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