xref: /dflybsd-src/sys/dev/disk/nata/ata-queue.c (revision eb67213abec698ffb555ee926f2761bcb7e95f55)

/*-
 * Copyright (c) 1998 - 2006 Søren Schmidt <sos@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer,
 *    without modification, immediately at the beginning of the file.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * $FreeBSD: src/sys/dev/ata/ata-queue.c,v 1.67 2007/01/27 21:15:58 remko Exp $
 */

#include "opt_ata.h"

#include <sys/param.h>
#include <sys/bus.h>
#include <sys/callout.h>
#include <sys/nata.h>
#include <sys/queue.h>
#include <sys/lock.h>
#include <sys/buf.h>
#include <sys/systm.h>
#include <sys/taskqueue.h>

#include "ata-all.h"
#include "ata_if.h"

/* prototypes */
static void ata_completed(void *, int);
static void ata_sort_queue(struct ata_channel *ch, struct ata_request *request);
static void atawritereorder(struct ata_channel *ch);
static char *ata_skey2str(u_int8_t);

void
ata_queue_init(struct ata_channel *ch)
{
    TAILQ_INIT(&ch->ata_queue);
    ch->reorder = 0;
    ch->transition = NULL;
}

/*
 * Rudely drop all requests queued to the channel of specified device.
 * XXX: The requests are leaked, use only in fatal case.
 */
void
ata_drop_requests(device_t dev)
{
    struct ata_channel *ch = device_get_softc(device_get_parent(dev));
    struct ata_request *request, *tmp;

    lockmgr(&ch->queue_mtx, LK_EXCLUSIVE);
    TAILQ_FOREACH_MUTABLE(request, &ch->ata_queue, chain, tmp) {
	TAILQ_REMOVE(&ch->ata_queue, request, chain);
	request->result = ENXIO;
    }
    lockmgr(&ch->queue_mtx, LK_RELEASE);
}

void
ata_queue_request(struct ata_request *request)
{
    struct ata_channel *ch;

    /* treat request as virgin (this might be an ATA_R_REQUEUE) */
    request->result = request->status = request->error = 0;

    /* check that the device is still valid */
    if (!(request->parent = device_get_parent(request->dev))) {
	request->result = ENXIO;
	if (request->callback)
	    (request->callback)(request);
	return;
    }
    ch = device_get_softc(request->parent);
    /* serialization done via state_mtx */
    callout_init_lk(&request->callout, &ch->state_mtx);
    if (!request->callback && !(request->flags & ATA_R_REQUEUE))
	lockinit(&request->done, "ataqueuerqdone", 0, 0);

    /* in ATA_STALL_QUEUE state we call HW directly */
    if ((ch->state & ATA_STALL_QUEUE) && (request->flags & ATA_R_CONTROL)) {
	lockmgr(&ch->state_mtx, LK_EXCLUSIVE);
	ch->running = request;
	if (ch->hw.begin_transaction(request) == ATA_OP_FINISHED) {
	    ch->running = NULL;
	    if (!request->callback)
		lockuninit(&request->done);
	    lockmgr(&ch->state_mtx, LK_RELEASE);
	    return;
	}
	/* interlock against interrupt */
	request->flags |= ATA_R_HWCMDQUEUED;
	lockmgr(&ch->state_mtx, LK_RELEASE);
    }
    /* otherwise put request on the locked queue at the specified location */
    else  {
	lockmgr(&ch->queue_mtx, LK_EXCLUSIVE);
	if (request->flags & ATA_R_AT_HEAD) {
	    TAILQ_INSERT_HEAD(&ch->ata_queue, request, chain);
	} else if (request->flags & ATA_R_ORDERED) {
	    ata_sort_queue(ch, request);
	} else {
	    TAILQ_INSERT_TAIL(&ch->ata_queue, request, chain);
	    ch->transition = NULL;
	}
	lockmgr(&ch->queue_mtx, LK_RELEASE);
	ATA_DEBUG_RQ(request, "queued");
	ata_start(ch->dev);
    }

