qib_rc.c

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/*
 * Copyright (c) 2006, 2007, 2008, 2009 QLogic Corporation. All rights reserved.
 * Copyright (c) 2005, 2006 PathScale, Inc. All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - 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.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <linux/io.h>

#include "qib.h"

/* cut down ridiculously long IB macro names */
#define OP(x) IB_OPCODE_RC_##x

static void rc_timeout(unsigned long arg);

static u32 restart_sge(struct qib_sge_state *ss, struct qib_swqe *wqe,
               u32 psn, u32 pmtu)
{
    u32 len;

    len = ((psn - wqe->psn) & QIB_PSN_MASK) * pmtu;
    ss->sge = wqe->sg_list[0];
    ss->sg_list = wqe->sg_list + 1;
    ss->num_sge = wqe->wr.num_sge;
    ss->total_len = wqe->length;
    qib_skip_sge(ss, len, 0);
    return wqe->length - len;
}

static void start_timer(struct qib_qp *qp)
{
    qp->s_flags |= QIB_S_TIMER;
    qp->s_timer.function = rc_timeout;
    /* 4.096 usec. * (1 << qp->timeout) */
    qp->s_timer.expires = jiffies + qp->timeout_jiffies;
    add_timer(&qp->s_timer);
}

static int qib_make_rc_ack(struct qib_ibdev *dev, struct qib_qp *qp,
               struct qib_other_headers *ohdr, u32 pmtu)
{
    struct qib_ack_entry *e;
    u32 hwords;
    u32 len;
    u32 bth0;
    u32 bth2;

    /* Don't send an ACK if we aren't supposed to. */
    if (!(ib_qib_state_ops[qp->state] & QIB_PROCESS_RECV_OK))
        goto bail;

    /* header size in 32-bit words LRH+BTH = (8+12)/4. */
    hwords = 5;

    switch (qp->s_ack_state) {
    case OP(RDMA_READ_RESPONSE_LAST):
    case OP(RDMA_READ_RESPONSE_ONLY):
        e = &qp->s_ack_queue[qp->s_tail_ack_queue];
        if (e->rdma_sge.mr) {
            qib_put_mr(e->rdma_sge.mr);
            e->rdma_sge.mr = NULL;
        }
        /* FALLTHROUGH */
    case OP(ATOMIC_ACKNOWLEDGE):
        /*
         * We can increment the tail pointer now that the last
         * response has been sent instead of only being
         * constructed.
         */
        if (++qp->s_tail_ack_queue > QIB_MAX_RDMA_ATOMIC)
            qp->s_tail_ack_queue = 0;
        /* FALLTHROUGH */
    case OP(SEND_ONLY):
    case OP(ACKNOWLEDGE):
        /* Check for no next entry in the queue. */
        if (qp->r_head_ack_queue == qp->s_tail_ack_queue) {
            if (qp->s_flags & QIB_S_ACK_PENDING)
                goto normal;
            goto bail;
        }

