/*
   * 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 <linux/buffer_head.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

   *

   * Description: 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 
  ",
  			       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
  ",
  		       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
  "
  		  ,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)
  ",
  		       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);
  }