arch/x86/boot/edd.c

   1 /* -*- linux-c -*- ------------------------------------------------------- *
   2  *
   3  *   Copyright (C) 1991, 1992 Linus Torvalds
   4  *   Copyright 2007 rPath, Inc. - All Rights Reserved
   5  *
   6  *   This file is part of the Linux kernel, and is made available under
   7  *   the terms of the GNU General Public License version 2.
   8  *
   9  * ----------------------------------------------------------------------- */
  10
  11 /*
  12  * Get EDD BIOS disk information
  13  */
  14
  15 #include "boot.h"
  16 #include <linux/edd.h>
  17
  18 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
  19
  20 /*
  21  * Read the MBR (first sector) from a specific device.
  22  */
  23 static int read_mbr(u8 devno, void *buf)
  24 {
  25         u16 ax, bx, cx, dx;
  26
  27         ax = 0x0201;            /* Legacy Read, one sector */
  28         cx = 0x0001;            /* Sector 0-0-1 */
  29         dx = devno;
  30         bx = (size_t)buf;
  31         asm volatile("pushfl; stc; int $0x13; setc %%al; popfl"
  32                      : "+a" (ax), "+c" (cx), "+d" (dx), "+b" (bx)
  33                      : : "esi", "edi", "memory");
  34
  35         return -(u8)ax;         /* 0 or -1 */
  36 }
  37
  38 static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
  39 {
  40         int sector_size;
  41         char *mbrbuf_ptr, *mbrbuf_end;
  42         u32 buf_base, mbr_base;
  43         extern char _end[];
  44         u16 mbr_magic;
  45
  46         sector_size = ei->params.bytes_per_sector;
  47         if (!sector_size)
  48                 sector_size = 512; /* Best available guess */
  49
  50         /* Produce a naturally aligned buffer on the heap */
  51         buf_base = (ds() << 4) + (u32)&_end;
  52         mbr_base = (buf_base+sector_size-1) & ~(sector_size-1);
  53         mbrbuf_ptr = _end + (mbr_base-buf_base);
  54         mbrbuf_end = mbrbuf_ptr + sector_size;
  55
  56         /* Make sure we actually have space on the heap... */
  57         if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))
  58                 return -1;
  59         if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
  60                 return -1;
  61
  62         memset(mbrbuf_ptr, 0, sector_size);
  63         if (read_mbr(devno, mbrbuf_ptr))
  64                 return -1;
  65
  66         *mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
  67         mbr_magic = *(u16 *)&mbrbuf_ptr[510];
  68
  69         /* check for valid MBR magic */
  70         return mbr_magic == 0xAA55 ? 0 : -1;
  71 }
  72
  73 static int get_edd_info(u8 devno, struct edd_info *ei)
  74 {
  75         u16 ax, bx, cx, dx, di;
  76
  77         memset(ei, 0, sizeof *ei);
  78
  79         /* Check Extensions Present */
  80
  81         ax = 0x4100;
  82         bx = EDDMAGIC1;
  83         dx = devno;
  84         asm("pushfl; stc; int $0x13; setc %%al; popfl"
  85             : "+a" (ax), "+b" (bx), "=c" (cx), "+d" (dx)
  86             : : "esi", "edi");
  87
  88         if ((u8)ax)
  89                 return -1;      /* No extended information */
  90
  91         if (bx != EDDMAGIC2)
  92                 return -1;
  93
  94         ei->device  = devno;
  95         ei->version = ax >> 8;  /* EDD version number */
  96         ei->interface_support = cx; /* EDD functionality subsets */
  97
  98         /* Extended Get Device Parameters */
  99
 100         ei->params.length = sizeof(ei->params);
 101         ax = 0x4800;
 102         dx = devno;
 103         asm("pushfl; int $0x13; popfl"
 104             : "+a" (ax), "+d" (dx), "=m" (ei->params)
 105             : "S" (&ei->params)
 106             : "ebx", "ecx", "edi");
 107
 108         /* Get legacy CHS parameters */
 109
 110         /* Ralf Brown recommends setting ES:DI to 0:0 */
 111         ax = 0x0800;
 112         dx = devno;
 113         di = 0;
 114         asm("pushw %%es; "
 115             "movw %%di,%%es; "
 116             "pushfl; stc; int $0x13; setc %%al; popfl; "
 117             "popw %%es"
 118             : "+a" (ax), "=b" (bx), "=c" (cx), "+d" (dx), "+D" (di)
 119             : : "esi");
 120
 121         if ((u8)ax == 0) {
 122                 ei->legacy_max_cylinder = (cx >> 8) + ((cx & 0xc0) << 2);
 123                 ei->legacy_max_head = dx >> 8;
 124                 ei->legacy_sectors_per_track = cx & 0x3f;
 125         }
 126
 127         return 0;
 128 }
 129
 130 void query_edd(void)
 131 {
 132         char eddarg[8];
 133         int do_mbr = 1;
 134 #ifdef CONFIG_EDD_OFF
 135         int do_edd = 0;
 136 #else
 137         int do_edd = 1;
 138 #endif
 139         int be_quiet;
 140         int devno;
 141         struct edd_info ei, *edp;
 142         u32 *mbrptr;
 143
 144         if (cmdline_find_option("edd", eddarg, sizeof eddarg) > 0) {
 145                 if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip")) {
 146                         do_edd = 1;
 147                         do_mbr = 0;
 148                 }
 149                 else if (!strcmp(eddarg, "off"))
 150                         do_edd = 0;
 151                 else if (!strcmp(eddarg, "on"))
 152                         do_edd = 1;
 153         }
 154
 155         be_quiet = cmdline_find_option_bool("quiet");
 156
 157         edp    = boot_params.eddbuf;
 158         mbrptr = boot_params.edd_mbr_sig_buffer;
 159
 160         if (!do_edd)
 161                 return;
 162
 163         /* Bugs in OnBoard or AddOnCards Bios may hang the EDD probe,
 164          * so give a hint if this happens.
 165          */
 166
 167         if (!be_quiet)
 168                 printf("Probing EDD (edd=off to disable)... ");
 169
 170         for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
 171                 /*
 172                  * Scan the BIOS-supported hard disks and query EDD
 173                  * information...
 174                  */
 175                 if (!get_edd_info(devno, &ei)
 176                     && boot_params.eddbuf_entries < EDDMAXNR) {
 177                         memcpy(edp, &ei, sizeof ei);
 178                         edp++;
 179                         boot_params.eddbuf_entries++;
 180                 }
 181
 182                 if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
 183                         boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;
 184         }
 185
 186         if (!be_quiet)
 187                 printf("ok\n");
 188 }
 189
 190 #endif