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
25static 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 */
36unsigned 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, &sect);
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}
53EXPORT_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
68int 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}
110EXPORT_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
126int 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}
195EXPORT_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
231static 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