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 <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");