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

/*
 * With each packet command, we allocate a buffer of IDETAPE_PC_BUFFER_SIZE
 * bytes. This is used for several packet commands (Not for READ/WRITE commands)
 */
#define IDETAPE_PC_BUFFER_SIZE		256

/*
 * Some drives (for example, Seagate STT3401A Travan) require a very long
 * timeout, because they don't return an interrupt or clear their busy bit
 * until after the command completes (even retension commands).
 */
#define IDETAPE_WAIT_CMD		(900*HZ)

/*
 * 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),
};

struct idetape_bh {
	u32 b_size;
	atomic_t b_count;
	struct idetape_bh *b_reqnext;
	char *b_data;
};

/* 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

/*
 * Special requests for our block device strategy routine.
 *
 * In order to service a character device command, we add special requests to
 * the tail of our block device request queue and wait for their completion.
 */

enum {
	REQ_IDETAPE_PC1		= (1 << 0), /* packet command (first stage) */
	REQ_IDETAPE_PC2		= (1 << 1), /* packet command (second stage) */
	REQ_IDETAPE_READ	= (1 << 2),
	REQ_IDETAPE_WRITE	= (1 << 3),
};

/* Error codes returned in rq->errors to the higher part of the driver. */
#define IDETAPE_ERROR_GENERAL		101
#define IDETAPE_ERROR_FILEMARK		102
#define IDETAPE_ERROR_EOD		103

/* 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;
	ide_driver_t	*driver;
	struct gendisk	*disk;
	struct kref	kref;

	/*
	 *	pc points to the current processed packet command.
	 *
	 *	failed_pc points to the last failed packet command, or contains
	 *	NULL if we do not need to retry any packet command. This is
	 *	required since an additional packet command is needed before the
	 *	retry, to get detailed information on what went wrong.
	 */
	/* Current packet command */
	struct ide_atapi_pc *pc;
	/* Last failed packet command */
	struct ide_atapi_pc *failed_pc;
	/* used by REQ_IDETAPE_{READ,WRITE} requests */
	struct ide_atapi_pc queued_pc;

	struct ide_atapi_pc request_sense_pc;
	struct request request_sense_rq;

	/*
	 * 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;
	/* merge buffer */
	struct idetape_bh *merge_bh;
	/* size of the merge buffer */
	int merge_bh_size;
	/* pointer to current buffer head within the merge buffer */
	struct idetape_bh *bh;
	char *b_data;
	int b_count;

	int pages_per_buffer;
	/* Wasted space in each stage */
	int excess_bh_size;

	/* protects the ide-tape queue */
	spinlock_t lock;

	/* 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;

#define to_ide_tape(obj) container_of(obj, struct ide_tape_obj, kref)

#define ide_tape_g(disk) \
	container_of((disk)->private_data, struct ide_tape_obj, driver)

static void ide_tape_release(struct kref *);

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

	mutex_lock(&idetape_ref_mutex);
	tape = ide_tape_g(disk);
	if (tape) {
		if (ide_device_get(tape->drive))
			tape = NULL;
		else
			kref_get(&tape->kref);
	}
	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);
	kref_put(&tape->kref, ide_tape_release);
	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];

#define ide_tape_f(file) ((file)->private_data)

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)
		kref_get(&tape->kref);
	mutex_unlock(&idetape_ref_mutex);
	return tape;
}

static void idetape_input_buffers(ide_drive_t *drive, struct ide_atapi_pc *pc,
				  unsigned int bcount)
{
	struct idetape_bh *bh = pc->bh;
	int count;

	while (bcount) {
		if (bh == NULL) {
			printk(KERN_ERR "ide-tape: bh == NULL in "
				"idetape_input_buffers\n");
			ide_pad_transfer(drive, 0, bcount);
			return;
		}
		count = min(
			(unsigned int)(bh->b_size - atomic_read(&bh->b_count)),
			bcount);
		drive->hwif->tp_ops->input_data(drive, NULL, bh->b_data +
					atomic_read(&bh->b_count), count);
		bcount -= count;
		atomic_add(count, &bh->b_count);
		if (atomic_read(&bh->b_count) == bh->b_size) {
			bh = bh->b_reqnext;
			if (bh)
				atomic_set(&bh->b_count, 0);
		}
	}
	pc->bh = bh;
}

static void idetape_output_buffers(ide_drive_t *drive, struct ide_atapi_pc *pc,
				   unsigned int bcount)
{
	struct idetape_bh *bh = pc->bh;
	int count;

	while (bcount) {
		if (bh == NULL) {
			printk(KERN_ERR "ide-tape: bh == NULL in %s\n",
					__func__);
			return;
		}
		count = min((unsigned int)pc->b_count, (unsigned int)bcount);
		drive->hwif->tp_ops->output_data(drive, NULL, pc->b_data, count);
		bcount -= count;
		pc->b_data += count;
		pc->b_count -= count;
		if (!pc->b_count) {
			bh = bh->b_reqnext;
			pc->bh = bh;
			if (bh) {
				pc->b_data = bh->b_data;
				pc->b_count = atomic_read(&bh->b_count);
			}
		}
	}
}

static void idetape_update_buffers(ide_drive_t *drive, struct ide_atapi_pc *pc)
{
	struct idetape_bh *bh = pc->bh;
	int count;
	unsigned int bcount = pc->xferred;

	if (pc->flags & PC_FLAG_WRITING)
		return;
	while (bcount) {
		if (bh == NULL) {
			printk(KERN_ERR "ide-tape: bh == NULL in %s\n",
					__func__);
			return;
		}
		count = min((unsigned int)bh->b_size, (unsigned int)bcount);
		atomic_set(&bh->b_count, count);
		if (atomic_read(&bh->b_count) == bh->b_size)
			bh = bh->b_reqnext;
		bcount -= count;
	}
	pc->bh = bh;
}

