ide-tape.c

/*
 * IDE ATAPI streaming tape driver.
 *
 * Copyright (C) 1995-1999  Gadi Oxman <gadio@netvision.net.il>
 * Copyright (C) 2003-2005  Bartlomiej Zolnierkiewicz
 *
 * This driver was constructed as a student project in the software laboratory
 * of the faculty of electrical engineering in the Technion - Israel's
 * Institute Of Technology, with the guide of Avner Lottem and Dr. Ilana David.
 *
 * It is hereby placed under the terms of the GNU general public license.
 * (See linux/COPYING).
 *
 * For a historical changelog see
 * Documentation/ide/ChangeLog.ide-tape.1995-2002
 */

#define DRV_NAME "ide-tape"

#define IDETAPE_VERSION "1.20"

#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/jiffies.h>
#include <linux/major.h>
#include <linux/errno.h>
#include <linux/genhd.h>
#include <linux/slab.h>
#include <linux/pci.h>
#include <linux/ide.h>
#include <linux/smp_lock.h>
#include <linux/completion.h>
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <scsi/scsi.h>

#include <asm/byteorder.h>
#include <linux/irq.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <asm/unaligned.h>
#include <linux/mtio.h>

enum {
	/* output errors only */
	DBG_ERR =		(1 << 0),
	/* output all sense key/asc */
	DBG_SENSE =		(1 << 1),
	/* info regarding all chrdev-related procedures */
	DBG_CHRDEV =		(1 << 2),
	/* all remaining procedures */
	DBG_PROCS =		(1 << 3),
};

/* define to see debug info */
#define IDETAPE_DEBUG_LOG		0

#if IDETAPE_DEBUG_LOG
#define debug_log(lvl, fmt, args...)			\
{							\
	if (tape->debug_mask & lvl)			\
	printk(KERN_INFO "ide-tape: " fmt, ## args);	\
}
#else
#define debug_log(lvl, fmt, args...) do {} while (0)
#endif

/**************************** Tunable parameters *****************************/
/*
 * After each failed packet command we issue a request sense command and retry
 * the packet command IDETAPE_MAX_PC_RETRIES times.
 *
 * Setting IDETAPE_MAX_PC_RETRIES to 0 will disable retries.
 */
#define IDETAPE_MAX_PC_RETRIES		3

/*
 * The following parameter is used to select the point in the internal tape fifo
 * in which we will start to refill the buffer. Decreasing the following
 * parameter will improve the system's latency and interactive response, while
 * using a high value might improve system throughput.
 */
#define IDETAPE_FIFO_THRESHOLD		2

/*
 * DSC polling parameters.
 *
 * Polling for DSC (a single bit in the status register) is a very important
 * function in ide-tape. There are two cases in which we poll for DSC:
 *
 * 1. Before a read/write packet command, to ensure that we can transfer data
 * from/to the tape's data buffers, without causing an actual media access.
 * In case the tape is not ready yet, we take out our request from the device
 * request queue, so that ide.c could service requests from the other device
 * on the same interface in the meantime.
 *
 * 2. After the successful initialization of a "media access packet command",
 * which is a command that can take a long time to complete (the interval can
 * range from several seconds to even an hour). Again, we postpone our request
 * in the middle to free the bus for the other device. The polling frequency
 * here should be lower than the read/write frequency since those media access
 * commands are slow. We start from a "fast" frequency - IDETAPE_DSC_MA_FAST
 * (1 second), and if we don't receive DSC after IDETAPE_DSC_MA_THRESHOLD
 * (5 min), we switch it to a lower frequency - IDETAPE_DSC_MA_SLOW (1 min).
 *
 * We also set a timeout for the timer, in case something goes wrong. The
 * timeout should be longer then the maximum execution time of a tape operation.
 */

