1 // SPDX-License-Identifier: GPL-2.0
3 * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc.
5 * Copyright 1993, 1994 Drew Eckhardt
7 * (Unix and Linux consulting and custom programming)
11 * For more information, please consult the SCSI-CAM draft.
14 #include <linux/module.h>
15 #include <linux/slab.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>
24 #include <scsi/scsicam.h>
27 * scsi_bios_ptable - Read PC partition table out of first sector of device.
28 * @dev: from this device
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.
34 unsigned char *scsi_bios_ptable(struct block_device *dev)
36 struct address_space *mapping = bdev_whole(dev)->bd_inode->i_mapping;
37 unsigned char *res = NULL;
40 page = read_mapping_page(mapping, 0, NULL);
45 res = kmemdup(page_address(page) + 0x1be, 66, GFP_KERNEL);
49 EXPORT_SYMBOL(scsi_bios_ptable);
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]
57 * Determine the BIOS mapping/geometry used to create the partition
58 * table, storing the results in @geom.
60 * Returns: %false on failure, %true on success.
62 bool scsi_partsize(struct block_device *bdev, sector_t capacity, int geom[3])
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;
70 buf = scsi_bios_ptable(bdev);
74 if (*(unsigned short *) (buf + 64) == 0xAA55) {
75 int largest_cyl = -1, i;
77 for (i = 0, p = buf; i < 4; i++, p++) {
81 printk("scsicam_bios_param : partition %d has system \n",
84 cyl = p->cyl + ((p->sector & 0xc0) << 2);
85 if (cyl > largest_cyl) {
92 end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);
93 end_head = largest->end_head;
94 end_sector = largest->end_sector & 0x3f;
96 if (end_head + 1 == 0 || end_sector == 0)
100 printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
101 end_head, end_cyl, end_sector);
104 physical_end = end_cyl * (end_head + 1) * end_sector +
105 end_head * end_sector + end_sector;
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);
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;
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);
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);
132 printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
133 logical_end, physical_end);
141 EXPORT_SYMBOL(scsi_partsize);
144 * Function : static int setsize(unsigned long capacity,unsigned int *cyls,
145 * unsigned int *hds, unsigned int *secs);
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.
151 * Returns : -1 on failure, 0 on success.
157 * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
161 * Information technology -
162 * SCSI-2 Common access method
163 * transport and SCSI interface module
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.
177 static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
181 unsigned long heads, sectors, cylinders, temp;
183 cylinders = 1024L; /* Set number of cylinders to max */
184 sectors = 62L; /* Maximize sectors per track */
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
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 */
200 rv = (unsigned) -1; /* Give error if 0 cylinders */
202 *cyls = (unsigned int) cylinders; /* Stuff return values */
203 *secs = (unsigned int) sectors;
204 *hds = (unsigned int) heads;
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
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().
218 * Returns : -1 on failure, 0 on success.
220 int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip)
222 u64 capacity64 = capacity; /* Suppress gcc warning */
225 /* try to infer mapping from partition table */
226 if (scsi_partsize(bdev, capacity, ip))
229 if (capacity64 < (1ULL << 32)) {
231 * Pick some standard mapping with at most 1024 cylinders, and
232 * at most 62 sectors per track - this works up to 7905 MB.
234 ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,
235 (unsigned int *)ip + 0, (unsigned int *)ip + 1);
239 * If something went wrong, then apparently we have to return a geometry
240 * with more than 1024 cylinders.
242 if (ret || ip[0] > 255 || ip[1] > 63) {
243 if ((capacity >> 11) > 65534) {
251 if (capacity > 65535*63*255)
254 ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
259 EXPORT_SYMBOL(scsicam_bios_param);