arch/i386/boot/edd.S

   1 /*
   2  * BIOS Enhanced Disk Drive support
   3  * Copyright (C) 2002, 2003, 2004 Dell, Inc.
   4  * by Matt Domsch <Matt_Domsch@dell.com> October 2002
   5  * conformant to T13 Committee www.t13.org
   6  *   projects 1572D, 1484D, 1386D, 1226DT
   7  * disk signature read by Matt Domsch <Matt_Domsch@dell.com>
   8  *      and Andrew Wilks <Andrew_Wilks@dell.com> September 2003, June 2004
   9  * legacy CHS retreival by Patrick J. LoPresti <patl@users.sourceforge.net>
  10  *      March 2004
  11  * Command line option parsing, Matt Domsch, November 2004
  12  */
  13
  14 #include <linux/edd.h>
  15 #include <asm/setup.h>
  16
  17 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
  18         movb    $0, (EDD_MBR_SIG_NR_BUF)
  19         movb    $0, (EDDNR)
  20
  21 # Check the command line for two options:
  22 # edd=of  disables EDD completely  (edd=off)
  23 # edd=sk  skips the MBR test    (edd=skipmbr)
  24         pushl   %esi
  25         cmpl    $0, %cs:cmd_line_ptr
  26         jz      done_cl
  27         movl    %cs:(cmd_line_ptr), %esi
  28 # ds:esi has the pointer to the command line now
  29         movl    $(COMMAND_LINE_SIZE-7), %ecx
  30 # loop through kernel command line one byte at a time
  31 cl_loop:
  32         cmpl    $EDD_CL_EQUALS, (%si)
  33         jz      found_edd_equals
  34         incl    %esi
  35         loop    cl_loop
  36         jmp     done_cl
  37 found_edd_equals:
  38 # only looking at first two characters after equals
  39         addl    $4, %esi
  40         cmpw    $EDD_CL_OFF, (%si)      # edd=of
  41         jz      do_edd_off
  42         cmpw    $EDD_CL_SKIP, (%si)     # edd=sk
  43         jz      do_edd_skipmbr
  44         jmp     done_cl
  45 do_edd_skipmbr:
  46         popl    %esi
  47         jmp     edd_start
  48 do_edd_off:
  49         popl    %esi
  50         jmp     edd_done
  51 done_cl:
  52         popl    %esi
  53
  54
  55 # Read the first sector of each BIOS disk device and store the 4-byte signature
  56 edd_mbr_sig_start:
  57         movb    $0x80, %dl                      # from device 80
  58         movw    $EDD_MBR_SIG_BUF, %bx           # store buffer ptr in bx
  59 edd_mbr_sig_read:
  60         movl    $0xFFFFFFFF, %eax
  61         movl    %eax, (%bx)                     # assume failure
  62         pushw   %bx
  63         movb    $READ_SECTORS, %ah
  64         movb    $1, %al                         # read 1 sector
  65         movb    $0, %dh                         # at head 0
  66         movw    $1, %cx                         # cylinder 0, sector 0
  67         pushw   %es
  68         pushw   %ds
  69         popw    %es
  70         movw    $EDDBUF, %bx                    # disk's data goes into EDDBUF
  71         pushw   %dx             # work around buggy BIOSes
  72         stc                     # work around buggy BIOSes
  73         int     $0x13
  74         sti                     # work around buggy BIOSes
  75         popw    %dx
  76         popw    %es
  77         popw    %bx
  78         jc      edd_mbr_sig_done                # on failure, we're done.
  79         movl    (EDDBUF+EDD_MBR_SIG_OFFSET), %eax # read sig out of the MBR
  80         movl    %eax, (%bx)                     # store success
  81         incb    (EDD_MBR_SIG_NR_BUF)            # note that we stored something
  82         incb    %dl                             # increment to next device
  83         addw    $4, %bx                         # increment sig buffer ptr
  84         cmpb    $EDD_MBR_SIG_MAX, (EDD_MBR_SIG_NR_BUF)  # Out of space?
