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  *   (sfr@canb.auug.org.au)
10  *
11  * ----------------------------------------------------------------------- */
12 
13 /*
14  * Get APM BIOS information
15  */
16 
17 #include "boot.h"
18 
query_apm_bios(void)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 
74