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