/* DSC timings. */
#define IDETAPE_DSC_RW_MIN		5*HZ/100	/* 50 msec */
#define IDETAPE_DSC_RW_MAX		40*HZ/100	/* 400 msec */
#define IDETAPE_DSC_RW_TIMEOUT		2*60*HZ		/* 2 minutes */
#define IDETAPE_DSC_MA_FAST		2*HZ		/* 2 seconds */
#define IDETAPE_DSC_MA_THRESHOLD	5*60*HZ		/* 5 minutes */
#define IDETAPE_DSC_MA_SLOW		30*HZ		/* 30 seconds */
#define IDETAPE_DSC_MA_TIMEOUT		2*60*60*HZ	/* 2 hours */

/*************************** End of tunable parameters ***********************/

/* tape directions */
enum {
	IDETAPE_DIR_NONE  = (1 << 0),
	IDETAPE_DIR_READ  = (1 << 1),
	IDETAPE_DIR_WRITE = (1 << 2),
};

/* Tape door status */
#define DOOR_UNLOCKED			0
#define DOOR_LOCKED			1
#define DOOR_EXPLICITLY_LOCKED		2

/* Some defines for the SPACE command */
#define IDETAPE_SPACE_OVER_FILEMARK	1
#define IDETAPE_SPACE_TO_EOD		3

/* Some defines for the LOAD UNLOAD command */
#define IDETAPE_LU_LOAD_MASK		1
#define IDETAPE_LU_RETENSION_MASK	2
#define IDETAPE_LU_EOT_MASK		4

/* Structures related to the SELECT SENSE / MODE SENSE packet commands. */
#define IDETAPE_BLOCK_DESCRIPTOR	0
#define IDETAPE_CAPABILITIES_PAGE	0x2a

/*
 * Most of our global data which we need to save even as we leave the driver due
 * to an interrupt or a timer event is stored in the struct defined below.
 */
typedef struct ide_tape_obj {
	ide_drive_t		*drive;
	struct ide_driver	*driver;
	struct gendisk		*disk;
	struct device		dev;

	/* used by REQ_IDETAPE_{READ,WRITE} requests */
	struct ide_atapi_pc queued_pc;

	/*
	 * DSC polling variables.
	 *
	 * While polling for DSC we use postponed_rq to postpone the current
	 * request so that ide.c will be able to service pending requests on the
	 * other device. Note that at most we will have only one DSC (usually
	 * data transfer) request in the device request queue.
	 */
	struct request *postponed_rq;
	/* The time in which we started polling for DSC */
	unsigned long dsc_polling_start;
	/* Timer used to poll for dsc */
	struct timer_list dsc_timer;
	/* Read/Write dsc polling frequency */
	unsigned long best_dsc_rw_freq;
	unsigned long dsc_poll_freq;
	unsigned long dsc_timeout;

	/* Read position information */
	u8 partition;
	/* Current block */
	unsigned int first_frame;

	/* Last error information */
	u8 sense_key, asc, ascq;

	/* Character device operation */
	unsigned int minor;
	/* device name */
	char name[4];
	/* Current character device data transfer direction */
	u8 chrdev_dir;

	/* tape block size, usually 512 or 1024 bytes */
	unsigned short blk_size;
	int user_bs_factor;

	/* Copy of the tape's Capabilities and Mechanical Page */
	u8 caps[20];

	/*
	 * Active data transfer request parameters.
	 *
	 * At most, there is only one ide-tape originated data transfer request
	 * in the device request queue. This allows ide.c to easily service
	 * requests from the other device when we postpone our active request.
	 */

	/* Data buffer size chosen based on the tape's recommendation */
	int buffer_size;
	/* Staging buffer of buffer_size bytes */
	void *buf;
	/* The read/write cursor */
	void *cur;
	/* The number of valid bytes in buf */
	size_t valid;

	/* Measures average tape speed */
	unsigned long avg_time;
	int avg_size;
	int avg_speed;