    /* if this is a requeued request callback/sleep we're done */
    if (request->flags & ATA_R_REQUEUE)
	return;

    /* if this is not a callback wait until request is completed */
    if (!request->callback) {
	ATA_DEBUG_RQ(request, "wait for completion");
	if (!dumping) {
	    /* interlock against wakeup */
	    lockmgr(&request->done, LK_EXCLUSIVE);
	    /* check if the request was completed already */
	    if (!(request->flags & ATA_R_COMPLETED))
		lksleep(request, &request->done, 0, "ATA request completion "
		       "wait", request->timeout * hz * 4);
	    lockmgr(&request->done, LK_RELEASE);
	    /* check if the request was completed while sleeping */
	    if (!(request->flags & ATA_R_COMPLETED)) {
		/* apparently not */
		device_printf(request->dev, "WARNING - %s taskqueue timeout - "
			      "completing request directly\n",
			      ata_cmd2str(request));
		request->flags |= ATA_R_DANGER1;
		ata_completed(request, 0);
	    }
	}
	lockuninit(&request->done);
    }
}

int
ata_controlcmd(device_t dev, u_int8_t command, u_int16_t feature,
	       u_int64_t lba, u_int16_t count)
{
    struct ata_device *atadev = device_get_softc(dev);
    struct ata_request *request = ata_alloc_request();
    int error = ENOMEM;

    if (request) {
	request->dev = dev;
	request->u.ata.command = command;
	request->u.ata.lba = lba;
	request->u.ata.count = count;
	request->u.ata.feature = feature;
	request->flags = ATA_R_CONTROL;
	if (atadev->spindown_state) {
	    device_printf(dev, "request while spun down, starting.\n");
	    atadev->spindown_state = 0;
	    request->timeout = MAX(ATA_DEFAULT_TIMEOUT, 31);
	} else {
	    request->timeout = ATA_DEFAULT_TIMEOUT;
	}
	request->retries = 0;
	ata_queue_request(request);
	error = request->result;
	ata_free_request(request);
    }
    return error;
}

int
ata_atapicmd(device_t dev, u_int8_t *ccb, caddr_t data,
	     int count, int flags, int timeout)
{
    struct ata_request *request = ata_alloc_request();
    struct ata_device *atadev = device_get_softc(dev);
    int error = ENOMEM;

    if (request) {
	request->dev = dev;
	if ((atadev->param.config & ATA_PROTO_MASK) == ATA_PROTO_ATAPI_12)
	    bcopy(ccb, request->u.atapi.ccb, 12);
	else
	    bcopy(ccb, request->u.atapi.ccb, 16);
	request->data = data;
	request->bytecount = count;
	request->transfersize = min(request->bytecount, 65534);
	request->flags = flags | ATA_R_ATAPI;
	request->timeout = timeout;
	request->retries = 0;
	ata_queue_request(request);
	error = request->result;
	ata_free_request(request);
    }
    return error;
}

void
ata_start(device_t dev)
{
    struct ata_channel *ch = device_get_softc(dev);
    struct ata_request *request;
    struct ata_composite *cptr;
    int dependencies = 0;

    /* if we have a request on the queue try to get it running */
    lockmgr(&ch->queue_mtx, LK_EXCLUSIVE);
    if ((request = TAILQ_FIRST(&ch->ata_queue))) {

	/* we need the locking function to get the lock for this channel */
	if (ATA_LOCKING(dev, ATA_LF_LOCK) == ch->unit) {

	    /* check for composite dependencies */
	    if ((cptr = request->composite)) {
		lockmgr(&cptr->lock, LK_EXCLUSIVE);
		if ((request->flags & ATA_R_WRITE) &&
		    (cptr->wr_depend & cptr->rd_done) != cptr->wr_depend) {
		    dependencies = 1;
		}
		lockmgr(&cptr->lock, LK_RELEASE);
	    }

