arch/x86/lib/realmode.c

   1 /*
   2  * (C) Copyright 2002
   3  * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se>
   4  *
   5  * See file CREDITS for list of people who contributed to this
   6  * project.
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License as
  10  * published by the Free Software Foundation; either version 2 of
  11  * the License, or (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  21  * MA 02111-1307 USA
  22  */
  23
  24 #include <common.h>
  25 #include <asm/io.h>
  26 #include <asm/ptrace.h>
  27 #include <asm/realmode.h>
  28
  29 #define REALMODE_MAILBOX ((char *)0xe00)
  30
  31 int realmode_setup(void)
  32 {
  33         /*
  34          * The realmode section is not relocated and still in the ROM. The
  35          * __realmode_start symbol was adjusted, though, so adjust it back.
  36          */
  37         ulong realmode_start = (ulong)&__realmode_start - gd->reloc_off;
  38         ulong realmode_size = (ulong)&__realmode_size;
  39
  40         /* copy the realmode switch code */
  41         if (realmode_size > (REALMODE_MAILBOX - (char *)REALMODE_BASE)) {
  42                 printf("realmode switch too large (%ld bytes, max is %d)\n",
  43                        realmode_size,
  44                        (int)(REALMODE_MAILBOX - (char *)REALMODE_BASE));
  45                 return -1;
  46         }
  47
  48         memcpy((char *)REALMODE_BASE, (void *)realmode_start, realmode_size);
  49         asm("wbinvd\n");
  50
  51         return 0;
  52 }
  53
  54 int enter_realmode(u16 seg, u16 off, struct pt_regs *in, struct pt_regs *out)
  55 {
  56
  57         /* setup out thin bios emulation */
  58         if (bios_setup())
  59                 return -1;
  60
  61         if (realmode_setup())
  62                 return -1;
  63
  64         in->eip = off;
  65         in->xcs = seg;
  66         if ((in->esp & 0xffff) < 4)
  67                 printf("Warning: entering realmode with sp < 4 will fail\n");
  68
  69         memcpy(REALMODE_MAILBOX, in, sizeof(struct pt_regs));
  70         asm("wbinvd\n");
  71
  72         __asm__ volatile (
  73                  "lcall $0x20,%0\n" : : "i" (&realmode_enter));
  74
  75         asm("wbinvd\n");
  76         memcpy(out, REALMODE_MAILBOX, sizeof(struct pt_regs));
  77
  78         return out->eax;
  79 }
  80
  81 /*
  82  * This code is supposed to access a realmode interrupt
  83  * it does currently not work for me
  84  */
  85 int enter_realmode_int(u8 lvl, struct pt_regs *in, struct pt_regs *out)
  86 {
  87         /* place two instructions at 0x700 */
  88         writeb(0xcd, 0x700);  /* int $lvl */
  89         writeb(lvl, 0x701);
  90         writeb(0xcb, 0x702);  /* lret */
  91         asm("wbinvd\n");
  92
  93         enter_realmode(0x00, 0x700, in, out);
  94
  95         return out->eflags & 0x00000001;
  96 }