	/* the door is currently locked */
	int door_locked;
	/* the tape hardware is write protected */
	char drv_write_prot;
	/* the tape is write protected (hardware or opened as read-only) */
	char write_prot;

	u32 debug_mask;
} idetape_tape_t;

static DEFINE_MUTEX(idetape_ref_mutex);

static struct class *idetape_sysfs_class;

static void ide_tape_release(struct device *);

static struct ide_tape_obj *ide_tape_get(struct gendisk *disk)
{
	struct ide_tape_obj *tape = NULL;

	mutex_lock(&idetape_ref_mutex);
	tape = ide_drv_g(disk, ide_tape_obj);
	if (tape) {
		if (ide_device_get(tape->drive))
			tape = NULL;
		else
			get_device(&tape->dev);
	}
	mutex_unlock(&idetape_ref_mutex);
	return tape;
}

static void ide_tape_put(struct ide_tape_obj *tape)
{
	ide_drive_t *drive = tape->drive;

	mutex_lock(&idetape_ref_mutex);
	put_device(&tape->dev);
	ide_device_put(drive);
	mutex_unlock(&idetape_ref_mutex);
}

/*
 * The variables below are used for the character device interface. Additional
 * state variables are defined in our ide_drive_t structure.
 */
static struct ide_tape_obj *idetape_devs[MAX_HWIFS * MAX_DRIVES];

static struct ide_tape_obj *ide_tape_chrdev_get(unsigned int i)
{
	struct ide_tape_obj *tape = NULL;

	mutex_lock(&idetape_ref_mutex);
	tape = idetape_devs[i];
	if (tape)
		get_device(&tape->dev);
	mutex_unlock(&idetape_ref_mutex);
	return tape;
}

/*
 * called on each failed packet command retry to analyze the request sense. We
 * currently do not utilize this information.
 */
static void idetape_analyze_error(ide_drive_t *drive, u8 *sense)
{
	idetape_tape_t *tape = drive->driver_data;
	struct ide_atapi_pc *pc = drive->failed_pc;
	struct request *rq = drive->hwif->rq;

	tape->sense_key = sense[2] & 0xF;
	tape->asc       = sense[12];
	tape->ascq      = sense[13];

	debug_log(DBG_ERR, "pc = %x, sense key = %x, asc = %x, ascq = %x\n",
		 pc->c[0], tape->sense_key, tape->asc, tape->ascq);

	/* Correct pc->xferred by asking the tape.	 */
	if (pc->flags & PC_FLAG_DMA_ERROR)
		pc->xferred = blk_rq_bytes(rq) -
			tape->blk_size *
			get_unaligned_be32(&sense[3]);

	/*
	 * If error was the result of a zero-length read or write command,
	 * with sense key=5, asc=0x22, ascq=0, let it slide.  Some drives
	 * (i.e. Seagate STT3401A Travan) don't support 0-length read/writes.
	 */
	if ((pc->c[0] == READ_6 || pc->c[0] == WRITE_6)
	    /* length == 0 */
	    && pc->c[4] == 0 && pc->c[3] == 0 && pc->c[2] == 0) {
		if (tape->sense_key == 5) {
			/* don't report an error, everything's ok */
			pc->error = 0;
			/* don't retry read/write */
			pc->flags |= PC_FLAG_ABORT;
		}
	}
	if (pc->c[0] == READ_6 && (sense[2] & 0x80)) {
		pc->error = IDE_DRV_ERROR_FILEMARK;
		pc->flags |= PC_FLAG_ABORT;
	}
	if (pc->c[0] == WRITE_6) {
		if ((sense[2] & 0x40) || (tape->sense_key == 0xd
		     && tape->asc == 0x0 && tape->ascq == 0x2)) {
			pc->error = IDE_DRV_ERROR_EOD;
			pc->flags |= PC_FLAG_ABORT;
		}
	}
	if (pc->c[0] == READ_6 || pc->c[0] == WRITE_6) {
		if (tape->sense_key == 8) {
			pc->error = IDE_DRV_ERROR_EOD;
			pc->flags |= PC_FLAG_ABORT;
		}
		if (!(pc->flags & PC_FLAG_ABORT) &&
		    pc->xferred)
			pc->retries = IDETAPE_MAX_PC_RETRIES + 1;
	}
}

