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1// SPDX-License-Identifier: GPL-2.02/*3 * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc.4 *5 * Copyright 1993, 1994 Drew Eckhardt6 * Visionary Computing 7 * (Unix and Linux consulting and custom programming)8 * drew@Colorado.EDU9 * +1 (303) 786-797510 *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/kernel.h>18#include <linux/blkdev.h>19#include <linux/pagemap.h>20#include <linux/msdos_partition.h>21#include <linux/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 device28 *29 * Description: Reads the first sector from the device and returns %0x42 bytes30 * starting at offset %0x1be.31 * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error.32 */33unsigned char *scsi_bios_ptable(struct block_device *dev)34{35 struct address_space *mapping = bdev_whole(dev)->bd_mapping;36 unsigned char *res = NULL;37 struct folio *folio;38 39 folio = read_mapping_folio(mapping, 0, NULL);40 if (IS_ERR(folio))41 return NULL;42 43 res = kmemdup(folio_address(folio) + 0x1be, 66, GFP_KERNEL);44 folio_put(folio);45 return res;46}47EXPORT_SYMBOL(scsi_bios_ptable);48 49/**50 * scsi_partsize - Parse cylinders/heads/sectors from PC partition table51 * @bdev: block device to parse52 * @capacity: size of the disk in sectors53 * @geom: output in form of [hds, cylinders, sectors]54 *55 * Determine the BIOS mapping/geometry used to create the partition56 * table, storing the results in @geom.57 *58 * Returns: %false on failure, %true on success.59 */60bool scsi_partsize(struct block_device *bdev, sector_t capacity, int geom[3])61{62 int cyl, ext_cyl, end_head, end_cyl, end_sector;63 unsigned int logical_end, physical_end, ext_physical_end;64 struct msdos_partition *p, *largest = NULL;65 void *buf;66 int ret = false;67 68 buf = scsi_bios_ptable(bdev);69 if (!buf)70 return false;71 72 if (*(unsigned short *) (buf + 64) == 0xAA55) {73 int largest_cyl = -1, i;74 75 for (i = 0, p = buf; i < 4; i++, p++) {76 if (!p->sys_ind)77 continue;78#ifdef DEBUG79 printk("scsicam_bios_param : partition %d has system \n",80 i);81#endif82 cyl = p->cyl + ((p->sector & 0xc0) << 2);83 if (cyl > largest_cyl) {84 largest_cyl = cyl;85 largest = p;86 }87 }88 }89 if (largest) {90 end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);91 end_head = largest->end_head;92 end_sector = largest->end_sector & 0x3f;93 94 if (end_head + 1 == 0 || end_sector == 0)95 goto out_free_buf;96 97#ifdef DEBUG98 printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",99 end_head, end_cyl, end_sector);100#endif101 102 physical_end = end_cyl * (end_head + 1) * end_sector +103 end_head * end_sector + end_sector;104 105 /* This is the actual _sector_ number at the end */106 logical_end = get_unaligned_le32(&largest->start_sect)107 + get_unaligned_le32(&largest->nr_sects);108 109 /* This is for >1023 cylinders */110 ext_cyl = (logical_end - (end_head * end_sector + end_sector))111 / (end_head + 1) / end_sector;112 ext_physical_end = ext_cyl * (end_head + 1) * end_sector +113 end_head * end_sector + end_sector;114 115#ifdef DEBUG116 printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n"117 ,logical_end, physical_end, ext_physical_end, ext_cyl);118#endif119 120 if (logical_end == physical_end ||121 (end_cyl == 1023 && ext_physical_end == logical_end)) {122 geom[0] = end_head + 1;123 geom[1] = end_sector;124 geom[2] = (unsigned long)capacity /125 ((end_head + 1) * end_sector);126 ret = true;127 goto out_free_buf;128 }129#ifdef DEBUG130 printk("scsicam_bios_param : logical (%u) != physical (%u)\n",131 logical_end, physical_end);132#endif133 }134 135out_free_buf:136 kfree(buf);137 return ret;138}139EXPORT_SYMBOL(scsi_partsize);140 141/*142 * Function : static int setsize(unsigned long capacity,unsigned int *cyls,143 * unsigned int *hds, unsigned int *secs);144 *145 * Purpose : to determine a near-optimal int 0x13 mapping for a146 * SCSI disk in terms of lost space of size capacity, storing147 * the results in *cyls, *hds, and *secs.148 *149 * Returns : -1 on failure, 0 on success.150 *151 * Extracted from152 *153 * WORKING X3T9.2154 * DRAFT 792D155 * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf156 *157 * Revision 6158 * 10-MAR-94159 * Information technology -160 * SCSI-2 Common access method161 * transport and SCSI interface module162 * 163 * ANNEX A :164 *165 * setsize() converts a read capacity value to int 13h166 * head-cylinder-sector requirements. It minimizes the value for167 * number of heads and maximizes the number of cylinders. This168 * will support rather large disks before the number of heads169 * will not fit in 4 bits (or 6 bits). This algorithm also170 * minimizes the number of sectors that will be unused at the end171 * of the disk while allowing for very large disks to be172 * accommodated. This algorithm does not use physical geometry. 173 */174 175static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,176 unsigned int *secs)177{178 unsigned int rv = 0;179 unsigned long heads, sectors, cylinders, temp;180 181 cylinders = 1024L; /* Set number of cylinders to max */182 sectors = 62L; /* Maximize sectors per track */183 184 temp = cylinders * sectors; /* Compute divisor for heads */185 heads = capacity / temp; /* Compute value for number of heads */186 if (capacity % temp) { /* If no remainder, done! */187 heads++; /* Else, increment number of heads */188 temp = cylinders * heads; /* Compute divisor for sectors */189 sectors = capacity / temp; /* Compute value for sectors per190 track */191 if (capacity % temp) { /* If no remainder, done! */192 sectors++; /* Else, increment number of sectors */193 temp = heads * sectors; /* Compute divisor for cylinders */194 cylinders = capacity / temp; /* Compute number of cylinders */195 }196 }197 if (cylinders == 0)198 rv = (unsigned) -1; /* Give error if 0 cylinders */199 200 *cyls = (unsigned int) cylinders; /* Stuff return values */201 *secs = (unsigned int) sectors;202 *hds = (unsigned int) heads;203 return (rv);204}205 206/**207 * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors.208 * @bdev: which device209 * @capacity: size of the disk in sectors210 * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders211 *212 * Description : determine the BIOS mapping/geometry used for a drive in a213 * SCSI-CAM system, storing the results in ip as required214 * by the HDIO_GETGEO ioctl().215 *216 * Returns : -1 on failure, 0 on success.217 */218int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip)219{220 u64 capacity64 = capacity; /* Suppress gcc warning */221 int ret = 0;222 223 /* try to infer mapping from partition table */224 if (scsi_partsize(bdev, capacity, ip))225 return 0;226 227 if (capacity64 < (1ULL << 32)) {228 /*229 * Pick some standard mapping with at most 1024 cylinders, and230 * at most 62 sectors per track - this works up to 7905 MB.231 */232 ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,233 (unsigned int *)ip + 0, (unsigned int *)ip + 1);234 }235 236 /*237 * If something went wrong, then apparently we have to return a geometry238 * with more than 1024 cylinders.239 */240 if (ret || ip[0] > 255 || ip[1] > 63) {241 if ((capacity >> 11) > 65534) {242 ip[0] = 255;243 ip[1] = 63;244 } else {245 ip[0] = 64;246 ip[1] = 32;247 }248 249 if (capacity > 65535*63*255)250 ip[2] = 65535;251 else252 ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);253 }254 255 return 0;256}257EXPORT_SYMBOL(scsicam_bios_param);258