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/slab.h>
15 #include <linux/fs.h>
16 #include <linux/genhd.h>
17 #include <linux/kernel.h>
18 #include <linux/blkdev.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  */
scsi_bios_ptable(struct block_device * dev)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 
scsicam_bios_param(struct block_device * bdev,sector_t capacity,int * ip)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 
scsi_partsize(unsigned char * buf,unsigned long capacity,unsigned int * cyls,unsigned int * hds,unsigned int * secs)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 
setsize(unsigned long capacity,unsigned int * cyls,unsigned int * hds,unsigned int * secs)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 }
260