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 <linux/msdos_partition.h>
  21 #include <asm/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  */
  33 unsigned char *scsi_bios_ptable(struct block_device *dev)
  34 {
  35         struct address_space *mapping = bdev_whole(dev)->bd_inode->i_mapping;
  36         unsigned char *res = NULL;
  37         struct page *page;
  38
  39         page = read_mapping_page(mapping, 0, NULL);
  40         if (IS_ERR(page))
  41                 return NULL;
  42
  43         if (!PageError(page))
  44                 res = kmemdup(page_address(page) + 0x1be, 66, GFP_KERNEL);
  45         put_page(page);
  46         return res;
  47 }
  48 EXPORT_SYMBOL(scsi_bios_ptable);
  49
  50 /**
  51  * scsi_partsize - Parse cylinders/heads/sectors from PC partition table
  52  * @bdev: block device to parse
  53  * @capacity: size of the disk in sectors
  54  * @geom: output in form of [hds, cylinders, sectors]
  55  *
  56  * Determine the BIOS mapping/geometry used to create the partition
  57  * table, storing the results in @geom.
  58  *
  59  * Returns: %false on failure, %true on success.
  60  */
  61 bool scsi_partsize(struct block_device *bdev, sector_t capacity, int geom[3])
  62 {
  63         int cyl, ext_cyl, end_head, end_cyl, end_sector;
  64         unsigned int logical_end, physical_end, ext_physical_end;
  65         struct msdos_partition *p, *largest = NULL;
  66         void *buf;
  67         int ret = false;
  68
  69         buf = scsi_bios_ptable(bdev);
  70         if (!buf)
  71                 return false;
  72
  73         if (*(unsigned short *) (buf + 64) == 0xAA55) {
  74                 int largest_cyl = -1, i;
  75
  76                 for (i = 0, p = buf; i < 4; i++, p++) {
  77                         if (!p->sys_ind)
  78                                 continue;
  79 #ifdef DEBUG
  80                         printk("scsicam_bios_param : partition %d has system \n",
  81                                i);
  82 #endif
  83                         cyl = p->cyl + ((p->sector & 0xc0) << 2);
  84                         if (cyl > largest_cyl) {
  85                                 largest_cyl = cyl;
  86                                 largest = p;
  87                         }
  88                 }
  89         }
  90         if (largest) {
  91                 end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);
  92                 end_head = largest->end_head;
  93                 end_sector = largest->end_sector & 0x3f;
  94
  95                 if (end_head + 1 == 0 || end_sector == 0)
  96                         goto out_free_buf;
  97
  98 #ifdef DEBUG
  99                 printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
 100                        end_head, end_cyl, end_sector);
 101 #endif
 102
 103                 physical_end = end_cyl * (end_head + 1) * end_sector +
 104                     end_head * end_sector + end_sector;
 105
 106                 /* This is the actual _sector_ number at the end */
 107                 logical_end = get_unaligned_le32(&largest->start_sect)
 108                     + get_unaligned_le32(&largest->nr_sects);
 109
 110                 /* This is for >1023 cylinders */
 111                 ext_cyl = (logical_end - (end_head * end_sector + end_sector))
 112                     / (end_head + 1) / end_sector;
 113                 ext_physical_end = ext_cyl * (end_head + 1) * end_sector +
 114                     end_head * end_sector + end_sector;
 115
 116 #ifdef DEBUG
 117                 printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n"
 118                   ,logical_end, physical_end, ext_physical_end, ext_cyl);
 119 #endif
 120
 121                 if (logical_end == physical_end ||
 122                     (end_cyl == 1023 && ext_physical_end == logical_end)) {
 123                         geom[0] = end_head + 1;
 124                         geom[1] = end_sector;
 125                         geom[2] = (unsigned long)capacity /
 126                                 ((end_head + 1) * end_sector);
 127                         ret = true;
 128                         goto out_free_buf;
 129                 }
 130 #ifdef DEBUG
 131                 printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
 132                        logical_end, physical_end);
 133 #endif
 134         }
 135
 136 out_free_buf:
 137         kfree(buf);
 138         return ret;
 139 }
 140 EXPORT_SYMBOL(scsi_partsize);
 141
 142 /*
 143  * Function : static int setsize(unsigned long capacity,unsigned int *cyls,
 144  *      unsigned int *hds, unsigned int *secs);
 145  *
 146  * Purpose : to determine a near-optimal int 0x13 mapping for a
 147  *      SCSI disk in terms of lost space of size capacity, storing
 148  *      the results in *cyls, *hds, and *secs.