	    /* check we are in the right state and has no dependencies */
	    lockmgr(&ch->state_mtx, LK_EXCLUSIVE);
	    if (ch->state == ATA_IDLE && !dependencies) {
		ATA_DEBUG_RQ(request, "starting");

		if (ch->transition == request)
		    ch->transition = TAILQ_NEXT(request, chain);
		TAILQ_REMOVE(&ch->ata_queue, request, chain);
		ch->running = request;
		ch->state = ATA_ACTIVE;

		if (ch->hw.begin_transaction(request) == ATA_OP_FINISHED) {
		    ch->running = NULL;
		    ch->state = ATA_IDLE;
		    lockmgr(&ch->state_mtx, LK_RELEASE);
		    lockmgr(&ch->queue_mtx, LK_RELEASE);
		    ATA_LOCKING(dev, ATA_LF_UNLOCK);
		    ata_finish(request);
		    return;
		}

		/* interlock against interrupt */
		request->flags |= ATA_R_HWCMDQUEUED;

		if (dumping) {
		    lockmgr(&ch->state_mtx, LK_RELEASE);
		    lockmgr(&ch->queue_mtx, LK_RELEASE);
		    while (!ata_interrupt(ch))
			DELAY(10);
		    return;
		}
	    }
	    lockmgr(&ch->state_mtx, LK_RELEASE);
	}
    }
    lockmgr(&ch->queue_mtx, LK_RELEASE);
}

void
ata_finish(struct ata_request *request)
{
    struct ata_channel *ch = device_get_softc(request->parent);

    /*
     * if in ATA_STALL_QUEUE state or request has ATA_R_DIRECT flags set
     * we need to call ata_complete() directly here (no taskqueue involvement)
     */
    if (dumping ||
	(ch->state & ATA_STALL_QUEUE) || (request->flags & ATA_R_DIRECT)) {
	ATA_DEBUG_RQ(request, "finish directly");
	ata_completed(request, 0);
    }
    else {
	/* put request on the proper taskqueue for completion */
	/* XXX FreeBSD has some sort of bio_taskqueue code here */
        TASK_INIT(&request->task, 0, ata_completed, request);
	ATA_DEBUG_RQ(request, "finish taskqueue_swi_mp");
	taskqueue_enqueue(taskqueue_swi_mp, &request->task);
    }
}

static void
ata_completed(void *context, int dummy)
{
    struct ata_request *request = (struct ata_request *)context;
    struct ata_channel *ch = device_get_softc(request->parent);
    struct ata_device *atadev = device_get_softc(request->dev);
    struct ata_composite *composite;

    if (request->flags & ATA_R_DANGER2) {
	device_printf(request->dev,
		      "WARNING - %s freeing taskqueue zombie request\n",
		      ata_cmd2str(request));
	request->flags &= ~(ATA_R_DANGER1 | ATA_R_DANGER2);
	ata_free_request(request);
	return;
    }
    if (request->flags & ATA_R_DANGER1)
	request->flags |= ATA_R_DANGER2;

    ATA_DEBUG_RQ(request, "completed entered");

    /* if we had a timeout, reinit channel and deal with the falldown */
    if (request->flags & ATA_R_TIMEOUT) {
	/*
	 * if the channel is still present and
	 * reinit succeeds and
	 * the device doesn't get detached and
	 * there are retries left we reinject this request
	 */
	if (ch && !ata_reinit(ch->dev) && !request->result &&
	    (request->retries-- > 0)) {
	    if (!(request->flags & ATA_R_QUIET)) {
		device_printf(request->dev,
			      "TIMEOUT - %s retrying (%d retr%s left)",
			      ata_cmd2str(request), request->retries,
			      request->retries == 1 ? "y" : "ies");
		if (!(request->flags & (ATA_R_ATAPI | ATA_R_CONTROL)))
		    kprintf(" LBA=%ju", request->u.ata.lba);
		kprintf("\n");
	    }
	    request->flags &= ~(ATA_R_TIMEOUT | ATA_R_DEBUG);
	    request->flags |= (ATA_R_AT_HEAD | ATA_R_REQUEUE);
	    ATA_DEBUG_RQ(request, "completed reinject");
	    ata_queue_request(request);
	    return;
	}

