LXR linux/arch/x86/boot/edd.c

   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 */
  23static 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
  38static 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
  73static 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
 120void 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
 181