drivers/scsi/scsicam.c

   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/fs.h>
  15 #include <linux/genhd.h>
  16 #include <linux/kernel.h>
  17 #include <linux/blkdev.h>
  18 #include <linux/buffer_head.h>
  19 #include <asm/unaligned.h>
  20
  21 #include <scsi/scsicam.h>
  22
  23
  24 static 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  */
  35 unsigned 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 }
  52 EXPORT_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
  67 int 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 }
 109 EXPORT_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
 125 int 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 }
 194 EXPORT_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
 230 static 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 }