x86/boot/edd.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /* -*- linux-c -*- ------------------------------------------------------- *
0003  *
0004  *   Copyright (C) 1991, 1992 Linus Torvalds
0005  *   Copyright 2007 rPath, Inc. - All Rights Reserved
0006  *   Copyright 2009 Intel Corporation; author H. Peter Anvin
0007  *
0008  * ----------------------------------------------------------------------- */
0009
0010 /*
0011  * Get EDD BIOS disk information
0012  */
0013
0014 #include "boot.h"
0015 #include <linux/edd.h>
0016 #include "string.h"
0017
0018 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
0019
0020 /*
0021  * Read the MBR (first sector) from a specific device.
0022  */
0023 static int read_mbr(u8 devno, void *buf)
0024 {
0025     struct biosregs ireg, oreg;
0026
0027     initregs(&ireg);
0028     ireg.ax = 0x0201;       /* Legacy Read, one sector */
0029     ireg.cx = 0x0001;       /* Sector 0-0-1 */
0030     ireg.dl = devno;
0031     ireg.bx = (size_t)buf;
0032
0033     intcall(0x13, &ireg, &oreg);
0034
0035     return -(oreg.eflags & X86_EFLAGS_CF); /* 0 or -1 */
0036 }
0037
0038 static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
0039 {
0040     int sector_size;
0041     char *mbrbuf_ptr, *mbrbuf_end;
0042     u32 buf_base, mbr_base;
0043     extern char _end[];
0044     u16 mbr_magic;
0045
0046     sector_size = ei->params.bytes_per_sector;
0047     if (!sector_size)
0048         sector_size = 512; /* Best available guess */
0049
0050     /* Produce a naturally aligned buffer on the heap */
0051     buf_base = (ds() << 4) + (u32)&_end;
0052     mbr_base = (buf_base+sector_size-1) & ~(sector_size-1);
0053     mbrbuf_ptr = _end + (mbr_base-buf_base);
0054     mbrbuf_end = mbrbuf_ptr + sector_size;
0055
0056     /* Make sure we actually have space on the heap... */
0057     if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))
0058         return -1;
0059     if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
0060         return -1;
0061
0062     memset(mbrbuf_ptr, 0, sector_size);
0063     if (read_mbr(devno, mbrbuf_ptr))
0064         return -1;
0065
0066     *mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
0067     mbr_magic = *(u16 *)&mbrbuf_ptr[510];
0068
0069     /* check for valid MBR magic */
0070     return mbr_magic == 0xAA55 ? 0 : -1;
0071 }
0072
0073 static int get_edd_info(u8 devno, struct edd_info *ei)
0074 {
0075     struct biosregs ireg, oreg;
0076
0077     memset(ei, 0, sizeof(*ei));
0078
0079     /* Check Extensions Present */
0080
0081     initregs(&ireg);
0082     ireg.ah = 0x41;
0083     ireg.bx = EDDMAGIC1;
0084     ireg.dl = devno;
0085     intcall(0x13, &ireg, &oreg);
0086
0087     if (oreg.eflags & X86_EFLAGS_CF)
0088         return -1;  /* No extended information */
0089
0090     if (oreg.bx != EDDMAGIC2)
0091         return -1;
0092
0093     ei->device  = devno;
0094     ei->version = oreg.ah;       /* EDD version number */
0095     ei->interface_support = oreg.cx; /* EDD functionality subsets */
0096
0097     /* Extended Get Device Parameters */
0098
0099     ei->params.length = sizeof(ei->params);
0100     ireg.ah = 0x48;
0101     ireg.si = (size_t)&ei->params;
0102     intcall(0x13, &ireg, &oreg);
0103
0104     /* Get legacy CHS parameters */
0105
0106     /* Ralf Brown recommends setting ES:DI to 0:0 */
0107     ireg.ah = 0x08;
0108     ireg.es = 0;
0109     intcall(0x13, &ireg, &oreg);
0110
0111     if (!(oreg.eflags & X86_EFLAGS_CF)) {
0112         ei->legacy_max_cylinder = oreg.ch + ((oreg.cl & 0xc0) << 2);
0113         ei->legacy_max_head = oreg.dh;
0114         ei->legacy_sectors_per_track = oreg.cl & 0x3f;
0115     }
0116
0117     return 0;
0118 }
0119
0120 void query_edd(void)
0121 {
0122     char eddarg[8];
0123     int do_mbr = 1;
0124 #ifdef CONFIG_EDD_OFF
0125     int do_edd = 0;
0126 #else
0127     int do_edd = 1;
0128 #endif
0129     int be_quiet;
0130     int devno;
0131     struct edd_info ei, *edp;
0132     u32 *mbrptr;
0133
0134     if (cmdline_find_option("edd", eddarg, sizeof(eddarg)) > 0) {
0135         if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip")) {
0136             do_edd = 1;
0137             do_mbr = 0;
0138         }
0139         else if (!strcmp(eddarg, "off"))
0140             do_edd = 0;
0141         else if (!strcmp(eddarg, "on"))
0142             do_edd = 1;
0143     }
0144
0145     be_quiet = cmdline_find_option_bool("quiet");
0146
0147     edp    = boot_params.eddbuf;
0148     mbrptr = boot_params.edd_mbr_sig_buffer;
0149
0150     if (!do_edd)
0151         return;
0152
0153     /* Bugs in OnBoard or AddOnCards Bios may hang the EDD probe,
0154      * so give a hint if this happens.
0155      */
0156
0157     if (!be_quiet)
0158         printf("Probing EDD (edd=off to disable)... ");
0159
0160     for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
0161         /*
0162          * Scan the BIOS-supported hard disks and query EDD
0163          * information...
0164          */
0165         if (!get_edd_info(devno, &ei)
0166             && boot_params.eddbuf_entries < EDDMAXNR) {
0167             memcpy(edp, &ei, sizeof(ei));
0168             edp++;
0169             boot_params.eddbuf_entries++;
0170         }
0171
0172         if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
0173             boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;
0174     }
0175
0176     if (!be_quiet)
0177         printf("ok\n");
0178 }
0179
0180 #endif