arch/x86/boot/apm.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  *   Original APM BIOS checking by Stephen Rothwell, May 1994
   9  *   ([email protected])
  10  *
  11  * ----------------------------------------------------------------------- */
  12
  13 /*
  14  * Get APM BIOS information
  15  */
  16
  17 #include "boot.h"
  18
  19 int query_apm_bios(void)
  20 {
  21         struct biosregs ireg, oreg;
  22
  23         /* APM BIOS installation check */
  24         initregs(&ireg);
  25         ireg.ah = 0x53;
  26         intcall(0x15, &ireg, &oreg);
  27
  28         if (oreg.flags & X86_EFLAGS_CF)
  29                 return -1;              /* No APM BIOS */
  30
  31         if (oreg.bx != 0x504d)          /* "PM" signature */
  32                 return -1;
  33
  34         if (!(oreg.cx & 0x02))          /* 32 bits supported? */
  35                 return -1;
  36
  37         /* Disconnect first, just in case */
  38         ireg.al = 0x04;
  39         intcall(0x15, &ireg, NULL);
  40
  41         /* 32-bit connect */
  42         ireg.al = 0x03;
  43         intcall(0x15, &ireg, &oreg);
  44
  45         boot_params.apm_bios_info.cseg        = oreg.ax;
  46         boot_params.apm_bios_info.offset      = oreg.ebx;
  47         boot_params.apm_bios_info.cseg_16     = oreg.cx;
  48         boot_params.apm_bios_info.dseg        = oreg.dx;
  49         boot_params.apm_bios_info.cseg_len    = oreg.si;
  50         boot_params.apm_bios_info.cseg_16_len = oreg.hsi;
  51         boot_params.apm_bios_info.dseg_len    = oreg.di;
  52
  53         if (oreg.flags & X86_EFLAGS_CF)
  54                 return -1;
  55
  56         /* Redo the installation check as the 32-bit connect;
  57            some BIOSes return different flags this way... */
  58
  59         ireg.al = 0x00;
  60         intcall(0x15, &ireg, &oreg);
  61
  62         if ((oreg.eflags & X86_EFLAGS_CF) || oreg.bx != 0x504d) {
  63                 /* Failure with 32-bit connect, try to disconnect and ignore */
  64                 ireg.al = 0x04;
  65                 intcall(0x15, &ireg, NULL);
  66                 return -1;
  67         }
  68
  69         boot_params.apm_bios_info.version = oreg.ax;
  70         boot_params.apm_bios_info.flags   = oreg.cx;
  71         return 0;
  72 }
  73