	/* ran out of good intentions so finish with error */
	if (!request->result) {
	    if (!(request->flags & ATA_R_QUIET)) {
		if (request->dev) {
		    device_printf(request->dev, "FAILURE - %s timed out",
				  ata_cmd2str(request));
		    if (!(request->flags & (ATA_R_ATAPI | ATA_R_CONTROL)))
			kprintf(" LBA=%ju", request->u.ata.lba);
		    kprintf("\n");
		}
	    }
	    request->result = EIO;
	}
    }
    else if (!(request->flags & ATA_R_ATAPI) ){
	/* if this is a soft ECC error warn about it */
	/* XXX SOS we could do WARF here */
	if ((request->status & (ATA_S_CORR | ATA_S_ERROR)) == ATA_S_CORR) {
	    device_printf(request->dev,
			  "WARNING - %s soft error (ECC corrected)",
			  ata_cmd2str(request));
	    if (!(request->flags & (ATA_R_ATAPI | ATA_R_CONTROL)))
		kprintf(" LBA=%ju", request->u.ata.lba);
	    kprintf("\n");
	}

	/* if this is a UDMA CRC error we reinject if there are retries left */
	if (request->flags & ATA_R_DMA && request->error & ATA_E_ICRC) {
	    if (request->retries-- > 0) {
		device_printf(request->dev,
			      "WARNING - %s UDMA ICRC error (retrying request)",
			      ata_cmd2str(request));
		if (!(request->flags & (ATA_R_ATAPI | ATA_R_CONTROL)))
		    kprintf(" LBA=%ju", request->u.ata.lba);
		kprintf("\n");
		request->flags |= (ATA_R_AT_HEAD | ATA_R_REQUEUE);
		ata_queue_request(request);
		return;
	    }
	}
    }

    switch (request->flags & ATA_R_ATAPI) {

    /* ATA errors */
    default:
	if (!request->result && request->status & ATA_S_ERROR) {
	    if (!(request->flags & ATA_R_QUIET)) {
		device_printf(request->dev,
			      "FAILURE - %s status=%pb%i error=%pb%i",
			      ata_cmd2str(request),
			      "\20\10BUSY\7READY\6DMA_READY"
			      "\5DSC\4DRQ\3CORRECTABLE\2INDEX\1ERROR",
			      request->status,
			      "\20\10ICRC\7UNCORRECTABLE"
			      "\6MEDIA_CHANGED\5NID_NOT_FOUND"
			      "\4MEDIA_CHANGE_REQEST"
			      "\3ABORTED\2NO_MEDIA\1ILLEGAL_LENGTH",
			      request->error);
		if ((request->flags & ATA_R_DMA) &&
		    (request->dmastat & ATA_BMSTAT_ERROR))
		    kprintf(" dma=0x%02x", request->dmastat);
		if (!(request->flags & (ATA_R_ATAPI | ATA_R_CONTROL)))
		    kprintf(" LBA=%ju", request->u.ata.lba);
		kprintf("\n");
	    }
	    request->result = EIO;
	}
	break;

    /* ATAPI errors */
    case ATA_R_ATAPI:
	/* skip if result already set */
	if (request->result)
	    break;

