1 /* 2 * memconsole.c 3 * 4 * Infrastructure for importing the BIOS memory based console 5 * into the kernel log ringbuffer. 6 * 7 * Copyright 2010 Google Inc. All rights reserved. 8 */ 9 10 #include <linux/ctype.h> 11 #include <linux/init.h> 12 #include <linux/kernel.h> 13 #include <linux/string.h> 14 #include <linux/sysfs.h> 15 #include <linux/kobject.h> 16 #include <linux/module.h> 17 #include <linux/dmi.h> 18 #include <asm/bios_ebda.h> 19 20 #define BIOS_MEMCONSOLE_V1_MAGIC 0xDEADBABE 21 #define BIOS_MEMCONSOLE_V2_MAGIC (('M')|('C'<<8)|('O'<<16)|('N'<<24)) 22 23 struct biosmemcon_ebda { 24 u32 signature; 25 union { 26 struct { 27 u8 enabled; 28 u32 buffer_addr; 29 u16 start; 30 u16 end; 31 u16 num_chars; 32 u8 wrapped; 33 } __packed v1; 34 struct { 35 u32 buffer_addr; 36 /* Misdocumented as number of pages! */ 37 u16 num_bytes; 38 u16 start; 39 u16 end; 40 } __packed v2; 41 }; 42 } __packed; 43 44 static char *memconsole_baseaddr; 45 static size_t memconsole_length; 46 47 static ssize_t memconsole_read(struct file *filp, struct kobject *kobp, 48 struct bin_attribute *bin_attr, char *buf, 49 loff_t pos, size_t count) 50 { 51 return memory_read_from_buffer(buf, count, &pos, memconsole_baseaddr, 52 memconsole_length); 53 } 54 55 static struct bin_attribute memconsole_bin_attr = { 56 .attr = {.name = "log", .mode = 0444}, 57 .read = memconsole_read, 58 }; 59 60 61 static void found_v1_header(struct biosmemcon_ebda *hdr) 62 { 63 printk(KERN_INFO "BIOS console v1 EBDA structure found at %p\n", hdr); 64 printk(KERN_INFO "BIOS console buffer at 0x%.8x, " 65 "start = %d, end = %d, num = %d\n", 66 hdr->v1.buffer_addr, hdr->v1.start, 67 hdr->v1.end, hdr->v1.num_chars); 68 69 memconsole_length = hdr->v1.num_chars; 70 memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr); 71 } 72 73 static void found_v2_header(struct biosmemcon_ebda *hdr) 74 { 75 printk(KERN_INFO "BIOS console v2 EBDA structure found at %p\n", hdr); 76 printk(KERN_INFO "BIOS console buffer at 0x%.8x, " 77 "start = %d, end = %d, num_bytes = %d\n", 78 hdr->v2.buffer_addr, hdr->v2.start, 79 hdr->v2.end, hdr->v2.num_bytes); 80 81 memconsole_length = hdr->v2.end - hdr->v2.start; 82 memconsole_baseaddr = phys_to_virt(hdr->v2.buffer_addr 83 + hdr->v2.start); 84 } 85 86 /* 87 * Search through the EBDA for the BIOS Memory Console, and 88 * set the global variables to point to it. Return true if found. 89 */ 90 static bool found_memconsole(void) 91 { 92 unsigned int address; 93 size_t length, cur; 94 95 address = get_bios_ebda(); 96 if (!address) { 97 printk(KERN_INFO "BIOS EBDA non-existent.\n"); 98 return false; 99 } 100 101 /* EBDA length is byte 0 of EBDA (in KB) */ 102 length = *(u8 *)phys_to_virt(address); 103 length <<= 10; /* convert to bytes */ 104 105 /* 106 * Search through EBDA for BIOS memory console structure 107 * note: signature is not necessarily dword-aligned 108 */ 109 for (cur = 0; cur < length; cur++) { 110 struct biosmemcon_ebda *hdr = phys_to_virt(address + cur); 111 112 /* memconsole v1 */ 113 if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) { 114 found_v1_header(hdr); 115 return true; 116 } 117 118 /* memconsole v2 */ 119 if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) { 120 found_v2_header(hdr); 121 return true; 122 } 123 } 124 125 printk(KERN_INFO "BIOS console EBDA structure not found!\n"); 126 return false; 127 } 128 129 static struct dmi_system_id memconsole_dmi_table[] __initdata = { 130 { 131 .ident = "Google Board", 132 .matches = { 133 DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."), 134 }, 135 }, 136 {} 137 }; 138 MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table); 139 140 static int __init memconsole_init(void) 141 { 142 int ret; 143 144 if (!dmi_check_system(memconsole_dmi_table)) 145 return -ENODEV; 146 147 if (!found_memconsole()) 148 return -ENODEV; 149 150 memconsole_bin_attr.size = memconsole_length; 151 152 ret = sysfs_create_bin_file(firmware_kobj, &memconsole_bin_attr); 153 154 return ret; 155 } 156 157 static void __exit memconsole_exit(void) 158 { 159 sysfs_remove_bin_file(firmware_kobj, &memconsole_bin_attr); 160 } 161 162 module_init(memconsole_init); 163 module_exit(memconsole_exit); 164 165 MODULE_AUTHOR("Google, Inc."); 166 MODULE_LICENSE("GPL"); 167