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 <linux/io.h> 19 #include <asm/bios_ebda.h> 20 21 #define BIOS_MEMCONSOLE_V1_MAGIC 0xDEADBABE 22 #define BIOS_MEMCONSOLE_V2_MAGIC (('M')|('C'<<8)|('O'<<16)|('N'<<24)) 23 24 struct biosmemcon_ebda { 25 u32 signature; 26 union { 27 struct { 28 u8 enabled; 29 u32 buffer_addr; 30 u16 start; 31 u16 end; 32 u16 num_chars; 33 u8 wrapped; 34 } __packed v1; 35 struct { 36 u32 buffer_addr; 37 /* Misdocumented as number of pages! */ 38 u16 num_bytes; 39 u16 start; 40 u16 end; 41 } __packed v2; 42 }; 43 } __packed; 44 45 static u32 memconsole_baseaddr; 46 static size_t memconsole_length; 47 48 static ssize_t memconsole_read(struct file *filp, struct kobject *kobp, 49 struct bin_attribute *bin_attr, char *buf, 50 loff_t pos, size_t count) 51 { 52 char *memconsole; 53 ssize_t ret; 54 55 memconsole = ioremap_cache(memconsole_baseaddr, memconsole_length); 56 if (!memconsole) { 57 pr_err("memconsole: ioremap_cache failed\n"); 58 return -ENOMEM; 59 } 60 ret = memory_read_from_buffer(buf, count, &pos, memconsole, 61 memconsole_length); 62 iounmap(memconsole); 63 return ret; 64 } 65 66 static struct bin_attribute memconsole_bin_attr = { 67 .attr = {.name = "log", .mode = 0444}, 68 .read = memconsole_read, 69 }; 70 71 72 static void __init found_v1_header(struct biosmemcon_ebda *hdr) 73 { 74 pr_info("BIOS console v1 EBDA structure found at %p\n", hdr); 75 pr_info("BIOS console buffer at 0x%.8x, " 76 "start = %d, end = %d, num = %d\n", 77 hdr->v1.buffer_addr, hdr->v1.start, 78 hdr->v1.end, hdr->v1.num_chars); 79 80 memconsole_length = hdr->v1.num_chars; 81 memconsole_baseaddr = hdr->v1.buffer_addr; 82 } 83 84 static void __init found_v2_header(struct biosmemcon_ebda *hdr) 85 { 86 pr_info("BIOS console v2 EBDA structure found at %p\n", hdr); 87 pr_info("BIOS console buffer at 0x%.8x, " 88 "start = %d, end = %d, num_bytes = %d\n", 89 hdr->v2.buffer_addr, hdr->v2.start, 90 hdr->v2.end, hdr->v2.num_bytes); 91 92 memconsole_length = hdr->v2.end - hdr->v2.start; 93 memconsole_baseaddr = hdr->v2.buffer_addr + hdr->v2.start; 94 } 95 96 /* 97 * Search through the EBDA for the BIOS Memory Console, and 98 * set the global variables to point to it. Return true if found. 99 */ 100 static bool __init found_memconsole(void) 101 { 102 unsigned int address; 103 size_t length, cur; 104 105 address = get_bios_ebda(); 106 if (!address) { 107 pr_info("BIOS EBDA non-existent.\n"); 108 return false; 109 } 110 111 /* EBDA length is byte 0 of EBDA (in KB) */ 112 length = *(u8 *)phys_to_virt(address); 113 length <<= 10; /* convert to bytes */ 114 115 /* 116 * Search through EBDA for BIOS memory console structure 117 * note: signature is not necessarily dword-aligned 118 */ 119 for (cur = 0; cur < length; cur++) { 120 struct biosmemcon_ebda *hdr = phys_to_virt(address + cur); 121 122 /* memconsole v1 */ 123 if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) { 124 found_v1_header(hdr); 125 return true; 126 } 127 128 /* memconsole v2 */ 129 if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) { 130 found_v2_header(hdr); 131 return true; 132 } 133 } 134 135 pr_info("BIOS console EBDA structure not found!\n"); 136 return false; 137 } 138 139 static struct dmi_system_id memconsole_dmi_table[] __initdata = { 140 { 141 .ident = "Google Board", 142 .matches = { 143 DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."), 144 }, 145 }, 146 {} 147 }; 148 MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table); 149 150 static int __init memconsole_init(void) 151 { 152 if (!dmi_check_system(memconsole_dmi_table)) 153 return -ENODEV; 154 155 if (!found_memconsole()) 156 return -ENODEV; 157 158 memconsole_bin_attr.size = memconsole_length; 159 return sysfs_create_bin_file(firmware_kobj, &memconsole_bin_attr); 160 } 161 162 static void __exit memconsole_exit(void) 163 { 164 sysfs_remove_bin_file(firmware_kobj, &memconsole_bin_attr); 165 } 166 167 module_init(memconsole_init); 168 module_exit(memconsole_exit); 169 170 MODULE_AUTHOR("Google, Inc."); 171 MODULE_LICENSE("GPL"); 172