linux/arch/x86/boot/edd.c
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   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 */
  23static 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
  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        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
 130void 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
 191