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 * ----------------------------------------------------------------------- */
9
10 /*
11 * Get EDD BIOS disk information
12 */
13
14 #include "boot.h"
15 #include <linux/edd.h>
16 #include "string.h"
17
18 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
19
20 /*
21 * Read the MBR (first sector) from a specific device.
22 */
23 static int read_mbr(u8 devno, void *buf)
24 {
25 struct biosregs ireg, oreg;
26
27 initregs(&ireg);
28 ireg.ax = 0x0201; /* Legacy Read, one sector */
29 ireg.cx = 0x0001; /* Sector 0-0-1 */
30 ireg.dl = devno;
31 ireg.bx = (size_t)buf;
32
33 intcall(0x13, &ireg, &oreg);
34
35 return -(oreg.eflags & X86_EFLAGS_CF); /* 0 or -1 */
36 }
37
38 static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
39 {
40 int sector_size;
41 char *mbrbuf_ptr, *mbrbuf_end;
42 u32 buf_base, mbr_base;
43 extern char _end[];
44 u16 mbr_magic;
45
46 sector_size = ei->params.bytes_per_sector;
47 if (!sector_size)
48 sector_size = 512; /* Best available guess */
49
50 /* Produce a naturally aligned buffer on the heap */
51 buf_base = (ds() << 4) + (u32)&_end;
52 mbr_base = (buf_base+sector_size-1) & ~(sector_size-1);
53 mbrbuf_ptr = _end + (mbr_base-buf_base);
54 mbrbuf_end = mbrbuf_ptr + sector_size;
55
56 /* Make sure we actually have space on the heap... */
57 if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))
58 return -1;
59 if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
60 return -1;
61
62 memset(mbrbuf_ptr, 0, sector_size);
63 if (read_mbr(devno, mbrbuf_ptr))
64 return -1;
65
66 *mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
67 mbr_magic = *(u16 *)&mbrbuf_ptr[510];
68
69 /* check for valid MBR magic */
70 return mbr_magic == 0xAA55 ? 0 : -1;
71 }
72
73 static int get_edd_info(u8 devno, struct edd_info *ei)
74 {
75 struct biosregs ireg, oreg;
76
77 memset(ei, 0, sizeof(*ei));
78
79 /* Check Extensions Present */
80
81 initregs(&ireg);
82 ireg.ah = 0x41;
83 ireg.bx = EDDMAGIC1;
84 ireg.dl = devno;
85 intcall(0x13, &ireg, &oreg);
86
87 if (oreg.eflags & X86_EFLAGS_CF)
88 return -1; /* No extended information */
89
90 if (oreg.bx != EDDMAGIC2)
91 return -1;
92
93 ei->device = devno;
94 ei->version = oreg.ah; /* EDD version number */
95 ei->interface_support = oreg.cx; /* EDD functionality subsets */
96
97 /* Extended Get Device Parameters */
98
99 ei->params.length = sizeof(ei->params);
100 ireg.ah = 0x48;
101 ireg.si = (size_t)&ei->params;
102 intcall(0x13, &ireg, &oreg);
103
104 /* Get legacy CHS parameters */
105
106 /* Ralf Brown recommends setting ES:DI to 0:0 */
107 ireg.ah = 0x08;
108 ireg.es = 0;
109 intcall(0x13, &ireg, &oreg);
110
111 if (!(oreg.eflags & X86_EFLAGS_CF)) {
112 ei->legacy_max_cylinder = oreg.ch + ((oreg.cl & 0xc0) << 2);
113 ei->legacy_max_head = oreg.dh;
114 ei->legacy_sectors_per_track = oreg.cl & 0x3f;
115 }
116
117 return 0;
118 }
119
120 void query_edd(void)
121 {
122 char eddarg[8];
123 int do_mbr = 1;
124 #ifdef CONFIG_EDD_OFF
125 int do_edd = 0;
126 #else
127 int do_edd = 1;
128 #endif
129 int be_quiet;
130 int devno;
131 struct edd_info ei, *edp;
132 u32 *mbrptr;
133
134 if (cmdline_find_option("edd", eddarg, sizeof(eddarg)) > 0) {
135 if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip")) {
136 do_edd = 1;
137 do_mbr = 0;
138 }
139 else if (!strcmp(eddarg, "off"))
140 do_edd = 0;
141 else if (!strcmp(eddarg, "on"))
142 do_edd = 1;
143 }
144
145 be_quiet = cmdline_find_option_bool("quiet");
146
147 edp = boot_params.eddbuf;
148 mbrptr = boot_params.edd_mbr_sig_buffer;
149
150 if (!do_edd)
151 return;
152
153 /* Bugs in OnBoard or AddOnCards Bios may hang the EDD probe,
154 * so give a hint if this happens.
155 */
156
157 if (!be_quiet)
158 printf("Probing EDD (edd=off to disable)... ");
159
160 for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
161 /*
162 * Scan the BIOS-supported hard disks and query EDD
163 * information...
164 */
165 if (!get_edd_info(devno, &ei)
166 && boot_params.eddbuf_entries < EDDMAXNR) {
167 memcpy(edp, &ei, sizeof(ei));
168 edp++;
169 boot_params.eddbuf_entries++;
170 }
171
172 if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
173 boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;
174 }
175
176 if (!be_quiet)
177 printf("ok\n");
178 }
179
180 #endif
181
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