static void ide_tape_handle_dsc(ide_drive_t *);

static int ide_tape_callback(ide_drive_t *drive, int dsc)
{
	idetape_tape_t *tape = drive->driver_data;
	struct ide_atapi_pc *pc = drive->pc;
	struct request *rq = drive->hwif->rq;
	int uptodate = pc->error ? 0 : 1;
	int err = uptodate ? 0 : IDE_DRV_ERROR_GENERAL;

	debug_log(DBG_PROCS, "Enter %s\n", __func__);

	if (dsc)
		ide_tape_handle_dsc(drive);

	if (drive->failed_pc == pc)
		drive->failed_pc = NULL;

	if (pc->c[0] == REQUEST_SENSE) {
		if (uptodate)
			idetape_analyze_error(drive, pc->buf);
		else
			printk(KERN_ERR "ide-tape: Error in REQUEST SENSE "
					"itself - Aborting request!\n");
	} else if (pc->c[0] == READ_6 || pc->c[0] == WRITE_6) {
		int blocks = pc->xferred / tape->blk_size;

		tape->avg_size += blocks * tape->blk_size;

		if (time_after_eq(jiffies, tape->avg_time + HZ)) {
			tape->avg_speed = tape->avg_size * HZ /
				(jiffies - tape->avg_time) / 1024;
			tape->avg_size = 0;
			tape->avg_time = jiffies;
		}

		tape->first_frame += blocks;
		rq->resid_len = blk_rq_bytes(rq) - blocks * tape->blk_size;

		if (pc->error) {
			uptodate = 0;
			err = pc->error;
		}
	} else if (pc->c[0] == READ_POSITION && uptodate) {
		u8 *readpos = pc->buf;

		debug_log(DBG_SENSE, "BOP - %s\n",
				(readpos[0] & 0x80) ? "Yes" : "No");
		debug_log(DBG_SENSE, "EOP - %s\n",
				(readpos[0] & 0x40) ? "Yes" : "No");

		if (readpos[0] & 0x4) {
			printk(KERN_INFO "ide-tape: Block location is unknown"
					 "to the tape\n");
			clear_bit(IDE_AFLAG_ADDRESS_VALID, &drive->atapi_flags);
			uptodate = 0;
			err = IDE_DRV_ERROR_GENERAL;
		} else {
			debug_log(DBG_SENSE, "Block Location - %u\n",
					be32_to_cpup((__be32 *)&readpos[4]));

			tape->partition = readpos[1];
			tape->first_frame = be32_to_cpup((__be32 *)&readpos[4]);
			set_bit(IDE_AFLAG_ADDRESS_VALID, &drive->atapi_flags);
		}
	}

	rq->errors = err;

	return uptodate;
}

/*
 * Postpone the current request so that ide.c will be able to service requests
 * from another device on the same port while we are polling for DSC.
 */
static void idetape_postpone_request(ide_drive_t *drive)
{
	idetape_tape_t *tape = drive->driver_data;

	debug_log(DBG_PROCS, "Enter %s\n", __func__);

	tape->postponed_rq = drive->hwif->rq;

	ide_stall_queue(drive, tape->dsc_poll_freq);
}

static void ide_tape_handle_dsc(ide_drive_t *drive)
{
	idetape_tape_t *tape = drive->driver_data;

	/* Media access command */
	tape->dsc_polling_start = jiffies;
	tape->dsc_poll_freq = IDETAPE_DSC_MA_FAST;
	tape->dsc_timeout = jiffies + IDETAPE_DSC_MA_TIMEOUT;
	/* Allow ide.c to handle other requests */
	idetape_postpone_request(drive);
}

