xref: /openbmc/linux/arch/x86/boot/edd.c (revision 97873a3d)
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  */
read_mbr(u8 devno,void * buf)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 
read_mbr_sig(u8 devno,struct edd_info * ei,u32 * mbrsig)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 
get_edd_info(u8 devno,struct edd_info * ei)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 
query_edd(void)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