	/* if we have a sensekey -> request sense from device */
	if ((request->error & ATA_E_ATAPI_SENSE_MASK) &&
	    (request->u.atapi.ccb[0] != ATAPI_REQUEST_SENSE)) {
	    static u_int8_t ccb[16] = { ATAPI_REQUEST_SENSE, 0, 0, 0,
					sizeof(struct atapi_sense),
					0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

	    request->u.atapi.saved_cmd = request->u.atapi.ccb[0];
	    bcopy(ccb, request->u.atapi.ccb, 16);
	    request->data = (caddr_t)&request->u.atapi.sense;
	    request->bytecount = sizeof(struct atapi_sense);
	    request->donecount = 0;
	    request->transfersize = sizeof(struct atapi_sense);
	    request->timeout = ATA_DEFAULT_TIMEOUT;
	    request->flags &= (ATA_R_ATAPI | ATA_R_QUIET);
	    request->flags |= (ATA_R_READ | ATA_R_AT_HEAD | ATA_R_REQUEUE);
	    ATA_DEBUG_RQ(request, "autoissue request sense");
	    ata_queue_request(request);
	    return;
	}

	switch (request->u.atapi.sense.key & ATA_SENSE_KEY_MASK) {
	case ATA_SENSE_RECOVERED_ERROR:
	    device_printf(request->dev, "WARNING - %s recovered error\n",
			  ata_cmd2str(request));
	    /* FALLTHROUGH */

	case ATA_SENSE_NO_SENSE:
	    request->result = 0;
	    break;

	case ATA_SENSE_NOT_READY:
	    request->result = EBUSY;
	    break;

	case ATA_SENSE_UNIT_ATTENTION:
	    atadev->flags |= ATA_D_MEDIA_CHANGED;
	    request->result = EIO;
	    break;

	default:
	    request->result = EIO;
	    if (request->flags & ATA_R_QUIET)
		break;

	    device_printf(request->dev,
			  "FAILURE - %s %s asc=0x%02x ascq=0x%02x ",
			  ata_cmd2str(request), ata_skey2str(
			  (request->u.atapi.sense.key & ATA_SENSE_KEY_MASK)),
			  request->u.atapi.sense.asc,
			  request->u.atapi.sense.ascq);
	    if (request->u.atapi.sense.specific & ATA_SENSE_SPEC_VALID)
		kprintf("sks=0x%02x 0x%02x 0x%02x\n",
		       request->u.atapi.sense.specific & ATA_SENSE_SPEC_MASK,
		       request->u.atapi.sense.specific1,
		       request->u.atapi.sense.specific2);
	    else
		kprintf("\n");
	}

	if ((request->u.atapi.sense.key & ATA_SENSE_KEY_MASK ?
	     request->u.atapi.sense.key & ATA_SENSE_KEY_MASK :
	     request->error))
	    request->result = EIO;
    }

    ATA_DEBUG_RQ(request, "completed callback/wakeup");

    /* if we are part of a composite operation we need to maintain progress */
    if ((composite = request->composite)) {
	int index = 0;

	lockmgr(&composite->lock, LK_EXCLUSIVE);

	/* update whats done */
	if (request->flags & ATA_R_READ)
	    composite->rd_done |= (1 << request->this);
	if (request->flags & ATA_R_WRITE)
	    composite->wr_done |= (1 << request->this);

	/* find ready to go dependencies */
	if (composite->wr_depend &&
	    (composite->rd_done & composite->wr_depend)==composite->wr_depend &&
	    (composite->wr_needed & (~composite->wr_done))) {
	    index = composite->wr_needed & ~composite->wr_done;
	}

	lockmgr(&composite->lock, LK_RELEASE);

	/* if we have any ready candidates kick them off */
	if (index) {
	    int bit;

	    for (bit = 0; bit < MAX_COMPOSITES; bit++) {
		if (index & (1 << bit))
		    ata_start(device_get_parent(composite->request[bit]->dev));
	    }
	}
    }

    /* get results back to the initiator for this request */
    if (request->callback)
	(request->callback)(request);
    else {
	lockmgr(&request->done, LK_EXCLUSIVE);
	request->flags |= ATA_R_COMPLETED;
	lockmgr(&request->done, LK_RELEASE);
	wakeup_one(request);
    }