        e = &qp->s_ack_queue[qp->s_tail_ack_queue];
        if (e->opcode == OP(RDMA_READ_REQUEST)) {
            /*
             * If a RDMA read response is being resent and
             * we haven't seen the duplicate request yet,
             * then stop sending the remaining responses the
             * responder has seen until the requester resends it.
             */
            len = e->rdma_sge.sge_length;
            if (len && !e->rdma_sge.mr) {
                qp->s_tail_ack_queue = qp->r_head_ack_queue;
                goto bail;
            }
            /* Copy SGE state in case we need to resend */
            qp->s_rdma_mr = e->rdma_sge.mr;
            if (qp->s_rdma_mr)
                qib_get_mr(qp->s_rdma_mr);
            qp->s_ack_rdma_sge.sge = e->rdma_sge;
            qp->s_ack_rdma_sge.num_sge = 1;
            qp->s_cur_sge = &qp->s_ack_rdma_sge;
            if (len > pmtu) {
                len = pmtu;
                qp->s_ack_state = OP(RDMA_READ_RESPONSE_FIRST);
            } else {
                qp->s_ack_state = OP(RDMA_READ_RESPONSE_ONLY);
                e->sent = 1;
            }
            ohdr->u.aeth = qib_compute_aeth(qp);
            hwords++;
            qp->s_ack_rdma_psn = e->psn;
            bth2 = qp->s_ack_rdma_psn++ & QIB_PSN_MASK;
        } else {
            /* COMPARE_SWAP or FETCH_ADD */
            qp->s_cur_sge = NULL;
            len = 0;
            qp->s_ack_state = OP(ATOMIC_ACKNOWLEDGE);
            ohdr->u.at.aeth = qib_compute_aeth(qp);
            ohdr->u.at.atomic_ack_eth[0] =
                cpu_to_be32(e->atomic_data >> 32);
            ohdr->u.at.atomic_ack_eth[1] =
                cpu_to_be32(e->atomic_data);
            hwords += sizeof(ohdr->u.at) / sizeof(u32);
            bth2 = e->psn & QIB_PSN_MASK;
            e->sent = 1;
        }
        bth0 = qp->s_ack_state << 24;
        break;

    case OP(RDMA_READ_RESPONSE_FIRST):
        qp->s_ack_state = OP(RDMA_READ_RESPONSE_MIDDLE);
        /* FALLTHROUGH */
    case OP(RDMA_READ_RESPONSE_MIDDLE):
        qp->s_cur_sge = &qp->s_ack_rdma_sge;
        qp->s_rdma_mr = qp->s_ack_rdma_sge.sge.mr;
        if (qp->s_rdma_mr)
            qib_get_mr(qp->s_rdma_mr);
        len = qp->s_ack_rdma_sge.sge.sge_length;
        if (len > pmtu)
            len = pmtu;
        else {
            ohdr->u.aeth = qib_compute_aeth(qp);
            hwords++;
            qp->s_ack_state = OP(RDMA_READ_RESPONSE_LAST);
            e = &qp->s_ack_queue[qp->s_tail_ack_queue];
            e->sent = 1;
        }
        bth0 = qp->s_ack_state << 24;
        bth2 = qp->s_ack_rdma_psn++ & QIB_PSN_MASK;
        break;

    default:
normal:
        /*
         * Send a regular ACK.
         * Set the s_ack_state so we wait until after sending
         * the ACK before setting s_ack_state to ACKNOWLEDGE
         * (see above).
         */
        qp->s_ack_state = OP(SEND_ONLY);
        qp->s_flags &= ~QIB_S_ACK_PENDING;
        qp->s_cur_sge = NULL;
        if (qp->s_nak_state)
            ohdr->u.aeth =
                cpu_to_be32((qp->r_msn & QIB_MSN_MASK) |
                        (qp->s_nak_state <<
                         QIB_AETH_CREDIT_SHIFT));
        else
            ohdr->u.aeth = qib_compute_aeth(qp);
        hwords++;
        len = 0;
        bth0 = OP(ACKNOWLEDGE) << 24;
        bth2 = qp->s_ack_psn & QIB_PSN_MASK;
    }
    qp->s_rdma_ack_cnt++;
    qp->s_hdrwords = hwords;
    qp->s_cur_size = len;
    qib_make_ruc_header(qp, ohdr, bth0, bth2);
    return 1;

bail:
    qp->s_ack_state = OP(ACKNOWLEDGE);
    qp->s_flags &= ~(QIB_S_RESP_PENDING | QIB_S_ACK_PENDING);
    return 0;
}

int qib_make_rc_req(struct qib_qp *qp)
{
    struct qib_ibdev *dev = to_idev(qp->ibqp.device);
    struct qib_other_headers *ohdr;
    struct qib_sge_state *ss;
    struct qib_swqe *wqe;
    u32 hwords;
    u32 len;
    u32 bth0;
    u32 bth2;
    u32 pmtu = qp->pmtu;
    char newreq;
    unsigned long flags;
    int ret = 0;
    int delta;

    ohdr = &qp->s_hdr->u.oth;
    if (qp->remote_ah_attr.ah_flags & IB_AH_GRH)
        ohdr = &qp->s_hdr->u.l.oth;

