1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc. 4 * 5 * Copyright 1993, 1994 Drew Eckhardt 6 * Visionary Computing 7 * (Unix and Linux consulting and custom programming) 8 * drew@Colorado.EDU 9 * +1 (303) 786-7975 10 * 11 * For more information, please consult the SCSI-CAM draft. 12 */ 13 14 #include <linux/module.h> 15 #include <linux/slab.h> 16 #include <linux/fs.h> 17 #include <linux/genhd.h> 18 #include <linux/kernel.h> 19 #include <linux/blkdev.h> 20 #include <asm/unaligned.h> 21 22 #include <scsi/scsicam.h> 23 24 25 static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds, 26 unsigned int *secs); 27 28 /** 29 * scsi_bios_ptable - Read PC partition table out of first sector of device. 30 * @dev: from this device 31 * 32 * Description: Reads the first sector from the device and returns %0x42 bytes 33 * starting at offset %0x1be. 34 * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error. 35 */ 36 unsigned char *scsi_bios_ptable(struct block_device *dev) 37 { 38 unsigned char *res = kmalloc(66, GFP_KERNEL); 39 if (res) { 40 struct block_device *bdev = dev->bd_contains; 41 Sector sect; 42 void *data = read_dev_sector(bdev, 0, §); 43 if (data) { 44 memcpy(res, data + 0x1be, 66); 45 put_dev_sector(sect); 46 } else { 47 kfree(res); 48 res = NULL; 49 } 50 } 51 return res; 52 } 53 EXPORT_SYMBOL(scsi_bios_ptable); 54 55 /** 56 * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors. 57 * @bdev: which device 58 * @capacity: size of the disk in sectors 59 * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders 60 * 61 * Description : determine the BIOS mapping/geometry used for a drive in a 62 * SCSI-CAM system, storing the results in ip as required 63 * by the HDIO_GETGEO ioctl(). 64 * 65 * Returns : -1 on failure, 0 on success. 66 */ 67 68 int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip) 69 { 70 unsigned char *p; 71 u64 capacity64 = capacity; /* Suppress gcc warning */ 72 int ret; 73 74 p = scsi_bios_ptable(bdev); 75 if (!p) 76 return -1; 77 78 /* try to infer mapping from partition table */ 79 ret = scsi_partsize(p, (unsigned long)capacity, (unsigned int *)ip + 2, 80 (unsigned int *)ip + 0, (unsigned int *)ip + 1); 81 kfree(p); 82 83 if (ret == -1 && capacity64 < (1ULL << 32)) { 84 /* pick some standard mapping with at most 1024 cylinders, 85 and at most 62 sectors per track - this works up to 86 7905 MB */ 87 ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2, 88 (unsigned int *)ip + 0, (unsigned int *)ip + 1); 89 } 90 91 /* if something went wrong, then apparently we have to return 92 a geometry with more than 1024 cylinders */ 93 if (ret || ip[0] > 255 || ip[1] > 63) { 94 if ((capacity >> 11) > 65534) { 95 ip[0] = 255; 96 ip[1] = 63; 97 } else { 98 ip[0] = 64; 99 ip[1] = 32; 100 } 101 102 if (capacity > 65535*63*255) 103 ip[2] = 65535; 104 else 105 ip[2] = (unsigned long)capacity / (ip[0] * ip[1]); 106 } 107 108 return 0; 109 } 110 EXPORT_SYMBOL(scsicam_bios_param); 111 112 /** 113 * scsi_partsize - Parse cylinders/heads/sectors from PC partition table 114 * @buf: partition table, see scsi_bios_ptable() 115 * @capacity: size of the disk in sectors 116 * @cyls: put cylinders here 117 * @hds: put heads here 118 * @secs: put sectors here 119 * 120 * Determine the BIOS mapping/geometry used to create the partition 121 * table, storing the results in @cyls, @hds, and @secs 122 * 123 * Returns: -1 on failure, 0 on success. 