apm.c

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/* -*- linux-c -*- ------------------------------------------------------- *
 *
 *   Copyright (C) 1991, 1992 Linus Torvalds
 *   Copyright 2007 rPath, Inc. - All Rights Reserved
 *   Copyright 2009 Intel Corporation; author H. Peter Anvin
 *
 *   Original APM BIOS checking by Stephen Rothwell, May 1994
 *   ([email protected])
 *
 *   This file is part of the Linux kernel, and is made available under
 *   the terms of the GNU General Public License version 2.
 *
 * ----------------------------------------------------------------------- */

/*
 * Get APM BIOS information
 */

#include "boot.h"

int query_apm_bios(void)
{
    struct biosregs ireg, oreg;

    /* APM BIOS installation check */
    initregs(&ireg);
    ireg.ah = 0x53;
    intcall(0x15, &ireg, &oreg);

    if (oreg.flags & X86_EFLAGS_CF)
        return -1;      /* No APM BIOS */

    if (oreg.bx != 0x504d)      /* "PM" signature */
        return -1;

    if (!(oreg.cx & 0x02))      /* 32 bits supported? */
        return -1;

    /* Disconnect first, just in case */
    ireg.al = 0x04;
    intcall(0x15, &ireg, NULL);

    /* 32-bit connect */
    ireg.al = 0x03;
    intcall(0x15, &ireg, &oreg);

    boot_params.apm_bios_info.cseg        = oreg.ax;
    boot_params.apm_bios_info.offset      = oreg.ebx;
    boot_params.apm_bios_info.cseg_16     = oreg.cx;
    boot_params.apm_bios_info.dseg        = oreg.dx;
    boot_params.apm_bios_info.cseg_len    = oreg.si;
    boot_params.apm_bios_info.cseg_16_len = oreg.hsi;
    boot_params.apm_bios_info.dseg_len    = oreg.di;

    if (oreg.flags & X86_EFLAGS_CF)
        return -1;

    /* Redo the installation check as the 32-bit connect;
       some BIOSes return different flags this way... */

    ireg.al = 0x00;
    intcall(0x15, &ireg, &oreg);

    if ((oreg.eflags & X86_EFLAGS_CF) || oreg.bx != 0x504d) {
        /* Failure with 32-bit connect, try to disconect and ignore */
        ireg.al = 0x04;
        intcall(0x15, &ireg, NULL);
        return -1;
    }

    boot_params.apm_bios_info.version = oreg.ax;
    boot_params.apm_bios_info.flags   = oreg.cx;
    return 0;
}