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 */
23static 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
38static 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
73static 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
120void 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