drivers/scsi/scsicam.c

/*
 * 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.
 */

#define __NO_VERSION__
#include <linux/module.h>

#include <linux/fs.h>
#include <linux/genhd.h>
#include <linux/kernel.h>
#include <linux/blk.h>
#include <asm/unaligned.h>
#include "scsi.h"
#include "hosts.h"
#include "sd.h"
#include <scsi/scsicam.h>

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


/*
 * Function : int scsicam_bios_param (Disk *disk, int dev, int *ip)
 *
 * Purpose : to determine the BIOS mapping 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(Disk * disk,	/* SCSI disk */
		       kdev_t dev,	/* Device major, minor */
		  int *ip /* Heads, sectors, cylinders in that order */ )
{
	struct buffer_head *bh;
	int ret_code;
	int size = disk->capacity;
	unsigned long temp_cyl;

	if (!(bh = bread(MKDEV(MAJOR(dev), MINOR(dev)&~0xf), 0, block_size(dev))))
		return -1;

	/* try to infer mapping from partition table */
	ret_code = scsi_partsize(bh, (unsigned long) size, (unsigned int *) ip + 2,
		       (unsigned int *) ip + 0, (unsigned int *) ip + 1);
	brelse(bh);

	if (ret_code == -1) {
		/* pick some standard mapping with at most 1024 cylinders,
		   and at most 62 sectors per track - this works up to
		   7905 MB */
		ret_code = setsize((unsigned long) size, (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_code || ip[0] > 255 || ip[1] > 63) {
		ip[0] = 64;
		ip[1] = 32;
		temp_cyl = size / (ip[0] * ip[1]);
		if (temp_cyl > 65534) {
			ip[0] = 255;
			ip[1] = 63;
		}
		ip[2] = size / (ip[0] * ip[1]);
	}
	return 0;
}

/*
 * Function : static int scsi_partsize(struct buffer_head *bh, unsigned long 
 *     capacity,unsigned int *cyls, unsigned int *hds, unsigned int *secs);
 *
 * Purpose : to determine the BIOS mapping used to create the partition
 *      table, storing the results in *cyls, *hds, and *secs 
 *
 * Returns : -1 on failure, 0 on success.
 *
 */

int scsi_partsize(struct buffer_head *bh, unsigned long capacity,
	       unsigned int *cyls, unsigned int *hds, unsigned int *secs)
{
	struct partition *p, *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 *) (bh->b_data + 510) == 0xAA55) {
		for (largest_cyl = -1, p = (struct partition *)
		     (0x1BE + bh->b_data), 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;
}

/*
 * 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
 *
 *
 *                                                        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);
}