/*
 * Packet Command Interface
 *
 * The current Packet Command is available in drive->pc, and will not change
 * until we finish handling it. Each packet command is associated with a
 * callback function that will be called when the command is finished.
 *
 * The handling will be done in three stages:
 *
 * 1. ide_tape_issue_pc will send the packet command to the drive, and will set
 * the interrupt handler to ide_pc_intr.
 *
 * 2. On each interrupt, ide_pc_intr will be called. This step will be
 * repeated until the device signals us that no more interrupts will be issued.
 *
 * 3. ATAPI Tape media access commands have immediate status with a delayed
 * process. In case of a successful initiation of a media access packet command,
 * the DSC bit will be set when the actual execution of the command is finished.
 * Since the tape drive will not issue an interrupt, we have to poll for this
 * event. In this case, we define the request as "low priority request" by
 * setting rq_status to IDETAPE_RQ_POSTPONED, set a timer to poll for DSC and
 * exit the driver.
 *
 * ide.c will then give higher priority to requests which originate from the
 * other device, until will change rq_status to RQ_ACTIVE.
 *
 * 4. When the packet command is finished, it will be checked for errors.
 *
 * 5. In case an error was found, we queue a request sense packet command in
 * front of the request queue and retry the operation up to
 * IDETAPE_MAX_PC_RETRIES times.
 *
 * 6. In case no error was found, or we decided to give up and not to retry
 * again, the callback function will be called and then we will handle the next
 * request.
 */

static ide_startstop_t ide_tape_issue_pc(ide_drive_t *drive,
					 struct ide_cmd *cmd,
					 struct ide_atapi_pc *pc)
{
	idetape_tape_t *tape = drive->driver_data;
	struct request *rq = drive->hwif->rq;

	if (drive->failed_pc == NULL && pc->c[0] != REQUEST_SENSE)
		drive->failed_pc = pc;

	/* Set the current packet command */
	drive->pc = pc;

	if (pc->retries > IDETAPE_MAX_PC_RETRIES ||
		(pc->flags & PC_FLAG_ABORT)) {

		/*
		 * We will "abort" retrying a packet command in case legitimate
		 * error code was received (crossing a filemark, or end of the
		 * media, for example).
		 */
		if (!(pc->flags & PC_FLAG_ABORT)) {
			if (!(pc->c[0] == TEST_UNIT_READY &&
			      tape->sense_key == 2 && tape->asc == 4 &&
			     (tape->ascq == 1 || tape->ascq == 8))) {
				printk(KERN_ERR "ide-tape: %s: I/O error, "
						"pc = %2x, key = %2x, "
						"asc = %2x, ascq = %2x\n",
						tape->name, pc->c[0],
						tape->sense_key, tape->asc,
						tape->ascq);
			}
			/* Giving up */
			pc->error = IDE_DRV_ERROR_GENERAL;
		}

		drive->failed_pc = NULL;
		drive->pc_callback(drive, 0);
		ide_complete_rq(drive, -EIO, blk_rq_bytes(rq));
		return ide_stopped;
	}
	debug_log(DBG_SENSE, "Retry #%d, cmd = %02X\n", pc->retries, pc->c[0]);

	pc->retries++;

	return ide_issue_pc(drive, cmd);
}

/* A mode sense command is used to "sense" tape parameters. */
static void idetape_create_mode_sense_cmd(struct ide_atapi_pc *pc, u8 page_code)
{
	ide_init_pc(pc);
	pc->c[0] = MODE_SENSE;
	if (page_code != IDETAPE_BLOCK_DESCRIPTOR)
		/* DBD = 1 - Don't return block descriptors */
		pc->c[1] = 8;
	pc->c[2] = page_code;
	/*
	 * Changed pc->c[3] to 0 (255 will at best return unused info).
	 *
	 * For SCSI this byte is defined as subpage instead of high byte
	 * of length and some IDE drives seem to interpret it this way
	 * and return an error when 255 is used.
	 */
	pc->c[3] = 0;
	/* We will just discard data in that case */
	pc->c[4] = 255;
	if (page_code == IDETAPE_BLOCK_DESCRIPTOR)
		pc->req_xfer = 12;
	else if (page_code == IDETAPE_CAPABILITIES_PAGE)
		pc->req_xfer = 24;
	else
		pc->req_xfer = 50;
}