/*
 * 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 = tape->failed_pc;

	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 = pc->req_xfer -
			tape->blk_size *
			get_unaligned_be32(&sense[3]);
		idetape_update_buffers(drive, pc);
	}

	/*
	 * 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 = IDETAPE_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 = IDETAPE_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 = IDETAPE_ERROR_EOD;
			pc->flags |= PC_FLAG_ABORT;
		}
		if (!(pc->flags & PC_FLAG_ABORT) &&
		    pc->xferred)
			pc->retries = IDETAPE_MAX_PC_RETRIES + 1;
	}
}

/* Free data buffers completely. */
static void ide_tape_kfree_buffer(idetape_tape_t *tape)
{
	struct idetape_bh *prev_bh, *bh = tape->merge_bh;

	while (bh) {
		u32 size = bh->b_size;

		while (size) {
			unsigned int order = fls(size >> PAGE_SHIFT)-1;

			if (bh->b_data)
				free_pages((unsigned long)bh->b_data, order);

			size &= (order-1);
			bh->b_data += (1 << order) * PAGE_SIZE;
		}
		prev_bh = bh;
		bh = bh->b_reqnext;
		kfree(prev_bh);
	}
}

static int idetape_end_request(ide_drive_t *drive, int uptodate, int nr_sects)
{
	struct request *rq = HWGROUP(drive)->rq;
	idetape_tape_t *tape = drive->driver_data;
	unsigned long flags;
	int error;

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

	switch (uptodate) {
	case 0:	error = IDETAPE_ERROR_GENERAL; break;
	case 1: error = 0; break;
	default: error = uptodate;
	}
	rq->errors = error;
	if (error)
		tape->failed_pc = NULL;

	if (!blk_special_request(rq)) {
		ide_end_request(drive, uptodate, nr_sects);
		return 0;
	}

	spin_lock_irqsave(&tape->lock, flags);

	ide_end_drive_cmd(drive, 0, 0);

	spin_unlock_irqrestore(&tape->lock, flags);
	return 0;
}

static void ide_tape_callback(ide_drive_t *drive)
{
	idetape_tape_t *tape = drive->driver_data;
	struct ide_atapi_pc *pc = tape->pc;
	int uptodate = pc->error ? 0 : 1;

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

	if (tape->failed_pc == pc)
		tape->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) {
		struct request *rq = drive->hwif->hwgroup->rq;
		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->current_nr_sectors -= blocks;

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

	idetape_end_request(drive, uptodate, 0);
}

static void idetape_init_pc(struct ide_atapi_pc *pc)
{
	memset(pc->c, 0, 12);
	pc->retries = 0;
	pc->flags = 0;
	pc->req_xfer = 0;
	pc->buf = pc->pc_buf;
	pc->buf_size = IDETAPE_PC_BUFFER_SIZE;
	pc->bh = NULL;
	pc->b_data = NULL;
}

static void idetape_create_request_sense_cmd(struct ide_atapi_pc *pc)
{
	idetape_init_pc(pc);
	pc->c[0] = REQUEST_SENSE;
	pc->c[4] = 20;
	pc->req_xfer = 20;
}

/*
 * Generate a new packet command request in front of the request queue, before
 * the current request, so that it will be processed immediately, on the next
 * pass through the driver.
 */
static void idetape_queue_pc_head(ide_drive_t *drive, struct ide_atapi_pc *pc,
				  struct request *rq)
{
	struct ide_tape_obj *tape = drive->driver_data;

	blk_rq_init(NULL, rq);
	rq->cmd_type = REQ_TYPE_SPECIAL;
	rq->cmd_flags |= REQ_PREEMPT;
	rq->buffer = (char *) pc;
	rq->rq_disk = tape->disk;
	memcpy(rq->cmd, pc->c, 12);
	rq->cmd[13] = REQ_IDETAPE_PC1;
	ide_do_drive_cmd(drive, rq);
}

/*
 *	idetape_retry_pc is called when an error was detected during the
 *	last packet command. We queue a request sense packet command in
 *	the head of the request list.
 */
static void idetape_retry_pc(ide_drive_t *drive)
{
	struct ide_tape_obj *tape = drive->driver_data;
	struct request *rq = &tape->request_sense_rq;
	struct ide_atapi_pc *pc = &tape->request_sense_pc;

	(void)ide_read_error(drive);
	idetape_create_request_sense_cmd(pc);
	set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);
	idetape_queue_pc_head(drive, pc, rq);
}

