root/arch/x86/boot/edd.c

DEFINITIONS

1. read_mbr
2. read_mbr_sig
3. get_edd_info
4. query_edd

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* -*- linux-c -*- ------------------------------------------------------- *
   3  *
   4  *   Copyright (C) 1991, 1992 Linus Torvalds
   5  *   Copyright 2007 rPath, Inc. - All Rights Reserved
   6  *   Copyright 2009 Intel Corporation; author H. Peter Anvin
   7  *
   8  * ----------------------------------------------------------------------- */
   9 
  10 /*
  11  * Get EDD BIOS disk information
  12  */
  13 
  14 #include "boot.h"
  15 #include <linux/edd.h>
  16 #include "string.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         struct biosregs ireg, oreg;
  26 
  27         initregs(&ireg);
  28         ireg.ax = 0x0201;               /* Legacy Read, one sector */
  29         ireg.cx = 0x0001;               /* Sector 0-0-1 */
  30         ireg.dl = devno;
  31         ireg.bx = (size_t)buf;
  32 
  33         intcall(0x13, &ireg, &oreg);
  34 
  35         return -(oreg.eflags & X86_EFLAGS_CF); /* 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         struct biosregs ireg, oreg;
  76 
  77         memset(ei, 0, sizeof(*ei));
  78 
  79         /* Check Extensions Present */
  80 
  81         initregs(&ireg);
  82         ireg.ah = 0x41;
  83         ireg.bx = EDDMAGIC1;
  84         ireg.dl = devno;
  85         intcall(0x13, &ireg, &oreg);
  86 
  87         if (oreg.eflags & X86_EFLAGS_CF)
  88                 return -1;      /* No extended information */
  89 
  90         if (oreg.bx != EDDMAGIC2)
  91                 return -1;
  92 
  93         ei->device  = devno;
  94         ei->version = oreg.ah;           /* EDD version number */
  95         ei->interface_support = oreg.cx; /* EDD functionality subsets */
  96 
  97         /* Extended Get Device Parameters */
  98 
  99         ei->params.length = sizeof(ei->params);
 100         ireg.ah = 0x48;
 101         ireg.si = (size_t)&ei->params;
 102         intcall(0x13, &ireg, &oreg);
 103 
 104         /* Get legacy CHS parameters */
 105 
 106         /* Ralf Brown recommends setting ES:DI to 0:0 */
 107         ireg.ah = 0x08;
 108         ireg.es = 0;
 109         intcall(0x13, &ireg, &oreg);
 110 
 111         if (!(oreg.eflags & X86_EFLAGS_CF)) {
 112                 ei->legacy_max_cylinder = oreg.ch + ((oreg.cl & 0xc0) << 2);
 113                 ei->legacy_max_head = oreg.dh;
 114                 ei->legacy_sectors_per_track = oreg.cl & 0x3f;
 115         }
 116 
 117         return 0;
 118 }
 119 
 120 void query_edd(void)
 121 {
 122         char eddarg[8];
 123         int do_mbr = 1;
 124 #ifdef CONFIG_EDD_OFF
 125         int do_edd = 0;
 126 #else
 127         int do_edd = 1;
 128 #endif
 129         int be_quiet;
 130         int devno;
 131         struct edd_info ei, *edp;
 132         u32 *mbrptr;
 133 
 134         if (cmdline_find_option("edd", eddarg, sizeof(eddarg)) > 0) {
 135                 if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip")) {
 136                         do_edd = 1;
 137                         do_mbr = 0;
 138                 }
 139                 else if (!strcmp(eddarg, "off"))
 140                         do_edd = 0;
 141                 else if (!strcmp(eddarg, "on"))
 142                         do_edd = 1;
 143         }
 144 
 145         be_quiet = cmdline_find_option_bool("quiet");
 146 
 147         edp    = boot_params.eddbuf;
 148         mbrptr = boot_params.edd_mbr_sig_buffer;
 149 
 150         if (!do_edd)
 151                 return;
 152 
 153         /* Bugs in OnBoard or AddOnCards Bios may hang the EDD probe,
 154          * so give a hint if this happens.
 155          */
 156 
 157         if (!be_quiet)
 158                 printf("Probing EDD (edd=off to disable)... ");
 159 
 160         for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
 161                 /*
 162                  * Scan the BIOS-supported hard disks and query EDD
 163                  * information...
 164                  */
 165                 if (!get_edd_info(devno, &ei)
 166                     && boot_params.eddbuf_entries < EDDMAXNR) {
 167                         memcpy(edp, &ei, sizeof(ei));
 168                         edp++;
 169                         boot_params.eddbuf_entries++;
 170                 }
 171 
 172                 if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
 173                         boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;
 174         }
 175 
 176         if (!be_quiet)
 177                 printf("ok\n");
 178 }
 179 
 180 #endif