static ide_startstop_t idetape_media_access_finished(ide_drive_t *drive)
{
	ide_hwif_t *hwif = drive->hwif;
	idetape_tape_t *tape = drive->driver_data;
	struct ide_atapi_pc *pc = drive->pc;
	u8 stat;

	stat = hwif->tp_ops->read_status(hwif);

	if (stat & ATA_DSC) {
		if (stat & ATA_ERR) {
			/* Error detected */
			if (pc->c[0] != TEST_UNIT_READY)
				printk(KERN_ERR "ide-tape: %s: I/O error, ",
						tape->name);
			/* Retry operation */
			ide_retry_pc(drive);
			return ide_stopped;
		}
		pc->error = 0;
	} else {
		pc->error = IDE_DRV_ERROR_GENERAL;
		drive->failed_pc = NULL;
	}
	drive->pc_callback(drive, 0);
	return ide_stopped;
}

static void ide_tape_create_rw_cmd(idetape_tape_t *tape,
				   struct ide_atapi_pc *pc, struct request *rq,
				   u8 opcode)
{
	unsigned int length = blk_rq_sectors(rq) / (tape->blk_size >> 9);

	ide_init_pc(pc);
	put_unaligned(cpu_to_be32(length), (unsigned int *) &pc->c[1]);
	pc->c[1] = 1;
	pc->buf = NULL;
	pc->buf_size = blk_rq_bytes(rq);
	if (pc->buf_size == tape->buffer_size)
		pc->flags |= PC_FLAG_DMA_OK;

	if (opcode == READ_6)
		pc->c[0] = READ_6;
	else if (opcode == WRITE_6) {
		pc->c[0] = WRITE_6;
		pc->flags |= PC_FLAG_WRITING;
	}

	memcpy(rq->cmd, pc->c, 12);
}

static ide_startstop_t idetape_do_request(ide_drive_t *drive,
					  struct request *rq, sector_t block)
{
	ide_hwif_t *hwif = drive->hwif;
	idetape_tape_t *tape = drive->driver_data;
	struct ide_atapi_pc *pc = NULL;
	struct request *postponed_rq = tape->postponed_rq;
	struct ide_cmd cmd;
	u8 stat;

	debug_log(DBG_SENSE, "sector: %llu, nr_sectors: %u\n"
		  (unsigned long long)blk_rq_pos(rq), blk_rq_sectors(rq));

	if (!(blk_special_request(rq) || blk_sense_request(rq))) {
		/* We do not support buffer cache originated requests. */
		printk(KERN_NOTICE "ide-tape: %s: Unsupported request in "
			"request queue (%d)\n", drive->name, rq->cmd_type);
		if (blk_fs_request(rq) == 0 && rq->errors == 0)
			rq->errors = -EIO;
		ide_complete_rq(drive, -EIO, ide_rq_bytes(rq));
		return ide_stopped;
	}

	/* Retry a failed packet command */
	if (drive->failed_pc && drive->pc->c[0] == REQUEST_SENSE) {
		pc = drive->failed_pc;
		goto out;
	}

	if (postponed_rq != NULL)
		if (rq != postponed_rq) {
			printk(KERN_ERR "ide-tape: ide-tape.c bug - "
					"Two DSC requests were queued\n");
			drive->failed_pc = NULL;
			rq->errors = 0;
			ide_complete_rq(drive, 0, blk_rq_bytes(rq));
			return ide_stopped;
		}

	tape->postponed_rq = NULL;