  85         jb      edd_mbr_sig_read                # keep looping
  86 edd_mbr_sig_done:
  87
  88 # Do the BIOS Enhanced Disk Drive calls
  89 # This consists of two calls:
  90 #    int 13h ah=41h "Check Extensions Present"
  91 #    int 13h ah=48h "Get Device Parameters"
  92 #    int 13h ah=08h "Legacy Get Device Parameters"
  93 #
  94 # A buffer of size EDDMAXNR*(EDDEXTSIZE+EDDPARMSIZE) is reserved for our use
  95 # in the boot_params at EDDBUF.  The first four bytes of which are
  96 # used to store the device number, interface support map and version
  97 # results from fn41.  The next four bytes are used to store the legacy
  98 # cylinders, heads, and sectors from fn08. The following 74 bytes are used to
  99 # store the results from fn48.  Starting from device 80h, fn41, then fn48
 100 # are called and their results stored in EDDBUF+n*(EDDEXTSIZE+EDDPARMIZE).
 101 # Then the pointer is incremented to store the data for the next call.
 102 # This repeats until either a device doesn't exist, or until EDDMAXNR
 103 # devices have been stored.
 104 # The one tricky part is that ds:si always points EDDEXTSIZE bytes into
 105 # the structure, and the fn41 and fn08 results are stored at offsets
 106 # from there.  This removes the need to increment the pointer for
 107 # every store, and leaves it ready for the fn48 call.
 108 # A second one-byte buffer, EDDNR, in the boot_params stores
 109 # the number of BIOS devices which exist, up to EDDMAXNR.
 110 # In setup.c, copy_edd() stores both boot_params buffers away
 111 # for later use, as they would get overwritten otherwise.
 112 # This code is sensitive to the size of the structs in edd.h
 113 edd_start:
 114                                                 # %ds points to the bootsector
 115                                                 # result buffer for fn48
 116         movw    $EDDBUF+EDDEXTSIZE, %si         # in ds:si, fn41 results
 117                                                 # kept just before that
 118         movb    $0x80, %dl                      # BIOS device 0x80
 119
 120 edd_check_ext:
 121         movb    $CHECKEXTENSIONSPRESENT, %ah    # Function 41
 122         movw    $EDDMAGIC1, %bx                 # magic
 123         int     $0x13                           # make the call
 124         jc      edd_done                        # no more BIOS devices
 125
 126         cmpw    $EDDMAGIC2, %bx                 # is magic right?
 127         jne     edd_next                        # nope, next...
 128
 129         movb    %dl, %ds:-8(%si)                # store device number
 130         movb    %ah, %ds:-7(%si)                # store version
 131         movw    %cx, %ds:-6(%si)                # store extensions
 132         incb    (EDDNR)                         # note that we stored something
 133
 134 edd_get_device_params:
 135         movw    $EDDPARMSIZE, %ds:(%si)         # put size
 136         movw    $0x0, %ds:2(%si)                # work around buggy BIOSes
 137         movb    $GETDEVICEPARAMETERS, %ah       # Function 48
 138         int     $0x13                           # make the call
 139                                                 # Don't check for fail return
 140                                                 # it doesn't matter.
 141 edd_get_legacy_chs:
 142         xorw    %ax, %ax
 143         movw    %ax, %ds:-4(%si)
 144         movw    %ax, %ds:-2(%si)
 145         # Ralf Brown's Interrupt List says to set ES:DI to
 146         # 0000h:0000h "to guard against BIOS bugs"
 147         pushw   %es
 148         movw    %ax, %es
 149         movw    %ax, %di
 150         pushw   %dx                             # legacy call clobbers %dl
 151         movb    $LEGACYGETDEVICEPARAMETERS, %ah # Function 08
 152         int     $0x13                           # make the call
 153         jc      edd_legacy_done                 # failed
 154         movb    %cl, %al                        # Low 6 bits are max
 155         andb    $0x3F, %al                      #   sector number
 156         movb    %al, %ds:-1(%si)                # Record max sect
 157         movb    %dh, %ds:-2(%si)                # Record max head number
 158         movb    %ch, %al                        # Low 8 bits of max cyl
 159         shr     $6, %cl
 160         movb    %cl, %ah                        # High 2 bits of max cyl
 161         movw    %ax, %ds:-4(%si)
 162
 163 edd_legacy_done:
 164         popw    %dx
 165         popw    %es
 166         movw    %si, %ax                        # increment si
 167         addw    $EDDPARMSIZE+EDDEXTSIZE, %ax
 168         movw    %ax, %si
 169
 170 edd_next:
 171         incb    %dl                             # increment to next device
 172         cmpb    $EDDMAXNR, (EDDNR)              # Out of space?
 173         jb      edd_check_ext                   # keep looping
 174
 175 edd_done:
 176 #endif