1 // SPDX-License-Identifier: GPL-2.0-only
2 /* -*- linux-c -*- ------------------------------------------------------- *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 * Copyright 2007 rPath, Inc. - All Rights Reserved
6 * Copyright 2009 Intel Corporation; author H. Peter Anvin
8 * ----------------------------------------------------------------------- */
11 * Get EDD BIOS disk information
15 #include <linux/edd.h>
18 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
21 * Read the MBR (first sector) from a specific device.
23 static int read_mbr(u8 devno, void *buf)
25 struct biosregs ireg, oreg;
28 ireg.ax = 0x0201; /* Legacy Read, one sector */
29 ireg.cx = 0x0001; /* Sector 0-0-1 */
31 ireg.bx = (size_t)buf;
33 intcall(0x13, &ireg, &oreg);
35 return -(oreg.eflags & X86_EFLAGS_CF); /* 0 or -1 */
38 static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
41 char *mbrbuf_ptr, *mbrbuf_end;
42 u32 buf_base, mbr_base;
46 sector_size = ei->params.bytes_per_sector;
48 sector_size = 512; /* Best available guess */
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;
56 /* Make sure we actually have space on the heap... */
57 if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))
59 if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
62 memset(mbrbuf_ptr, 0, sector_size);
63 if (read_mbr(devno, mbrbuf_ptr))
66 *mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
67 mbr_magic = *(u16 *)&mbrbuf_ptr[510];
69 /* check for valid MBR magic */
70 return mbr_magic == 0xAA55 ? 0 : -1;
73 static int get_edd_info(u8 devno, struct edd_info *ei)
75 struct biosregs ireg, oreg;
77 memset(ei, 0, sizeof(*ei));
79 /* Check Extensions Present */
85 intcall(0x13, &ireg, &oreg);
87 if (oreg.eflags & X86_EFLAGS_CF)
88 return -1; /* No extended information */
90 if (oreg.bx != EDDMAGIC2)
94 ei->version = oreg.ah; /* EDD version number */
95 ei->interface_support = oreg.cx; /* EDD functionality subsets */
97 /* Extended Get Device Parameters */
99 ei->params.length = sizeof(ei->params);
101 ireg.si = (size_t)&ei->params;
102 intcall(0x13, &ireg, &oreg);
104 /* Get legacy CHS parameters */
106 /* Ralf Brown recommends setting ES:DI to 0:0 */
109 intcall(0x13, &ireg, &oreg);
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;
124 #ifdef CONFIG_EDD_OFF
131 struct edd_info ei, *edp;
134 if (cmdline_find_option("edd", eddarg, sizeof(eddarg)) > 0) {
135 if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip")) {
139 else if (!strcmp(eddarg, "off"))
141 else if (!strcmp(eddarg, "on"))
145 be_quiet = cmdline_find_option_bool("quiet");
147 edp = boot_params.eddbuf;
148 mbrptr = boot_params.edd_mbr_sig_buffer;
153 /* Bugs in OnBoard or AddOnCards Bios may hang the EDD probe,
154 * so give a hint if this happens.
158 printf("Probing EDD (edd=off to disable)... ");
160 for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
162 * Scan the BIOS-supported hard disks and query EDD
165 if (!get_edd_info(devno, &ei)
166 && boot_params.eddbuf_entries < EDDMAXNR) {
167 memcpy(edp, &ei, sizeof(ei));
169 boot_params.eddbuf_entries++;
172 if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
173 boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;