    /*
     * The lock is needed to synchronize between the sending tasklet,
     * the receive interrupt handler, and timeout resends.
     */
    spin_lock_irqsave(&qp->s_lock, flags);

    /* Sending responses has higher priority over sending requests. */
    if ((qp->s_flags & QIB_S_RESP_PENDING) &&
        qib_make_rc_ack(dev, qp, ohdr, pmtu))
        goto done;

    if (!(ib_qib_state_ops[qp->state] & QIB_PROCESS_SEND_OK)) {
        if (!(ib_qib_state_ops[qp->state] & QIB_FLUSH_SEND))
            goto bail;
        /* We are in the error state, flush the work request. */
        if (qp->s_last == qp->s_head)
            goto bail;
        /* If DMAs are in progress, we can't flush immediately. */
        if (atomic_read(&qp->s_dma_busy)) {
            qp->s_flags |= QIB_S_WAIT_DMA;
            goto bail;
        }
        wqe = get_swqe_ptr(qp, qp->s_last);
        qib_send_complete(qp, wqe, qp->s_last != qp->s_acked ?
            IB_WC_SUCCESS : IB_WC_WR_FLUSH_ERR);
        /* will get called again */
        goto done;
    }

    if (qp->s_flags & (QIB_S_WAIT_RNR | QIB_S_WAIT_ACK))
        goto bail;

    if (qib_cmp24(qp->s_psn, qp->s_sending_hpsn) <= 0) {
        if (qib_cmp24(qp->s_sending_psn, qp->s_sending_hpsn) <= 0) {
            qp->s_flags |= QIB_S_WAIT_PSN;
            goto bail;
        }
        qp->s_sending_psn = qp->s_psn;
        qp->s_sending_hpsn = qp->s_psn - 1;
    }

    /* header size in 32-bit words LRH+BTH = (8+12)/4. */
    hwords = 5;
    bth0 = 0;

    /* Send a request. */
    wqe = get_swqe_ptr(qp, qp->s_cur);
    switch (qp->s_state) {
    default:
        if (!(ib_qib_state_ops[qp->state] & QIB_PROCESS_NEXT_SEND_OK))
            goto bail;
        /*
         * Resend an old request or start a new one.
         *
         * We keep track of the current SWQE so that
         * we don't reset the "furthest progress" state
         * if we need to back up.
         */
        newreq = 0;
        if (qp->s_cur == qp->s_tail) {
            /* Check if send work queue is empty. */
            if (qp->s_tail == qp->s_head)
                goto bail;
            /*
             * If a fence is requested, wait for previous
             * RDMA read and atomic operations to finish.
             */
            if ((wqe->wr.send_flags & IB_SEND_FENCE) &&
                qp->s_num_rd_atomic) {
                qp->s_flags |= QIB_S_WAIT_FENCE;
                goto bail;
            }
            wqe->psn = qp->s_next_psn;
            newreq = 1;
        }
        /*
         * Note that we have to be careful not to modify the
         * original work request since we may need to resend
         * it.
         */
        len = wqe->length;
        ss = &qp->s_sge;
        bth2 = qp->s_psn & QIB_PSN_MASK;
        switch (wqe->wr.opcode) {
        case IB_WR_SEND:
        case IB_WR_SEND_WITH_IMM:
            /* If no credit, return. */
            if (!(qp->s_flags & QIB_S_UNLIMITED_CREDIT) &&
                qib_cmp24(wqe->ssn, qp->s_lsn + 1) > 0) {
                qp->s_flags |= QIB_S_WAIT_SSN_CREDIT;
                goto bail;
            }
            wqe->lpsn = wqe->psn;
            if (len > pmtu) {
                wqe->lpsn += (len - 1) / pmtu;
                qp->s_state = OP(SEND_FIRST);
                len = pmtu;
                break;
            }
            if (wqe->wr.opcode == IB_WR_SEND)
                qp->s_state = OP(SEND_ONLY);
            else {
                qp->s_state = OP(SEND_ONLY_WITH_IMMEDIATE);
                /* Immediate data comes after the BTH */
                ohdr->u.imm_data = wqe->wr.ex.imm_data;
                hwords += 1;
            }
            if (wqe->wr.send_flags & IB_SEND_SOLICITED)
                bth0 |= IB_BTH_SOLICITED;
            bth2 |= IB_BTH_REQ_ACK;
            if (++qp->s_cur == qp->s_size)
                qp->s_cur = 0;
            break;