 149  *
 150  * Returns : -1 on failure, 0 on success.
 151  *
 152  * Extracted from
 153  *
 154  * WORKING                                                    X3T9.2
 155  * DRAFT                                                        792D
 156  * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
 157  *
 158  *                                                        Revision 6
 159  *                                                         10-MAR-94
 160  * Information technology -
 161  * SCSI-2 Common access method
 162  * transport and SCSI interface module
 163  *
 164  * ANNEX A :
 165  *
 166  * setsize() converts a read capacity value to int 13h
 167  * head-cylinder-sector requirements. It minimizes the value for
 168  * number of heads and maximizes the number of cylinders. This
 169  * will support rather large disks before the number of heads
 170  * will not fit in 4 bits (or 6 bits). This algorithm also
 171  * minimizes the number of sectors that will be unused at the end
 172  * of the disk while allowing for very large disks to be
 173  * accommodated. This algorithm does not use physical geometry.
 174  */
 175
 176 static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
 177                    unsigned int *secs)
 178 {
 179         unsigned int rv = 0;
 180         unsigned long heads, sectors, cylinders, temp;
 181
 182         cylinders = 1024L;      /* Set number of cylinders to max */
 183         sectors = 62L;          /* Maximize sectors per track */
 184
 185         temp = cylinders * sectors;     /* Compute divisor for heads */
 186         heads = capacity / temp;        /* Compute value for number of heads */
 187         if (capacity % temp) {  /* If no remainder, done! */
 188                 heads++;        /* Else, increment number of heads */
 189                 temp = cylinders * heads;       /* Compute divisor for sectors */
 190                 sectors = capacity / temp;      /* Compute value for sectors per
 191                                                    track */
 192                 if (capacity % temp) {  /* If no remainder, done! */
 193                         sectors++;      /* Else, increment number of sectors */
 194                         temp = heads * sectors;         /* Compute divisor for cylinders */
 195                         cylinders = capacity / temp;    /* Compute number of cylinders */
 196                 }
 197         }
 198         if (cylinders == 0)
 199                 rv = (unsigned) -1;     /* Give error if 0 cylinders */
 200
 201         *cyls = (unsigned int) cylinders;       /* Stuff return values */
 202         *secs = (unsigned int) sectors;
 203         *hds = (unsigned int) heads;
 204         return (rv);
 205 }
 206
 207 /**
 208  * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors.
 209  * @bdev: which device
 210  * @capacity: size of the disk in sectors
 211  * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders
 212  *
 213  * Description : determine the BIOS mapping/geometry used for a drive in a
 214  *      SCSI-CAM system, storing the results in ip as required
 215  *      by the HDIO_GETGEO ioctl().
 216  *
 217  * Returns : -1 on failure, 0 on success.
 218  */
 219 int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip)
 220 {
 221         u64 capacity64 = capacity;      /* Suppress gcc warning */
 222         int ret = 0;
 223
 224         /* try to infer mapping from partition table */
 225         if (scsi_partsize(bdev, capacity, ip))
 226                 return 0;
 227
 228         if (capacity64 < (1ULL << 32)) {
 229                 /*
 230                  * Pick some standard mapping with at most 1024 cylinders, and
 231                  * at most 62 sectors per track - this works up to 7905 MB.
 232                  */
 233                 ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,
 234                        (unsigned int *)ip + 0, (unsigned int *)ip + 1);
 235         }
 236
 237         /*
 238          * If something went wrong, then apparently we have to return a geometry
 239          * with more than 1024 cylinders.
 240          */
 241         if (ret || ip[0] > 255 || ip[1] > 63) {
 242                 if ((capacity >> 11) > 65534) {
 243                         ip[0] = 255;
 244                         ip[1] = 63;
 245                 } else {
 246                         ip[0] = 64;
 247                         ip[1] = 32;
 248                 }
 249
 250                 if (capacity > 65535*63*255)
 251                         ip[2] = 65535;
 252                 else
 253                         ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
 254         }
 255
 256         return 0;
 257 }
 258 EXPORT_SYMBOL(scsicam_bios_param);