drivers/scsi/scsicam.c

   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
  25 static 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  */
  36 unsigned 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 }
  53 EXPORT_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
  68 int 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 }
 110 EXPORT_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
 126 int 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 }
 195 EXPORT_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
 231 static 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 }