        case IB_WR_RDMA_WRITE:
            if (newreq && !(qp->s_flags & QIB_S_UNLIMITED_CREDIT))
                qp->s_lsn++;
            /* FALLTHROUGH */
        case IB_WR_RDMA_WRITE_WITH_IMM:
            /* If no credit, return. */
            if (!(qp->s_flags & QIB_S_UNLIMITED_CREDIT) &&
                qib_cmp24(wqe->ssn, qp->s_lsn + 1) > 0) {
                qp->s_flags |= QIB_S_WAIT_SSN_CREDIT;
                goto bail;
            }
            ohdr->u.rc.reth.vaddr =
                cpu_to_be64(wqe->wr.wr.rdma.remote_addr);
            ohdr->u.rc.reth.rkey =
                cpu_to_be32(wqe->wr.wr.rdma.rkey);
            ohdr->u.rc.reth.length = cpu_to_be32(len);
            hwords += sizeof(struct ib_reth) / sizeof(u32);
            wqe->lpsn = wqe->psn;
            if (len > pmtu) {
                wqe->lpsn += (len - 1) / pmtu;
                qp->s_state = OP(RDMA_WRITE_FIRST);
                len = pmtu;
                break;
            }
            if (wqe->wr.opcode == IB_WR_RDMA_WRITE)
                qp->s_state = OP(RDMA_WRITE_ONLY);
            else {
                qp->s_state =
                    OP(RDMA_WRITE_ONLY_WITH_IMMEDIATE);
                /* Immediate data comes after RETH */
                ohdr->u.rc.imm_data = wqe->wr.ex.imm_data;
                hwords += 1;
                if (wqe->wr.send_flags & IB_SEND_SOLICITED)
                    bth0 |= IB_BTH_SOLICITED;
            }
            bth2 |= IB_BTH_REQ_ACK;
            if (++qp->s_cur == qp->s_size)
                qp->s_cur = 0;
            break;

        case IB_WR_RDMA_READ:
            /*
             * Don't allow more operations to be started
             * than the QP limits allow.
             */
            if (newreq) {
                if (qp->s_num_rd_atomic >=
                    qp->s_max_rd_atomic) {
                    qp->s_flags |= QIB_S_WAIT_RDMAR;
                    goto bail;
                }
                qp->s_num_rd_atomic++;
                if (!(qp->s_flags & QIB_S_UNLIMITED_CREDIT))
                    qp->s_lsn++;
                /*
                 * Adjust s_next_psn to count the
                 * expected number of responses.
                 */
                if (len > pmtu)
                    qp->s_next_psn += (len - 1) / pmtu;
                wqe->lpsn = qp->s_next_psn++;
            }
            ohdr->u.rc.reth.vaddr =
                cpu_to_be64(wqe->wr.wr.rdma.remote_addr);
            ohdr->u.rc.reth.rkey =
                cpu_to_be32(wqe->wr.wr.rdma.rkey);
            ohdr->u.rc.reth.length = cpu_to_be32(len);
            qp->s_state = OP(RDMA_READ_REQUEST);
            hwords += sizeof(ohdr->u.rc.reth) / sizeof(u32);
            ss = NULL;
            len = 0;
            bth2 |= IB_BTH_REQ_ACK;
            if (++qp->s_cur == qp->s_size)
                qp->s_cur = 0;
            break;