	/*
	 * If the tape is still busy, postpone our request and service
	 * the other device meanwhile.
	 */
	stat = hwif->tp_ops->read_status(hwif);

	if ((drive->dev_flags & IDE_DFLAG_DSC_OVERLAP) == 0 &&
	    (rq->cmd[13] & REQ_IDETAPE_PC2) == 0)
		set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);

	if (drive->dev_flags & IDE_DFLAG_POST_RESET) {
		set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);
		drive->dev_flags &= ~IDE_DFLAG_POST_RESET;
	}

	if (!test_and_clear_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags) &&
	    (stat & ATA_DSC) == 0) {
		if (postponed_rq == NULL) {
			tape->dsc_polling_start = jiffies;
			tape->dsc_poll_freq = tape->best_dsc_rw_freq;
			tape->dsc_timeout = jiffies + IDETAPE_DSC_RW_TIMEOUT;
		} else if (time_after(jiffies, tape->dsc_timeout)) {
			printk(KERN_ERR "ide-tape: %s: DSC timeout\n",
				tape->name);
			if (rq->cmd[13] & REQ_IDETAPE_PC2) {
				idetape_media_access_finished(drive);
				return ide_stopped;
			} else {
				return ide_do_reset(drive);
			}
		} else if (time_after(jiffies,
					tape->dsc_polling_start +
					IDETAPE_DSC_MA_THRESHOLD))
			tape->dsc_poll_freq = IDETAPE_DSC_MA_SLOW;
		idetape_postpone_request(drive);
		return ide_stopped;
	}
	if (rq->cmd[13] & REQ_IDETAPE_READ) {
		pc = &tape->queued_pc;
		ide_tape_create_rw_cmd(tape, pc, rq, READ_6);
		goto out;
	}
	if (rq->cmd[13] & REQ_IDETAPE_WRITE) {
		pc = &tape->queued_pc;
		ide_tape_create_rw_cmd(tape, pc, rq, WRITE_6);
		goto out;
	}
	if (rq->cmd[13] & REQ_IDETAPE_PC1) {
		pc = (struct ide_atapi_pc *)rq->special;
		rq->cmd[13] &= ~(REQ_IDETAPE_PC1);
		rq->cmd[13] |= REQ_IDETAPE_PC2;
		goto out;
	}
	if (rq->cmd[13] & REQ_IDETAPE_PC2) {
		idetape_media_access_finished(drive);
		return ide_stopped;
	}
	BUG();

out:
	/* prepare sense request for this command */
	ide_prep_sense(drive, rq);

	memset(&cmd, 0, sizeof(cmd));

	if (rq_data_dir(rq))
		cmd.tf_flags |= IDE_TFLAG_WRITE;

	cmd.rq = rq;

	ide_init_sg_cmd(&cmd, blk_rq_bytes(rq));
	ide_map_sg(drive, &cmd);

	return ide_tape_issue_pc(drive, &cmd, pc);
}

/*
 * Write a filemark if write_filemark=1. Flush the device buffers without
 * writing a filemark otherwise.
 */
static void idetape_create_write_filemark_cmd(ide_drive_t *drive,
		struct ide_atapi_pc *pc, int write_filemark)
{
	ide_init_pc(pc);
	pc->c[0] = WRITE_FILEMARKS;
	pc->c[4] = write_filemark;
	pc->flags |= PC_FLAG_WAIT_FOR_DSC;
}

static int idetape_wait_ready(ide_drive_t *drive, unsigned long timeout)
{
	idetape_tape_t *tape = drive->driver_data;
	struct gendisk *disk = tape->disk;
	int load_attempted = 0;

