drivers/firmware/google/memconsole-x86-legacy.c

   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 <linux/acpi.h>
  24
  25 #include "memconsole.h"
  26
  27 #define BIOS_MEMCONSOLE_V1_MAGIC        0xDEADBABE
  28 #define BIOS_MEMCONSOLE_V2_MAGIC        (('M')|('C'<<8)|('O'<<16)|('N'<<24))
  29
  30 struct biosmemcon_ebda {
  31         u32 signature;
  32         union {
  33                 struct {
  34                         u8  enabled;
  35                         u32 buffer_addr;
  36                         u16 start;
  37                         u16 end;
  38                         u16 num_chars;
  39                         u8  wrapped;
  40                 } __packed v1;
  41                 struct {
  42                         u32 buffer_addr;
  43                         /* Misdocumented as number of pages! */
  44                         u16 num_bytes;
  45                         u16 start;
  46                         u16 end;
  47                 } __packed v2;
  48         };
  49 } __packed;
  50
  51 static char *memconsole_baseaddr;
  52 static size_t memconsole_length;
  53
  54 static ssize_t memconsole_read(char *buf, loff_t pos, size_t count)
  55 {
  56         return memory_read_from_buffer(buf, count, &pos, memconsole_baseaddr,
  57                                        memconsole_length);
  58 }
  59
  60 static void found_v1_header(struct biosmemcon_ebda *hdr)
  61 {
  62         pr_info("memconsole: BIOS console v1 EBDA structure found at %p\n",
  63                 hdr);
  64         pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num = %d\n",
  65                 hdr->v1.buffer_addr, hdr->v1.start,
  66                 hdr->v1.end, hdr->v1.num_chars);
  67
  68         memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr);
  69         memconsole_length = hdr->v1.num_chars;
  70         memconsole_setup(memconsole_read);
  71 }
  72
  73 static void found_v2_header(struct biosmemcon_ebda *hdr)
  74 {
  75         pr_info("memconsole: BIOS console v2 EBDA structure found at %p\n",
  76                 hdr);
  77         pr_info("memconsole: BIOS console buffer at 0x%.8x, 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_baseaddr = phys_to_virt(hdr->v2.buffer_addr + hdr->v2.start);
  82         memconsole_length = hdr->v2.end - hdr->v2.start;
  83         memconsole_setup(memconsole_read);
  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 memconsole_ebda_init(void)
  91 {
  92         unsigned int address;
  93         size_t length, cur;
  94
  95         address = get_bios_ebda();
  96         if (!address) {
  97                 pr_info("memconsole: 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         pr_info("memconsole: 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 bool __init memconsole_find(void)
 141 {
 142         if (!dmi_check_system(memconsole_dmi_table))
 143                 return false;
 144
 145         return memconsole_ebda_init();
 146 }
 147
 148 static int __init memconsole_x86_init(void)
 149 {
 150         if (!memconsole_find())
 151                 return -ENODEV;
 152
 153         return memconsole_sysfs_init();
 154 }
 155
 156 static void __exit memconsole_x86_exit(void)
 157 {
 158         memconsole_exit();
 159 }
 160
 161 module_init(memconsole_x86_init);
 162 module_exit(memconsole_x86_exit);
 163
 164 MODULE_AUTHOR("Google, Inc.");
 165 MODULE_LICENSE("GPL");