        case IB_WR_ATOMIC_CMP_AND_SWP:
        case IB_WR_ATOMIC_FETCH_AND_ADD:
            /*
             * Don't allow more operations to be started
             * than the QP limits allow.
             */
            if (newreq) {
                if (qp->s_num_rd_atomic >=
                    qp->s_max_rd_atomic) {
                    qp->s_flags |= QIB_S_WAIT_RDMAR;
                    goto bail;
                }
                qp->s_num_rd_atomic++;
                if (!(qp->s_flags & QIB_S_UNLIMITED_CREDIT))
                    qp->s_lsn++;
                wqe->lpsn = wqe->psn;
            }
            if (wqe->wr.opcode == IB_WR_ATOMIC_CMP_AND_SWP) {
                qp->s_state = OP(COMPARE_SWAP);
                ohdr->u.atomic_eth.swap_data = cpu_to_be64(
                    wqe->wr.wr.atomic.swap);
                ohdr->u.atomic_eth.compare_data = cpu_to_be64(
                    wqe->wr.wr.atomic.compare_add);
            } else {
                qp->s_state = OP(FETCH_ADD);
                ohdr->u.atomic_eth.swap_data = cpu_to_be64(
                    wqe->wr.wr.atomic.compare_add);
                ohdr->u.atomic_eth.compare_data = 0;
            }
            ohdr->u.atomic_eth.vaddr[0] = cpu_to_be32(
                wqe->wr.wr.atomic.remote_addr >> 32);
            ohdr->u.atomic_eth.vaddr[1] = cpu_to_be32(
                wqe->wr.wr.atomic.remote_addr);
            ohdr->u.atomic_eth.rkey = cpu_to_be32(
                wqe->wr.wr.atomic.rkey);
            hwords += sizeof(struct ib_atomic_eth) / sizeof(u32);
            ss = NULL;
            len = 0;
            bth2 |= IB_BTH_REQ_ACK;
            if (++qp->s_cur == qp->s_size)
                qp->s_cur = 0;
            break;

        default:
            goto bail;
        }
        qp->s_sge.sge = wqe->sg_list[0];
        qp->s_sge.sg_list = wqe->sg_list + 1;
        qp->s_sge.num_sge = wqe->wr.num_sge;
        qp->s_sge.total_len = wqe->length;
        qp->s_len = wqe->length;
        if (newreq) {
            qp->s_tail++;
            if (qp->s_tail >= qp->s_size)
                qp->s_tail = 0;
        }
        if (wqe->wr.opcode == IB_WR_RDMA_READ)
            qp->s_psn = wqe->lpsn + 1;
        else {
            qp->s_psn++;
            if (qib_cmp24(qp->s_psn, qp->s_next_psn) > 0)
                qp->s_next_psn = qp->s_psn;
        }
        break;

    case OP(RDMA_READ_RESPONSE_FIRST):
        /*
         * qp->s_state is normally set to the opcode of the
         * last packet constructed for new requests and therefore
         * is never set to RDMA read response.
         * RDMA_READ_RESPONSE_FIRST is used by the ACK processing
         * thread to indicate a SEND needs to be restarted from an
         * earlier PSN without interferring with the sending thread.
         * See qib_restart_rc().
         */
        qp->s_len = restart_sge(&qp->s_sge, wqe, qp->s_psn, pmtu);
        /* FALLTHROUGH */
    case OP(SEND_FIRST):
        qp->s_state = OP(SEND_MIDDLE);
        /* FALLTHROUGH */
    case OP(SEND_MIDDLE):
        bth2 = qp->s_psn++ & QIB_PSN_MASK;
        if (qib_cmp24(qp->s_psn, qp->s_next_psn) > 0)
            qp->s_next_psn = qp->s_psn;
        ss = &qp->s_sge;
        len = qp->s_len;
        if (len > pmtu) {
            len = pmtu;
            break;
        }
        if (wqe->wr.opcode == IB_WR_SEND)
            qp->s_state = OP(SEND_LAST);
        else {
            qp->s_state = OP(SEND_LAST_WITH_IMMEDIATE);
            /* Immediate data comes after the BTH */
            ohdr->u.imm_data = wqe->wr.ex.imm_data;
            hwords += 1;
        }
        if (wqe->wr.send_flags & IB_SEND_SOLICITED)
            bth0 |= IB_BTH_SOLICITED;
        bth2 |= IB_BTH_REQ_ACK;
        qp->s_cur++;
        if (qp->s_cur >= qp->s_size)
            qp->s_cur = 0;
        break;

