.end, hdr->v2.num_bytes); 70 71 memconsole_setup(phys_to_virt(hdr->v2.buffer_addr + hdr->v2.start), 72 hdr->v2.end - hdr->v2.start); 73 } 74 75 /* 76 * Search through the EBDA for the BIOS Memory Console, and 77 * set the global variables to point to it. Return true if found. 78 */ 79 static bool memconsole_ebda_init(void) 80 { 81 unsigned int address; 82 size_t length, cur; 83 84 address = get_bios_ebda(); 85 if (!address) { 86 pr_info("memconsole: BIOS EBDA non-existent.\n"); 87 return false; 88 } 89 90 /* EBDA length is byte 0 of EBDA (in KB) */ 91 length = *(u8 *)phys_to_virt(address); 92 length <<= 10; /* convert to bytes */ 93 94 /* 95 * Search through EBDA for BIOS memory console structure 96 * note: signature is not necessarily dword-aligned 97 */ 98 for (cur = 0; cur < length; cur++) { 99 struct biosmemcon_ebda *hdr = phys_to_virt(address + cur); 100 101 /* memconsole v1 */ 102 if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) { 103 found_v1_header(hdr); 104 return true; 105 } 106 107 /* memconsole v2 */ 108 if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) { 109 found_v2_header(hdr); 110 return true; 111 } 112 } 113 114 pr_info("memconsole: BIOS console EBDA structure not found!\n"); 115 return false; 116 } 117 118 static struct dmi_system_id memconsole_dmi_table[] __initdata = { 119 { 120 .ident = "Google Board", 121 .matches = { 122 DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."), 123 }, 124 }, 125 {} 126 }; 127 MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table); 128 129 static bool __init memconsole_find(void) 130 { 131 if (!dmi_check_system(memconsole_dmi_table)) 132 return false; 133 134 return memconsole_ebda_init(); 135 } 136 137 static int __init memconsole_x86_init(void) 138 { 139 if (!memconsole_find()) 140 return -ENODEV; 141 142 return memconsole_sysfs_init(); 143 } 144 145 static void __exit memconsole_x86_exit(void) 146 { 147 memconsole_exit(); 148 } 149 150 module_init(memconsole_x86_init); 151 module_exit(memconsole_x86_exit); 152 153 MODULE_AUTHOR("Google, Inc."); 154 MODULE_LICENSE("GPL"); 155