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