    case OP(RDMA_READ_RESPONSE_LAST):
        /*
         * qp->s_state is normally set to the opcode of the
         * last packet constructed for new requests and therefore
         * is never set to RDMA read response.
         * RDMA_READ_RESPONSE_LAST is used by the ACK processing
         * thread to indicate a RDMA write needs to be restarted from
         * an earlier PSN without interferring with the sending thread.
         * See qib_restart_rc().
         */
        qp->s_len = restart_sge(&qp->s_sge, wqe, qp->s_psn, pmtu);
        /* FALLTHROUGH */
    case OP(RDMA_WRITE_FIRST):
        qp->s_state = OP(RDMA_WRITE_MIDDLE);
        /* FALLTHROUGH */
    case OP(RDMA_WRITE_MIDDLE):
        bth2 = qp->s_psn++ & QIB_PSN_MASK;
        if (qib_cmp24(qp->s_psn, qp->s_next_psn) > 0)
            qp->s_next_psn = qp->s_psn;
        ss = &qp->s_sge;
        len = qp->s_len;
        if (len > pmtu) {
            len = pmtu;
            break;
        }
        if (wqe->wr.opcode == IB_WR_RDMA_WRITE)
            qp->s_state = OP(RDMA_WRITE_LAST);
        else {
            qp->s_state = OP(RDMA_WRITE_LAST_WITH_IMMEDIATE);
            /* Immediate data comes after the BTH */
            ohdr->u.imm_data = wqe->wr.ex.imm_data;
            hwords += 1;
            if (wqe->wr.send_flags & IB_SEND_SOLICITED)
                bth0 |= IB_BTH_SOLICITED;
        }
        bth2 |= IB_BTH_REQ_ACK;
        qp->s_cur++;
        if (qp->s_cur >= qp->s_size)
            qp->s_cur = 0;
        break;

    case OP(RDMA_READ_RESPONSE_MIDDLE):
        /*
         * qp->s_state is normally set to the opcode of the
         * last packet constructed for new requests and therefore
         * is never set to RDMA read response.
         * RDMA_READ_RESPONSE_MIDDLE is used by the ACK processing
         * thread to indicate a RDMA read needs to be restarted from
         * an earlier PSN without interferring with the sending thread.
         * See qib_restart_rc().
         */
        len = ((qp->s_psn - wqe->psn) & QIB_PSN_MASK) * pmtu;
        ohdr->u.rc.reth.vaddr =
            cpu_to_be64(wqe->wr.wr.rdma.remote_addr + len);
        ohdr->u.rc.reth.rkey =
            cpu_to_be32(wqe->wr.wr.rdma.rkey);
        ohdr->u.rc.reth.length = cpu_to_be32(wqe->length - len);
        qp->s_state = OP(RDMA_READ_REQUEST);
        hwords += sizeof(ohdr->u.rc.reth) / sizeof(u32);
        bth2 = (qp->s_psn & QIB_PSN_MASK) | IB_BTH_REQ_ACK;
        qp->s_psn = wqe->lpsn + 1;
        ss = NULL;
        len = 0;
        qp->s_cur++;
        if (qp->s_cur == qp->s_size)
            qp->s_cur = 0;
        break;
    }
    qp->s_sending_hpsn = bth2;
    delta = (((int) bth2 - (int) wqe->psn) << 8) >> 8;
    if (delta && delta % QIB_PSN_CREDIT == 0)
        bth2 |= IB_BTH_REQ_ACK;
    if (qp->s_flags & QIB_S_SEND_ONE) {
        qp->s_flags &= ~QIB_S_SEND_ONE;
        qp->s_flags |= QIB_S_WAIT_ACK;
        bth2 |= IB_BTH_REQ_ACK;
    }
    qp->s_len -= len;
    qp->s_hdrwords = hwords;
    qp->s_cur_sge = ss;
    qp->s_cur_size = len;
    qib_make_ruc_header(qp, ohdr, bth0 | (qp->s_state << 24), bth2);
done:
    ret = 1;
    goto unlock;