124 */ 125 126 int scsi_partsize(unsigned char *buf, unsigned long capacity, 127 unsigned int *cyls, unsigned int *hds, unsigned int *secs) 128 { 129 struct partition *p = (struct partition *)buf, *largest = NULL; 130 int i, largest_cyl; 131 int cyl, ext_cyl, end_head, end_cyl, end_sector; 132 unsigned int logical_end, physical_end, ext_physical_end; 133 134 135 if (*(unsigned short *) (buf + 64) == 0xAA55) { 136 for (largest_cyl = -1, i = 0; i < 4; ++i, ++p) { 137 if (!p->sys_ind) 138 continue; 139 #ifdef DEBUG 140 printk("scsicam_bios_param : partition %d has system \n", 141 i); 142 #endif 143 cyl = p->cyl + ((p->sector & 0xc0) << 2); 144 if (cyl > largest_cyl) { 145 largest_cyl = cyl; 146 largest = p; 147 } 148 } 149 } 150 if (largest) { 151 end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2); 152 end_head = largest->end_head; 153 end_sector = largest->end_sector & 0x3f; 154 155 if (end_head + 1 == 0 || end_sector == 0) 156 return -1; 157 158 #ifdef DEBUG 159 printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n", 160 end_head, end_cyl, end_sector); 161 #endif 162 163 physical_end = end_cyl * (end_head + 1) * end_sector + 164 end_head * end_sector + end_sector; 165 166 /* This is the actual _sector_ number at the end */ 167 logical_end = get_unaligned_le32(&largest->start_sect) 168 + get_unaligned_le32(&largest->nr_sects); 169 170 /* This is for >1023 cylinders */ 171 ext_cyl = (logical_end - (end_head * end_sector + end_sector)) 172 / (end_head + 1) / end_sector; 173 ext_physical_end = ext_cyl * (end_head + 1) * end_sector + 174 end_head * end_sector + end_sector; 175 176 #ifdef DEBUG 177 printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n" 178 ,logical_end, physical_end, ext_physical_end, ext_cyl); 179 #endif 180 181 if ((logical_end == physical_end) || 182 (end_cyl == 1023 && ext_physical_end == logical_end)) { 183 *secs = end_sector; 184 *hds = end_head + 1; 185 *cyls = capacity / ((end_head + 1) * end_sector); 186 return 0; 187 } 188 #ifdef DEBUG 189 printk("scsicam_bios_param : logical (%u) != physical (%u)\n", 190 logical_end, physical_end); 191 #endif 192 } 193 return -1; 194 } 195 EXPORT_SYMBOL(scsi_partsize); 196 197 /* 198 * Function : static int setsize(unsigned long capacity,unsigned int *cyls, 199 * unsigned int *hds, unsigned int *secs); 200 * 201 * Purpose : to determine a near-optimal int 0x13 mapping for a 202 * SCSI disk in terms of lost space of size capacity, storing 203 * the results in *cyls, *hds, and *secs. 204 * 205 * Returns : -1 on failure, 0 on success. 206 * 207 * Extracted from 208 * 209 * WORKING X3T9.2 210 * DRAFT 792D 211 * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf 212 * 213 * Revision 6 214 * 10-MAR-94 215 * Information technology - 216 * SCSI-2 Common access method 217 * transport and SCSI interface module 218 * 219 * ANNEX A : 220 * 221 * setsize() converts a read capacity value to int 13h 222 * head-cylinder-sector requirements. It minimizes the value for 223 * number of heads and maximizes the number of cylinders. This 224 * will support rather large disks before the number of heads 225 * will not fit in 4 bits (or 6 bits). This algorithm also 226 * minimizes the number of sectors that will be unused at the end 227 * of the disk while allowing for very large disks to be 228 * accommodated. This algorithm does not use physical geometry. 229 */ 230 231 static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds, 232 unsigned int *secs) 233 { 234 unsigned int rv = 0; 235 unsigned long heads, sectors, cylinders, temp; 236 237 cylinders = 1024L; /* Set number of cylinders to max */ 238 sectors = 62L; /* Maximize sectors per track */ 239 240 temp = cylinders * sectors; /* Compute divisor for heads */ 241 heads = capacity / temp; /* Compute value for number of heads */ 242 if (capacity % temp) { /* If no remainder, done! */ 243 heads++; /* Else, increment number of heads */ 244 temp = cylinders * heads; /* Compute divisor for sectors */ 245 sectors = capacity / temp; /* Compute value for sectors per 246 track */ 247 if (capacity % temp) { /* If no remainder, done! */ 248 sectors++; /* Else, increment number of sectors */ 249 temp = heads * sectors; /* Compute divisor for cylinders */ 250 cylinders = capacity / temp; /* Compute number of cylinders */ 251 } 252 } 253 if (cylinders == 0) 254 rv = (unsigned) -1; /* Give error if 0 cylinders */ 255 256 *cyls = (unsigned int) cylinders; /* Stuff return values */ 257 *secs = (unsigned int) sectors; 258 *hds = (unsigned int) heads; 259 return (rv); 260 } 261