drivers/firmware/google/memconsole.c

   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");