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// 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, §);
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);
}
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