arch/i386/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  * arch/i386/boot/edd.c
  13  *
  14  * Get EDD BIOS disk information
  15  */
  16
  17 #include "boot.h"
  18 #include <linux/edd.h>
  19
  20 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
  21
  22 /*
  23  * Read the MBR (first sector) from a specific device.
  24  */
  25 static int read_mbr(u8 devno, void *buf)
  26 {
  27         u16 ax, bx, cx, dx;
  28
  29         ax = 0x0201;            /* Legacy Read, one sector */
  30         cx = 0x0001;            /* Sector 0-0-1 */
  31         dx = devno;
  32         bx = (size_t)buf;
  33         asm("pushfl; stc; int $0x13; setc %%al; popfl"
  34             : "+a" (ax), "+c" (cx), "+d" (dx), "+b" (bx)
  35             : : "esi", "edi", "memory");
  36
  37         return -(u8)ax;         /* 0 or -1 */
  38 }
  39
  40 static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
  41 {
  42         int sector_size;
  43         char *mbrbuf_ptr, *mbrbuf_end;
  44         u32 buf_base, mbr_base;
  45         extern char _end[];
  46
  47         sector_size = ei->params.bytes_per_sector;
  48         if (!sector_size)
  49                 sector_size = 512; /* Best available guess */
  50
  51         /* Produce a naturally aligned buffer on the heap */
  52         buf_base = (ds() << 4) + (u32)&_end;
  53         mbr_base = (buf_base+sector_size-1) & ~(sector_size-1);
  54         mbrbuf_ptr = _end + (mbr_base-buf_base);
  55         mbrbuf_end = mbrbuf_ptr + sector_size;
  56
  57         /* Make sure we actually have space on the heap... */
  58         if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))
  59                 return -1;
  60         if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
  61                 return -1;
  62
  63         if (read_mbr(devno, mbrbuf_ptr))
  64                 return -1;
  65
  66         *mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
  67         return 0;
  68 }
  69
  70 static int get_edd_info(u8 devno, struct edd_info *ei)
  71 {
  72         u16 ax, bx, cx, dx, di;
  73
  74         memset(ei, 0, sizeof *ei);
  75
  76         /* Check Extensions Present */
  77
  78         ax = 0x4100;
  79         bx = EDDMAGIC1;
  80         dx = devno;
  81         asm("pushfl; stc; int $0x13; setc %%al; popfl"
  82             : "+a" (ax), "+b" (bx), "=c" (cx), "+d" (dx)
  83             : : "esi", "edi");
  84
  85         if ((u8)ax)
  86                 return -1;      /* No extended information */
  87
  88         if (bx != EDDMAGIC2)
  89                 return -1;
  90
  91         ei->device  = devno;
  92         ei->version = ax >> 8;  /* EDD version number */
  93         ei->interface_support = cx; /* EDD functionality subsets */
  94
  95         /* Extended Get Device Parameters */
  96
  97         ei->params.length = sizeof(ei->params);
  98         ax = 0x4800;
  99         dx = devno;
 100         asm("pushfl; int $0x13; popfl"
 101             : "+a" (ax), "+d" (dx), "=m" (ei->params)
 102             : "S" (&ei->params)
 103             : "ebx", "ecx", "edi");
 104
 105         /* Get legacy CHS parameters */
 106
 107         /* Ralf Brown recommends setting ES:DI to 0:0 */
 108         ax = 0x0800;
 109         dx = devno;
 110         di = 0;
 111         asm("pushw %%es; "
 112             "movw %%di,%%es; "
 113             "pushfl; stc; int $0x13; setc %%al; popfl; "
 114             "popw %%es"
 115             : "+a" (ax), "=b" (bx), "=c" (cx), "+d" (dx), "+D" (di)
 116             : : "esi");
 117
 118         if ((u8)ax == 0) {
 119                 ei->legacy_max_cylinder = (cx >> 8) + ((cx & 0xc0) << 2);
 120                 ei->legacy_max_head = dx >> 8;
 121                 ei->legacy_sectors_per_track = cx & 0x3f;
 122         }
 123
 124         return 0;
 125 }
 126
 127 void query_edd(void)
 128 {
 129         char eddarg[8];
 130         int do_mbr = 1;
 131         int do_edd = 1;
 132         int devno;
 133         struct edd_info ei, *edp;
 134         u32 *mbrptr;
 135
 136         if (cmdline_find_option("edd", eddarg, sizeof eddarg) > 0) {
 137                 if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip"))
 138                         do_mbr = 0;
 139                 else if (!strcmp(eddarg, "off"))
 140                         do_edd = 0;
 141         }
 142
 143         edp    = boot_params.eddbuf;
 144         mbrptr = boot_params.edd_mbr_sig_buffer;
 145
 146         if (!do_edd)
 147                 return;
 148
 149         for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
 150                 /*
 151                  * Scan the BIOS-supported hard disks and query EDD
 152                  * information...
 153                  */
 154                 get_edd_info(devno, &ei);
 155
 156                 if (boot_params.eddbuf_entries < EDDMAXNR) {
 157                         memcpy(edp, &ei, sizeof ei);
 158                         edp++;
 159                         boot_params.eddbuf_entries++;
 160                 }
 161
 162                 if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
 163                         boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;
 164         }
 165 }
 166
 167 #endif