	/* Wait for the tape to become ready */
	set_bit(IDE_AFLAG_MEDIUM_PRESENT, &drive->atapi_flags);
	timeout += jiffies;
	while (time_before(jiffies, timeout)) {
		if (ide_do_test_unit_ready(drive, disk) == 0)
			return 0;
		if ((tape->sense_key == 2 && tape->asc == 4 && tape->ascq == 2)
		    || (tape->asc == 0x3A)) {
			/* no media */
			if (load_attempted)
				return -ENOMEDIUM;
			ide_do_start_stop(drive, disk, IDETAPE_LU_LOAD_MASK);
			load_attempted = 1;
		/* not about to be ready */
		} else if (!(tape->sense_key == 2 && tape->asc == 4 &&
			     (tape->ascq == 1 || tape->ascq == 8)))
			return -EIO;
		msleep(100);
	}
	return -EIO;
}

static int idetape_flush_tape_buffers(ide_drive_t *drive)
{
	struct ide_tape_obj *tape = drive->driver_data;
	struct ide_atapi_pc pc;
	int rc;

	idetape_create_write_filemark_cmd(drive, &pc, 0);
	rc = ide_queue_pc_tail(drive, tape->disk, &pc);
	if (rc)
		return rc;
	idetape_wait_ready(drive, 60 * 5 * HZ);
	return 0;
}

static void idetape_create_read_position_cmd(struct ide_atapi_pc *pc)
{
	ide_init_pc(pc);
	pc->c[0] = READ_POSITION;
	pc->req_xfer = 20;
}

static int idetape_read_position(ide_drive_t *drive)
{
	idetape_tape_t *tape = drive->driver_data;
	struct ide_atapi_pc pc;
	int position;

	debug_log(DBG_PROCS, "Enter %s\n", __func__);

	idetape_create_read_position_cmd(&pc);
	if (ide_queue_pc_tail(drive, tape->disk, &pc))
		return -1;
	position = tape->first_frame;
	return position;
}

static void idetape_create_locate_cmd(ide_drive_t *drive,
		struct ide_atapi_pc *pc,
		unsigned int block, u8 partition, int skip)
{
	ide_init_pc(pc);
	pc->c[0] = POSITION_TO_ELEMENT;
	pc->c[1] = 2;
	put_unaligned(cpu_to_be32(block), (unsigned int *) &pc->c[3]);
	pc->c[8] = partition;
	pc->flags |= PC_FLAG_WAIT_FOR_DSC;
}

static void __ide_tape_discard_merge_buffer(ide_drive_t *drive)
{
	idetape_tape_t *tape = drive->driver_data;

	if (tape->chrdev_dir != IDETAPE_DIR_READ)
		return;

	clear_bit(IDE_AFLAG_FILEMARK, &drive->atapi_flags);
	tape->valid = 0;
	if (tape->buf != NULL) {
		kfree(tape->buf);
		tape->buf = NULL;
	}

	tape->chrdev_dir = IDETAPE_DIR_NONE;
}

/*
 * Position the tape to the requested block using the LOCATE packet command.
 * A READ POSITION command is then issued to check where we are positioned. Like
 * all higher level operations, we queue the commands at the tail of the request
 * queue and wait for their completion.
 */
static int idetape_position_tape(ide_drive_t *drive, unsigned int block,
		u8 partition, int skip)
{
	idetape_tape_t *tape = drive->driver_data;
	struct gendisk *disk = tape->disk;
	int retval;
	struct ide_atapi_pc pc;

	if (tape->chrdev_dir == IDETAPE_DIR_READ)
		__ide_tape_discard_merge_buffer(drive);
	idetape_wait_ready(drive, 60 * 5 * HZ);
	idetape_create_locate_cmd(drive, &pc, block, partition, skip);
	retval = ide_queue_pc_tail(drive, disk, &pc);
	if (retval)
		return (retval);

	idetape_create_read_position_cmd(&pc);
	return ide_queue_pc_tail(drive, disk, &pc);
}

static void ide_tape_discard_merge_buffer(ide_drive_t *drive,
					  int restore_position)
{
	idetape_tape_t *tape = drive->driver_data;
	int seek, position;

	__ide_tape_discard_merge_buffer(drive);
	if (restore_position) {
		position = idetape_read_position(drive);
		seek = position > 0 ? position : 0;
		if (idetape_position_tape(drive, seek, 0, 0)) {
			printk(KERN_INFO "ide-tape: %s: position_tape failed in"
					 " %s\n", tape->name, __func__);