/*
 * Postpone the current request so that ide.c will be able to service requests
 * from another device on the same hwgroup 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 = HWGROUP(drive)->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);
}

static int ide_tape_io_buffers(ide_drive_t *drive, struct ide_atapi_pc *pc,
				unsigned int bcount, int write)
{
	if (write)
		idetape_output_buffers(drive, pc, bcount);
	else
		idetape_input_buffers(drive, pc, bcount);

	return bcount;
}

/*
 * This is the usual interrupt handler which will be called during a packet
 * command. We will transfer some of the data (as requested by the drive) and
 * will re-point interrupt handler to us. When data transfer is finished, we
 * will act according to the algorithm described before
 * idetape_issue_pc.
 */
static ide_startstop_t idetape_pc_intr(ide_drive_t *drive)
{
	idetape_tape_t *tape = drive->driver_data;

	return ide_pc_intr(drive, tape->pc, idetape_pc_intr, IDETAPE_WAIT_CMD,
			   NULL, idetape_update_buffers, idetape_retry_pc,
			   ide_tape_handle_dsc, ide_tape_io_buffers);
}

/*
 * Packet Command Interface
 *
 * The current Packet Command is available in tape->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. idetape_issue_pc will send the packet command to the drive, and will set
 * the interrupt handler to idetape_pc_intr.
 *
 * 2. On each interrupt, idetape_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 idetape_transfer_pc(ide_drive_t *drive)
{
	idetape_tape_t *tape = drive->driver_data;

	return ide_transfer_pc(drive, tape->pc, idetape_pc_intr,
			       IDETAPE_WAIT_CMD, NULL);
}

static ide_startstop_t idetape_issue_pc(ide_drive_t *drive,
		struct ide_atapi_pc *pc)
{
	idetape_tape_t *tape = drive->driver_data;

	if (tape->pc->c[0] == REQUEST_SENSE &&
	    pc->c[0] == REQUEST_SENSE) {
		printk(KERN_ERR "ide-tape: possible ide-tape.c bug - "
			"Two request sense in serial were issued\n");
	}

	if (tape->failed_pc == NULL && pc->c[0] != REQUEST_SENSE)
		tape->failed_pc = pc;
	/* Set the current packet command */
	tape->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 = IDETAPE_ERROR_GENERAL;
		}
		tape->failed_pc = NULL;
		drive->pc_callback(drive);
		return ide_stopped;
	}
	debug_log(DBG_SENSE, "Retry #%d, cmd = %02X\n", pc->retries, pc->c[0]);

	pc->retries++;

	return ide_issue_pc(drive, pc, idetape_transfer_pc,
			    IDETAPE_WAIT_CMD, NULL);
}

/* 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)
{
	idetape_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 = tape->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 */
			idetape_retry_pc(drive);
			return ide_stopped;
		}
		pc->error = 0;
	} else {
		pc->error = IDETAPE_ERROR_GENERAL;
		tape->failed_pc = NULL;
	}
	drive->pc_callback(drive);
	return ide_stopped;
}

static void ide_tape_create_rw_cmd(idetape_tape_t *tape,
				   struct ide_atapi_pc *pc, struct request *rq,
				   u8 opcode)
{
	struct idetape_bh *bh = (struct idetape_bh *)rq->special;
	unsigned int length = rq->current_nr_sectors;

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

	if (opcode == READ_6) {
		pc->c[0] = READ_6;
		atomic_set(&bh->b_count, 0);
	} else if (opcode == WRITE_6) {
		pc->c[0] = WRITE_6;
		pc->flags |= PC_FLAG_WRITING;
		pc->b_data = bh->b_data;
		pc->b_count = atomic_read(&bh->b_count);
	}

	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;
	u8 stat;

	debug_log(DBG_SENSE, "sector: %llu, nr_sectors: %lu,"
			" current_nr_sectors: %u\n",
			(unsigned long long)rq->sector, rq->nr_sectors,
			rq->current_nr_sectors);

	if (!blk_special_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);
		ide_end_request(drive, 0, 0);
		return ide_stopped;
	}

	/* Retry a failed packet command */
	if (tape->failed_pc && tape->pc->c[0] == REQUEST_SENSE) {
		pc = tape->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");
			idetape_end_request(drive, 0, 0);
			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->dsc_overlap && !(rq->cmd[13] & REQ_IDETAPE_PC2))
		set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);

	if (drive->post_reset == 1) {
		set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);
		drive->post_reset = 0;
	}

	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->buffer;
		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:
	return idetape_issue_pc(drive, pc);
}

/*
 * The function below uses __get_free_pages to allocate a data buffer of size
 * tape->buffer_size (or a bit more). We attempt to combine sequential pages as
 * much as possible.
 *
 * It returns a pointer to the newly allocated buffer, or NULL in case of
 * failure.
 */
static struct idetape_bh *ide_tape_kmalloc_buffer(idetape_tape_t *tape,
						  int full, int clear)
{
	struct idetape_bh *prev_bh, *bh, *merge_bh;
	int pages = tape->pages_per_buffer;
	unsigned int order, b_allocd;