    /* only call ata_start if channel is present */
    if (ch)
	ata_start(ch->dev);
}

void
ata_timeout(struct ata_request *request)
{
    struct ata_channel *ch = device_get_softc(request->parent);

    /*
     * NOTE: callout acquired ch->state_mtx for us.
     */
    /*request->flags |= ATA_R_DEBUG;*/
    ATA_DEBUG_RQ(request, "timeout");

    /*
     * if we have an ATA_ACTIVE request running, we flag the request
     * ATA_R_TIMEOUT so ata_finish will handle it correctly
     * also NULL out the running request so we wont loose
     * the race with an eventual interrupt arriving late
     */
    if (ch->state == ATA_ACTIVE) {
	request->flags |= ATA_R_TIMEOUT;
	lockmgr(&ch->state_mtx, LK_RELEASE);
	ATA_LOCKING(ch->dev, ATA_LF_UNLOCK);
	ata_finish(request);
	lockmgr(&ch->state_mtx, LK_EXCLUSIVE);
    }
}

void
ata_fail_requests(device_t dev)
{
    struct ata_channel *ch = device_get_softc(device_get_parent(dev));
    struct ata_request *request, *tmp;
    TAILQ_HEAD(, ata_request) fail_requests;
    TAILQ_INIT(&fail_requests);

    /* grap all channel locks to avoid races */
    lockmgr(&ch->queue_mtx, LK_EXCLUSIVE);
    lockmgr(&ch->state_mtx, LK_EXCLUSIVE);

    /* do we have any running request to care about ? */
    if ((request = ch->running) && (!dev || request->dev == dev)) {
	callout_cancel(&request->callout);
	ch->running = NULL;
	request->result = ENXIO;
	TAILQ_INSERT_TAIL(&fail_requests, request, chain);
    }

    /* fail all requests queued on this channel for device dev if !NULL */
    TAILQ_FOREACH_MUTABLE(request, &ch->ata_queue, chain, tmp) {
	if (!dev || request->dev == dev) {
	    if (ch->transition == request)
		ch->transition = TAILQ_NEXT(request, chain);
	    TAILQ_REMOVE(&ch->ata_queue, request, chain);
	    request->result = ENXIO;
	    TAILQ_INSERT_TAIL(&fail_requests, request, chain);
	}
    }

    lockmgr(&ch->state_mtx, LK_RELEASE);
    lockmgr(&ch->queue_mtx, LK_RELEASE);

    /* finish up all requests collected above */
    TAILQ_FOREACH_MUTABLE(request, &fail_requests, chain, tmp) {
        TAILQ_REMOVE(&fail_requests, request, chain);
        ata_finish(request);
    }
}

static u_int64_t
ata_get_lba(struct ata_request *request)
{
    if (request->flags & ATA_R_ATAPI) {
	switch (request->u.atapi.ccb[0]) {
	case ATAPI_READ_BIG:
	case ATAPI_WRITE_BIG:
	case ATAPI_READ_CD:
	    return (request->u.atapi.ccb[5]) | (request->u.atapi.ccb[4]<<8) |
		   (request->u.atapi.ccb[3]<<16)|(request->u.atapi.ccb[2]<<24);
	case ATAPI_READ:
	case ATAPI_WRITE:
	    return (request->u.atapi.ccb[4]) | (request->u.atapi.ccb[3]<<8) |
		   (request->u.atapi.ccb[2]<<16);
	default:
	    return 0;
	}
    }
    else
	return request->u.ata.lba;
}

