// SPDX-License-Identifier: GPL-2.0
/*
 * 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)
 *      drew@Colorado.EDU
 *      +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);

/**
 * scsi_bios_ptable - Read PC partition table out of first sector of device.
 * @dev: from this device
 *
 * Description: Reads the first sector from the device and returns %0x42 bytes
 *              starting at offset %0x1be.
 * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error.
 */
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);

/**
 * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors.
 * @bdev: which device
 * @capacity: size of the disk in sectors
 * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders
 *
 * Description : determine the BIOS mapping/geometry used for a drive in a
 *      SCSI-CAM system, storing the results in ip as required
 *      by the HDIO_GETGEO ioctl().
 *
 * Returns : -1 on failure, 0 on success.
 */

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);

/**
 * scsi_partsize - Parse cylinders/heads/sectors from PC partition table
 * @buf: partition table, see scsi_bios_ptable()
 * @capacity: size of the disk in sectors
 * @cyls: put cylinders here
 * @hds: put heads here
 * @secs: put sectors here
 *
 * Determine the BIOS mapping/geometry used to create the partition
 * table, storing the results in @cyls, @hds, and @secs
 *
 * Returns: -1 on failure, 0 on success.
 */

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_le32(&largest->start_sect)
                    + get_unaligned_le32(&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);
}