scsicam.c

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/*
 * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc.
 *
 * Copyright 1993, 1994 Drew Eckhardt
 *      Visionary Computing 
 *      (Unix and Linux consulting and custom programming)
 *      [email protected]
 *      +1 (303) 786-7975
 *
 * For more information, please consult the SCSI-CAM draft.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/genhd.h>
#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <asm/unaligned.h>

#include <scsi/scsicam.h>


static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
           unsigned int *secs);

unsigned char *scsi_bios_ptable(struct block_device *dev)
{
    unsigned char *res = kmalloc(66, GFP_KERNEL);
    if (res) {
        struct block_device *bdev = dev->bd_contains;
        Sector sect;
        void *data = read_dev_sector(bdev, 0, &sect);
        if (data) {
            memcpy(res, data + 0x1be, 66);
            put_dev_sector(sect);
        } else {
            kfree(res);
            res = NULL;
        }
    }
    return res;
}
EXPORT_SYMBOL(scsi_bios_ptable);

int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip)
{
    unsigned char *p;
    u64 capacity64 = capacity;  /* Suppress gcc warning */
    int ret;

    p = scsi_bios_ptable(bdev);
    if (!p)
        return -1;

    /* try to infer mapping from partition table */
    ret = scsi_partsize(p, (unsigned long)capacity, (unsigned int *)ip + 2,
                   (unsigned int *)ip + 0, (unsigned int *)ip + 1);
    kfree(p);

    if (ret == -1 && capacity64 < (1ULL << 32)) {
        /* pick some standard mapping with at most 1024 cylinders,
           and at most 62 sectors per track - this works up to
           7905 MB */
        ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,
               (unsigned int *)ip + 0, (unsigned int *)ip + 1);
    }

    /* if something went wrong, then apparently we have to return
       a geometry with more than 1024 cylinders */
    if (ret || ip[0] > 255 || ip[1] > 63) {
        if ((capacity >> 11) > 65534) {
            ip[0] = 255;
            ip[1] = 63;
        } else {
            ip[0] = 64;
            ip[1] = 32;
        }

        if (capacity > 65535*63*255)
            ip[2] = 65535;
        else
            ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
    }

    return 0;
}
EXPORT_SYMBOL(scsicam_bios_param);

int scsi_partsize(unsigned char *buf, unsigned long capacity,
           unsigned int *cyls, unsigned int *hds, unsigned int *secs)
{
    struct partition *p = (struct partition *)buf, *largest = NULL;
    int i, largest_cyl;
    int cyl, ext_cyl, end_head, end_cyl, end_sector;
    unsigned int logical_end, physical_end, ext_physical_end;


    if (*(unsigned short *) (buf + 64) == 0xAA55) {
        for (largest_cyl = -1, i = 0; i < 4; ++i, ++p) {
            if (!p->sys_ind)
                continue;
#ifdef DEBUG
            printk("scsicam_bios_param : partition %d has system \n",
                   i);
#endif
            cyl = p->cyl + ((p->sector & 0xc0) << 2);
            if (cyl > largest_cyl) {
                largest_cyl = cyl;
                largest = p;
            }
        }
    }
    if (largest) {
        end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);
        end_head = largest->end_head;
        end_sector = largest->end_sector & 0x3f;

        if (end_head + 1 == 0 || end_sector == 0)
            return -1;

#ifdef DEBUG
        printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
               end_head, end_cyl, end_sector);
#endif

        physical_end = end_cyl * (end_head + 1) * end_sector +
            end_head * end_sector + end_sector;

        /* This is the actual _sector_ number at the end */
        logical_end = get_unaligned(&largest->start_sect)
            + get_unaligned(&largest->nr_sects);

        /* This is for >1023 cylinders */
        ext_cyl = (logical_end - (end_head * end_sector + end_sector))
            / (end_head + 1) / end_sector;
        ext_physical_end = ext_cyl * (end_head + 1) * end_sector +
            end_head * end_sector + end_sector;

#ifdef DEBUG
        printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n"
          ,logical_end, physical_end, ext_physical_end, ext_cyl);
#endif

        if ((logical_end == physical_end) ||
          (end_cyl == 1023 && ext_physical_end == logical_end)) {
            *secs = end_sector;
            *hds = end_head + 1;
            *cyls = capacity / ((end_head + 1) * end_sector);
            return 0;
        }
#ifdef DEBUG
        printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
               logical_end, physical_end);
#endif
    }
    return -1;
}
EXPORT_SYMBOL(scsi_partsize);

/*
 * Function : static int setsize(unsigned long capacity,unsigned int *cyls,
 *      unsigned int *hds, unsigned int *secs);
 *
 * Purpose : to determine a near-optimal int 0x13 mapping for a
 *      SCSI disk in terms of lost space of size capacity, storing
 *      the results in *cyls, *hds, and *secs.
 *
 * Returns : -1 on failure, 0 on success.
 *
 * Extracted from
 *
 * WORKING                                                    X3T9.2
 * DRAFT                                                        792D
 * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
 *
 *                                                        Revision 6
 *                                                         10-MAR-94
 * Information technology -
 * SCSI-2 Common access method
 * transport and SCSI interface module
 * 
 * ANNEX A :
 *
 * setsize() converts a read capacity value to int 13h
 * head-cylinder-sector requirements. It minimizes the value for
 * number of heads and maximizes the number of cylinders. This
 * will support rather large disks before the number of heads
 * will not fit in 4 bits (or 6 bits). This algorithm also
 * minimizes the number of sectors that will be unused at the end
 * of the disk while allowing for very large disks to be
 * accommodated. This algorithm does not use physical geometry. 
 */

static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
           unsigned int *secs)
{
    unsigned int rv = 0;
    unsigned long heads, sectors, cylinders, temp;

    cylinders = 1024L;  /* Set number of cylinders to max */
    sectors = 62L;      /* Maximize sectors per track */

    temp = cylinders * sectors; /* Compute divisor for heads */
    heads = capacity / temp;    /* Compute value for number of heads */
    if (capacity % temp) {  /* If no remainder, done! */
        heads++;    /* Else, increment number of heads */
        temp = cylinders * heads;   /* Compute divisor for sectors */
        sectors = capacity / temp;  /* Compute value for sectors per
                           track */
        if (capacity % temp) {  /* If no remainder, done! */
            sectors++;  /* Else, increment number of sectors */
            temp = heads * sectors;     /* Compute divisor for cylinders */
            cylinders = capacity / temp;    /* Compute number of cylinders */
        }
    }
    if (cylinders == 0)
        rv = (unsigned) -1; /* Give error if 0 cylinders */

    *cyls = (unsigned int) cylinders;   /* Stuff return values */
    *secs = (unsigned int) sectors;
    *hds = (unsigned int) heads;
    return (rv);
}