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/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 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 */
33unsigned char *scsi_bios_ptable(struct gendisk *dev)
34{
35 struct address_space *mapping = dev->part0->bd_mapping;
36 unsigned char *res = NULL;
37 struct folio *folio;
38
39 folio = read_mapping_folio(mapping, index: 0, NULL);
40 if (IS_ERR(ptr: 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 table
51 * @disk: gendisk of the disk to parse
52 * @capacity: size of the disk in sectors
53 * @geom: output in form of [hds, cylinders, sectors]
54 *
55 * Determine the BIOS mapping/geometry used to create the partition
56 * table, storing the results in @geom.
57 *
58 * Returns: %false on failure, %true on success.
59 */
60bool scsi_partsize(struct gendisk *disk, 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(disk);
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 DEBUG
79 printk("scsicam_bios_param : partition %d has system \n",
80 i);
81#endif
82 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 DEBUG
98 printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
99 end_head, end_cyl, end_sector);
100#endif
101
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(p: &largest->start_sect)
107 + get_unaligned_le32(p: &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 DEBUG
116 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#endif
119
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 DEBUG
130 printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
131 logical_end, physical_end);
132#endif
133 }
134
135out_free_buf:
136 kfree(objp: 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 a
146 * SCSI disk in terms of lost space of size capacity, storing
147 * the results in *cyls, *hds, and *secs.
148 *
149 * Returns : -1 on failure, 0 on success.
150 *
151 * Extracted from
152 *
153 * WORKING X3T9.2
154 * DRAFT 792D
155 * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
156 *
157 * Revision 6
158 * 10-MAR-94
159 * Information technology -
160 * SCSI-2 Common access method
161 * transport and SCSI interface module
162 *
163 * ANNEX A :
164 *
165 * setsize() converts a read capacity value to int 13h
166 * head-cylinder-sector requirements. It minimizes the value for
167 * number of heads and maximizes the number of cylinders. This
168 * will support rather large disks before the number of heads
169 * will not fit in 4 bits (or 6 bits). This algorithm also
170 * minimizes the number of sectors that will be unused at the end
171 * of the disk while allowing for very large disks to be
172 * 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 per
190 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 * @disk: which device
209 * @capacity: size of the disk in sectors
210 * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders
211 *
212 * Description : determine the BIOS mapping/geometry used for a drive in a
213 * SCSI-CAM system, storing the results in ip as required
214 * by the HDIO_GETGEO ioctl().
215 *
216 * Returns : -1 on failure, 0 on success.
217 */
218int scsicam_bios_param(struct gendisk *disk, 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(disk, capacity, ip))
225 return 0;
226
227 if (capacity64 < (1ULL << 32)) {
228 /*
229 * Pick some standard mapping with at most 1024 cylinders, and
230 * at most 62 sectors per track - this works up to 7905 MB.
231 */
232 ret = setsize(capacity: (unsigned long)capacity, cyls: (unsigned int *)ip + 2,
233 hds: (unsigned int *)ip + 0, secs: (unsigned int *)ip + 1);
234 }
235
236 /*
237 * If something went wrong, then apparently we have to return a geometry
238 * 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 else
252 ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
253 }
254
255 return 0;
256}
257EXPORT_SYMBOL(scsicam_bios_param);
258