1 /*
2 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License as
6 * published by the Free Software Foundation; either version 2 of the
7 * License, or any later version.
8 *
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
17 */
18
19 FILE_LICENCE ( GPL2_OR_LATER );
20
21 #include <stdint.h>
22 #include <string.h>
23 #include <errno.h>
24 #include <realmode.h>
25 #include <pnpbios.h>
26
27 /** @file
28 *
29 * PnP BIOS
30 *
31 */
32
33 /** PnP BIOS structure */
34 struct pnp_bios {
35 /** Signature
36 *
37 * Must be equal to @c PNP_BIOS_SIGNATURE
38 */
39 uint32_t signature;
40 /** Version as BCD (e.g. 1.0 is 0x10) */
41 uint8_t version;
42 /** Length of this structure */
43 uint8_t length;
44 /** System capabilities */
45 uint16_t control;
46 /** Checksum */
47 uint8_t checksum;
48 } __attribute__ (( packed ));
49
50 /** Signature for a PnP BIOS structure */
51 #define PNP_BIOS_SIGNATURE \
52 ( ( '$' << 0 ) + ( 'P' << 8 ) + ( 'n' << 16 ) + ( 'P' << 24 ) )
53
54 /**
55 * Test address for PnP BIOS structure
56 *
57 * @v offset Offset within BIOS segment to test
58 * @ret rc Return status code
59 */
is_pnp_bios(unsigned int offset)60 static int is_pnp_bios ( unsigned int offset ) {
61 union {
62 struct pnp_bios pnp_bios;
63 uint8_t bytes[256]; /* 256 is maximum length possible */
64 } u;
65 size_t len;
66 unsigned int i;
67 uint8_t sum = 0;
68
69 /* Read start of header and verify signature */
70 copy_from_real ( &u.pnp_bios, BIOS_SEG, offset, sizeof ( u.pnp_bios ));
71 if ( u.pnp_bios.signature != PNP_BIOS_SIGNATURE )
72 return -EINVAL;
73
74 /* Read whole header and verify checksum */
75 len = u.pnp_bios.length;
76 copy_from_real ( &u.bytes, BIOS_SEG, offset, len );
77 for ( i = 0 ; i < len ; i++ ) {
78 sum += u.bytes[i];
79 }
80 if ( sum != 0 )
81 return -EINVAL;
82
83 DBG ( "Found PnP BIOS at %04x:%04x\n", BIOS_SEG, offset );
84
85 return 0;
86 }
87
88 /**
89 * Locate Plug-and-Play BIOS
90 *
91 * @ret pnp_offset Offset of PnP BIOS structure within BIOS segment
92 *
93 * The PnP BIOS structure will be at BIOS_SEG:pnp_offset. If no PnP
94 * BIOS is found, -1 is returned.
95 */
find_pnp_bios(void)96 int find_pnp_bios ( void ) {
97 static int pnp_offset = 0;
98
99 if ( pnp_offset )
100 return pnp_offset;
101
102 for ( pnp_offset = 0 ; pnp_offset < 0x10000 ; pnp_offset += 0x10 ) {
103 if ( is_pnp_bios ( pnp_offset ) == 0 )
104 return pnp_offset;
105 }
106
107 pnp_offset = -1;
108 return pnp_offset;
109 }
110