/*
 * This implements exactly bioqdisksort() in the DragonFly kernel.
 * The short description is: Because megabytes and megabytes worth of
 * writes can be queued there needs to be a read-prioritization mechanism
 * or reads get completely starved out.
 */
static void
ata_sort_queue(struct ata_channel *ch, struct ata_request *request)
{
    if ((request->flags & ATA_R_WRITE) == 0) {
	if (ch->transition) {
	    /*
	     * Insert before the first write
	     */
	    TAILQ_INSERT_BEFORE(ch->transition, request, chain);
	    if (++ch->reorder >= bioq_reorder_minor_interval) {
		ch->reorder = 0;
		atawritereorder(ch);
	    }
	} else {
	    /*
	     * No writes queued (or ordering was forced),
	     * insert at tail.
	     */
	    TAILQ_INSERT_TAIL(&ch->ata_queue, request, chain);
	}
    } else {
	/*
	 * Writes are always appended.  If no writes were previously
	 * queued or an ordered tail insertion occured the transition
	 * field will be NULL.
	 */
	TAILQ_INSERT_TAIL(&ch->ata_queue, request, chain);
	if (ch->transition == NULL)
		ch->transition = request;
    }
    if (request->composite) {
	ch->transition = NULL;
	ch->reorder = 0;
    }
}

/*
 * Move the transition point to prevent reads from completely
 * starving our writes.  This brings a number of writes into
 * the fold every N reads.
 */
static void
atawritereorder(struct ata_channel *ch)
{
    struct ata_request *req;
    u_int64_t next_offset;
    size_t left = (size_t)bioq_reorder_minor_bytes;
    size_t n;

    next_offset = ata_get_lba(ch->transition);
    while ((req = ch->transition) != NULL &&
	   next_offset == ata_get_lba(req)) {
	n = req->u.ata.count;
	next_offset = ata_get_lba(req);
	ch->transition = TAILQ_NEXT(req, chain);
	if (left < n)
	    break;
	left -= n;
    }
}

const char *
ata_cmd2str(struct ata_request *request)
{
    static char buffer[20];

