linux/drivers/scsi/scsicam.c
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   1/*
   2 * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc.
   3 *
   4 * Copyright 1993, 1994 Drew Eckhardt
   5 *      Visionary Computing 
   6 *      (Unix and Linux consulting and custom programming)
   7 *      drew@Colorado.EDU
   8 *      +1 (303) 786-7975
   9 *
  10 * For more information, please consult the SCSI-CAM draft.
  11 */
  12
  13#include <linux/module.h>
  14#include <linux/slab.h>
  15#include <linux/fs.h>
  16#include <linux/genhd.h>
  17#include <linux/kernel.h>
  18#include <linux/blkdev.h>
  19#include <asm/unaligned.h>
  20
  21#include <scsi/scsicam.h>
  22
  23
  24static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
  25                   unsigned int *secs);
  26
  27/**
  28 * scsi_bios_ptable - Read PC partition table out of first sector of device.
  29 * @dev: from this device
  30 *
  31 * Description: Reads the first sector from the device and returns %0x42 bytes
  32 *              starting at offset %0x1be.
  33 * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error.
  34 */
  35unsigned char *scsi_bios_ptable(struct block_device *dev)
  36{
  37        unsigned char *res = kmalloc(66, GFP_KERNEL);
  38        if (res) {
  39                struct block_device *bdev = dev->bd_contains;
  40                Sector sect;
  41                void *data = read_dev_sector(bdev, 0, &sect);
  42                if (data) {
  43                        memcpy(res, data + 0x1be, 66);
  44                        put_dev_sector(sect);
  45                } else {
  46                        kfree(res);
  47                        res = NULL;
  48                }
  49        }
  50        return res;
  51}
  52EXPORT_SYMBOL(scsi_bios_ptable);
  53
  54/**
  55 * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors.
  56 * @bdev: which device
  57 * @capacity: size of the disk in sectors
  58 * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders
  59 *
  60 * Description : determine the BIOS mapping/geometry used for a drive in a
  61 *      SCSI-CAM system, storing the results in ip as required
  62 *      by the HDIO_GETGEO ioctl().
  63 *
  64 * Returns : -1 on failure, 0 on success.
  65 */
  66
  67int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip)
  68{
  69        unsigned char *p;
  70        u64 capacity64 = capacity;      /* Suppress gcc warning */
  71        int ret;
  72
  73        p = scsi_bios_ptable(bdev);
  74        if (!p)
  75                return -1;
  76
  77        /* try to infer mapping from partition table */
  78        ret = scsi_partsize(p, (unsigned long)capacity, (unsigned int *)ip + 2,
  79                               (unsigned int *)ip + 0, (unsigned int *)ip + 1);
  80        kfree(p);
  81
  82        if (ret == -1 && capacity64 < (1ULL << 32)) {
  83                /* pick some standard mapping with at most 1024 cylinders,
  84                   and at most 62 sectors per track - this works up to
  85                   7905 MB */
  86                ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,
  87                       (unsigned int *)ip + 0, (unsigned int *)ip + 1);
  88        }
  89
  90        /* if something went wrong, then apparently we have to return
  91           a geometry with more than 1024 cylinders */
  92        if (ret || ip[0] > 255 || ip[1] > 63) {
  93                if ((capacity >> 11) > 65534) {
  94                        ip[0] = 255;
  95                        ip[1] = 63;
  96                } else {
  97                        ip[0] = 64;
  98                        ip[1] = 32;
  99                }
 100
 101                if (capacity > 65535*63*255)
 102                        ip[2] = 65535;
 103                else
 104                        ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
 105        }
 106
 107        return 0;
 108}
 109EXPORT_SYMBOL(scsicam_bios_param);
 110
 111/**
 112 * scsi_partsize - Parse cylinders/heads/sectors from PC partition table
 113 * @buf: partition table, see scsi_bios_ptable()
 114 * @capacity: size of the disk in sectors
 115 * @cyls: put cylinders here
 116 * @hds: put heads here
 117 * @secs: put sectors here
 118 *
 119 * Description: determine the BIOS mapping/geometry used to create the partition
 120 *      table, storing the results in *cyls, *hds, and *secs 
 121 *
 122 * Returns: -1 on failure, 0 on success.