bail:
    qp->s_flags &= ~QIB_S_BUSY;
unlock:
    spin_unlock_irqrestore(&qp->s_lock, flags);
    return ret;
}

void qib_send_rc_ack(struct qib_qp *qp)
{
    struct qib_devdata *dd = dd_from_ibdev(qp->ibqp.device);
    struct qib_ibport *ibp = to_iport(qp->ibqp.device, qp->port_num);
    struct qib_pportdata *ppd = ppd_from_ibp(ibp);
    u64 pbc;
    u16 lrh0;
    u32 bth0;
    u32 hwords;
    u32 pbufn;
    u32 __iomem *piobuf;
    struct qib_ib_header hdr;
    struct qib_other_headers *ohdr;
    u32 control;
    unsigned long flags;

    spin_lock_irqsave(&qp->s_lock, flags);

    if (!(ib_qib_state_ops[qp->state] & QIB_PROCESS_RECV_OK))
        goto unlock;

    /* Don't send ACK or NAK if a RDMA read or atomic is pending. */
    if ((qp->s_flags & QIB_S_RESP_PENDING) || qp->s_rdma_ack_cnt)
        goto queue_ack;

    /* Construct the header with s_lock held so APM doesn't change it. */
    ohdr = &hdr.u.oth;
    lrh0 = QIB_LRH_BTH;
    /* header size in 32-bit words LRH+BTH+AETH = (8+12+4)/4. */
    hwords = 6;
    if (unlikely(qp->remote_ah_attr.ah_flags & IB_AH_GRH)) {
        hwords += qib_make_grh(ibp, &hdr.u.l.grh,
                       &qp->remote_ah_attr.grh, hwords, 0);
        ohdr = &hdr.u.l.oth;
        lrh0 = QIB_LRH_GRH;
    }
    /* read pkey_index w/o lock (its atomic) */
    bth0 = qib_get_pkey(ibp, qp->s_pkey_index) | (OP(ACKNOWLEDGE) << 24);
    if (qp->s_mig_state == IB_MIG_MIGRATED)
        bth0 |= IB_BTH_MIG_REQ;
    if (qp->r_nak_state)
        ohdr->u.aeth = cpu_to_be32((qp->r_msn & QIB_MSN_MASK) |
                        (qp->r_nak_state <<
                         QIB_AETH_CREDIT_SHIFT));
    else
        ohdr->u.aeth = qib_compute_aeth(qp);
    lrh0 |= ibp->sl_to_vl[qp->remote_ah_attr.sl] << 12 |
        qp->remote_ah_attr.sl << 4;
    hdr.lrh[0] = cpu_to_be16(lrh0);
    hdr.lrh[1] = cpu_to_be16(qp->remote_ah_attr.dlid);
    hdr.lrh[2] = cpu_to_be16(hwords + SIZE_OF_CRC);
    hdr.lrh[3] = cpu_to_be16(ppd->lid | qp->remote_ah_attr.src_path_bits);
    ohdr->bth[0] = cpu_to_be32(bth0);
    ohdr->bth[1] = cpu_to_be32(qp->remote_qpn);
    ohdr->bth[2] = cpu_to_be32(qp->r_ack_psn & QIB_PSN_MASK);

    spin_unlock_irqrestore(&qp->s_lock, flags);