    if (request->flags & ATA_R_ATAPI) {
	switch (request->u.atapi.sense.key ?
		request->u.atapi.saved_cmd : request->u.atapi.ccb[0]) {
	case 0x00: return ("TEST_UNIT_READY");
	case 0x01: return ("REZERO");
	case 0x03: return ("REQUEST_SENSE");
	case 0x04: return ("FORMAT");
	case 0x08: return ("READ");
	case 0x0a: return ("WRITE");
	case 0x10: return ("WEOF");
	case 0x11: return ("SPACE");
	case 0x12: return ("INQUIRY");
	case 0x15: return ("MODE_SELECT");
	case 0x19: return ("ERASE");
	case 0x1a: return ("MODE_SENSE");
	case 0x1b: return ("START_STOP");
	case 0x1e: return ("PREVENT_ALLOW");
	case 0x23: return ("ATAPI_READ_FORMAT_CAPACITIES");
	case 0x25: return ("READ_CAPACITY");
	case 0x28: return ("READ_BIG");
	case 0x2a: return ("WRITE_BIG");
	case 0x2b: return ("LOCATE");
	case 0x34: return ("READ_POSITION");
	case 0x35: return ("SYNCHRONIZE_CACHE");
	case 0x3b: return ("WRITE_BUFFER");
	case 0x3c: return ("READ_BUFFER");
	case 0x42: return ("READ_SUBCHANNEL");
	case 0x43: return ("READ_TOC");
	case 0x45: return ("PLAY_10");
	case 0x47: return ("PLAY_MSF");
	case 0x48: return ("PLAY_TRACK");
	case 0x4b: return ("PAUSE");
	case 0x51: return ("READ_DISK_INFO");
	case 0x52: return ("READ_TRACK_INFO");
	case 0x53: return ("RESERVE_TRACK");
	case 0x54: return ("SEND_OPC_INFO");
	case 0x55: return ("MODE_SELECT_BIG");
	case 0x58: return ("REPAIR_TRACK");
	case 0x59: return ("READ_MASTER_CUE");
	case 0x5a: return ("MODE_SENSE_BIG");
	case 0x5b: return ("CLOSE_TRACK/SESSION");
	case 0x5c: return ("READ_BUFFER_CAPACITY");
	case 0x5d: return ("SEND_CUE_SHEET");
	case 0x96: return ("READ_CAPACITY_16");
	case 0xa1: return ("BLANK_CMD");
	case 0xa3: return ("SEND_KEY");
	case 0xa4: return ("REPORT_KEY");
	case 0xa5: return ("PLAY_12");
	case 0xa6: return ("LOAD_UNLOAD");
	case 0xad: return ("READ_DVD_STRUCTURE");
	case 0xb4: return ("PLAY_CD");
	case 0xbb: return ("SET_SPEED");
	case 0xbd: return ("MECH_STATUS");
	case 0xbe: return ("READ_CD");
	case 0xff: return ("POLL_DSC");
	}
    }
    else {
	switch (request->u.ata.command) {
	case 0x00: return ("NOP");
	case 0x08: return ("DEVICE_RESET");
	case 0x20: return ("READ");
	case 0x24: return ("READ48");
	case 0x25: return ("READ_DMA48");
	case 0x26: return ("READ_DMA_QUEUED48");
	case 0x27: return ("READ_NATIVE_MAX_ADDRESS48");
	case 0x29: return ("READ_MUL48");
	case 0x30: return ("WRITE");
	case 0x34: return ("WRITE48");
	case 0x35: return ("WRITE_DMA48");
	case 0x36: return ("WRITE_DMA_QUEUED48");
	case 0x39: return ("WRITE_MUL48");
	case 0x70: return ("SEEK");
	case 0xa0: return ("PACKET_CMD");
	case 0xa1: return ("ATAPI_IDENTIFY");
	case 0xa2: return ("SERVICE");
	case 0xb0: return ("SMART");
	case 0xc0: return ("CFA ERASE");
	case 0xc4: return ("READ_MUL");
	case 0xc5: return ("WRITE_MUL");
	case 0xc6: return ("SET_MULTI");
	case 0xc7: return ("READ_DMA_QUEUED");
	case 0xc8: return ("READ_DMA");
	case 0xca: return ("WRITE_DMA");
	case 0xcc: return ("WRITE_DMA_QUEUED");
	case 0xe6: return ("SLEEP");
	case 0xe7: return ("FLUSHCACHE");
	case 0xea: return ("FLUSHCACHE48");
	case 0xec: return ("ATA_IDENTIFY");
	case 0xef:
	    switch (request->u.ata.feature) {
	    case 0x03: return ("SETFEATURES SET TRANSFER MODE");
	    case 0x02: return ("SETFEATURES ENABLE WCACHE");
	    case 0x82: return ("SETFEATURES DISABLE WCACHE");
	    case 0xaa: return ("SETFEATURES ENABLE RCACHE");
	    case 0x55: return ("SETFEATURES DISABLE RCACHE");
	    }
	    ksprintf(buffer, "SETFEATURES 0x%02x", request->u.ata.feature);
	    return buffer;
	case 0xf8: return ("READ_NATIVE_MAX_ADDRESS");
	}
    }
    ksprintf(buffer, "unknown CMD (0x%02x)", request->u.ata.command);
    return buffer;
}

static char *
ata_skey2str(u_int8_t skey)
{
    switch (skey) {
    case 0x00: return ("NO SENSE");
    case 0x01: return ("RECOVERED ERROR");
    case 0x02: return ("NOT READY");
    case 0x03: return ("MEDIUM ERROR");
    case 0x04: return ("HARDWARE ERROR");
    case 0x05: return ("ILLEGAL REQUEST");
    case 0x06: return ("UNIT ATTENTION");
    case 0x07: return ("DATA PROTECT");
    case 0x08: return ("BLANK CHECK");
    case 0x09: return ("VENDOR SPECIFIC");
    case 0x0a: return ("COPY ABORTED");
    case 0x0b: return ("ABORTED COMMAND");
    case 0x0c: return ("EQUAL");
    case 0x0d: return ("VOLUME OVERFLOW");
    case 0x0e: return ("MISCOMPARE");
    case 0x0f: return ("RESERVED");
    default: return("UNKNOWN");
    }
}