 123 */
 124
 125int scsi_partsize(unsigned char *buf, unsigned long capacity,
 126               unsigned int *cyls, unsigned int *hds, unsigned int *secs)
 127{
 128        struct partition *p = (struct partition *)buf, *largest = NULL;
 129        int i, largest_cyl;
 130        int cyl, ext_cyl, end_head, end_cyl, end_sector;
 131        unsigned int logical_end, physical_end, ext_physical_end;
 132
 133
 134        if (*(unsigned short *) (buf + 64) == 0xAA55) {
 135                for (largest_cyl = -1, i = 0; i < 4; ++i, ++p) {
 136                        if (!p->sys_ind)
 137                                continue;
 138#ifdef DEBUG
 139                        printk("scsicam_bios_param : partition %d has system \n",
 140                               i);
 141#endif
 142                        cyl = p->cyl + ((p->sector & 0xc0) << 2);
 143                        if (cyl > largest_cyl) {
 144                                largest_cyl = cyl;
 145                                largest = p;
 146                        }
 147                }
 148        }
 149        if (largest) {
 150                end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);
 151                end_head = largest->end_head;
 152                end_sector = largest->end_sector & 0x3f;
 153
 154                if (end_head + 1 == 0 || end_sector == 0)
 155                        return -1;
 156
 157#ifdef DEBUG
 158                printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
 159                       end_head, end_cyl, end_sector);
 160#endif
 161
 162                physical_end = end_cyl * (end_head + 1) * end_sector +
 163                    end_head * end_sector + end_sector;
 164
 165                /* This is the actual _sector_ number at the end */
 166                logical_end = get_unaligned(&largest->start_sect)
 167                    + get_unaligned(&largest->nr_sects);
 168
 169                /* This is for >1023 cylinders */
 170                ext_cyl = (logical_end - (end_head * end_sector + end_sector))
 171                    / (end_head + 1) / end_sector;
 172                ext_physical_end = ext_cyl * (end_head + 1) * end_sector +
 173                    end_head * end_sector + end_sector;
 174
 175#ifdef DEBUG
 176                printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n"
 177                  ,logical_end, physical_end, ext_physical_end, ext_cyl);
 178#endif
 179
 180                if ((logical_end == physical_end) ||
 181                  (end_cyl == 1023 && ext_physical_end == logical_end)) {
 182                        *secs = end_sector;
 183                        *hds = end_head + 1;
 184                        *cyls = capacity / ((end_head + 1) * end_sector);
 185                        return 0;
 186                }
 187#ifdef DEBUG
 188                printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
 189                       logical_end, physical_end);
 190#endif
 191        }
 192        return -1;
 193}
 194EXPORT_SYMBOL(scsi_partsize);
 195
 196/*
 197 * Function : static int setsize(unsigned long capacity,unsigned int *cyls,
 198 *      unsigned int *hds, unsigned int *secs);
 199 *
 200 * Purpose : to determine a near-optimal int 0x13 mapping for a
 201 *      SCSI disk in terms of lost space of size capacity, storing
 202 *      the results in *cyls, *hds, and *secs.
 203 *
 204 * Returns : -1 on failure, 0 on success.
 205 *
 206 * Extracted from
 207 *
 208 * WORKING                                                    X3T9.2
 209 * DRAFT                                                        792D
 210 * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
 211 *
 212 *                                                        Revision 6
 213 *                                                         10-MAR-94
 214 * Information technology -
 215 * SCSI-2 Common access method
 216 * transport and SCSI interface module
 217 * 
 218 * ANNEX A :
 219 *
 220 * setsize() converts a read capacity value to int 13h
 221 * head-cylinder-sector requirements. It minimizes the value for
 222 * number of heads and maximizes the number of cylinders. This
 223 * will support rather large disks before the number of heads
 224 * will not fit in 4 bits (or 6 bits). This algorithm also
 225 * minimizes the number of sectors that will be unused at the end
 226 * of the disk while allowing for very large disks to be
 227 * accommodated. This algorithm does not use physical geometry. 
 228 */
 229
 230static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
 231                   unsigned int *secs)
 232{
 233        unsigned int rv = 0;
 234        unsigned long heads, sectors, cylinders, temp;
 235
 236        cylinders = 1024L;      /* Set number of cylinders to max */
 237        sectors = 62L;          /* Maximize sectors per track */
 238
 239        temp = cylinders * sectors;     /* Compute divisor for heads */
 240        heads = capacity / temp;        /* Compute value for number of heads */
 241        if (capacity % temp) {  /* If no remainder, done! */
 242                heads++;        /* Else, increment number of heads */
 243                temp = cylinders * heads;       /* Compute divisor for sectors */
 244                sectors = capacity / temp;      /* Compute value for sectors per
 245                                                   track */
 246                if (capacity % temp) {  /* If no remainder, done! */
 247                        sectors++;      /* Else, increment number of sectors */
 248                        temp = heads * sectors;         /* Compute divisor for cylinders */
 249                        cylinders = capacity / temp;    /* Compute number of cylinders */
 250                }
 251        }
 252        if (cylinders == 0)
 253                rv = (unsigned) -1;     /* Give error if 0 cylinders */
 254
 255        *cyls = (unsigned int) cylinders;       /* Stuff return values */
 256        *secs = (unsigned int) sectors;
 257        *hds = (unsigned int) heads;
 258        return (rv);
 259}
 260
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