    /* Don't try to send ACKs if the link isn't ACTIVE */
    if (!(ppd->lflags & QIBL_LINKACTIVE))
        goto done;

    control = dd->f_setpbc_control(ppd, hwords + SIZE_OF_CRC,
                       qp->s_srate, lrh0 >> 12);
    /* length is + 1 for the control dword */
    pbc = ((u64) control << 32) | (hwords + 1);

    piobuf = dd->f_getsendbuf(ppd, pbc, &pbufn);
    if (!piobuf) {
        /*
         * We are out of PIO buffers at the moment.
         * Pass responsibility for sending the ACK to the
         * send tasklet so that when a PIO buffer becomes
         * available, the ACK is sent ahead of other outgoing
         * packets.
         */
        spin_lock_irqsave(&qp->s_lock, flags);
        goto queue_ack;
    }

    /*
     * Write the pbc.
     * We have to flush after the PBC for correctness
     * on some cpus or WC buffer can be written out of order.
     */
    writeq(pbc, piobuf);

    if (dd->flags & QIB_PIO_FLUSH_WC) {
        u32 *hdrp = (u32 *) &hdr;

        qib_flush_wc();
        qib_pio_copy(piobuf + 2, hdrp, hwords - 1);
        qib_flush_wc();
        __raw_writel(hdrp[hwords - 1], piobuf + hwords + 1);
    } else
        qib_pio_copy(piobuf + 2, (u32 *) &hdr, hwords);

    if (dd->flags & QIB_USE_SPCL_TRIG) {
        u32 spcl_off = (pbufn >= dd->piobcnt2k) ? 2047 : 1023;

        qib_flush_wc();
        __raw_writel(0xaebecede, piobuf + spcl_off);
    }

    qib_flush_wc();
    qib_sendbuf_done(dd, pbufn);

    ibp->n_unicast_xmit++;
    goto done;

queue_ack:
    if (ib_qib_state_ops[qp->state] & QIB_PROCESS_RECV_OK) {
        ibp->n_rc_qacks++;
        qp->s_flags |= QIB_S_ACK_PENDING | QIB_S_RESP_PENDING;
        qp->s_nak_state = qp->r_nak_state;
        qp->s_ack_psn = qp->r_ack_psn;

        /* Schedule the send tasklet. */
        qib_schedule_send(qp);
    }
unlock:
    spin_unlock_irqrestore(&qp->s_lock, flags);
done:
    return;
}

static void reset_psn(struct qib_qp *qp, u32 psn)
{
    u32 n = qp->s_acked;
    struct qib_swqe *wqe = get_swqe_ptr(qp, n);
    u32 opcode;

    qp->s_cur = n;

    /*
     * If we are starting the request from the beginning,
     * let the normal send code handle initialization.
     */
    if (qib_cmp24(psn, wqe->psn) <= 0) {
        qp->s_state = OP(SEND_LAST);
        goto done;
    }

    /* Find the work request opcode corresponding to the given PSN. */
    opcode = wqe->wr.opcode;
    for (;;) {
        int diff;

        if (++n == qp->s_size)
            n = 0;
        if (n == qp->s_tail)
            break;
        wqe = get_swqe_ptr(qp, n);
        diff = qib_cmp24(psn, wqe->psn);
        if (diff < 0)
            break;
        qp->s_cur = n;
        /*
         * If we are starting the request from the beginning,
         * let the normal send code handle initialization.
         */
        if (diff == 0) {
            qp->s_state = OP(SEND_LAST);
            goto done;
        }
        opcode = wqe->wr.opcode;
    }

    /*
     * Set the state to restart in the middle of a request.
     * Don't change the s_sge, s_cur_sge, or s_cur_size.
     * See qib_make_rc_req().
     */
    switch (opcode) {
    case IB_WR_SEND:
    case IB_WR_SEND_WITH_IMM:
        qp->s_state = OP(RDMA_READ_RESPONSE_FIRST);
        break;

    case IB_WR_RDMA_WRITE:
    case IB_WR_RDMA_WRITE_WITH_IMM:
        qp->s_state = OP(RDMA_READ_RESPONSE_LAST);
        break;

    case IB_WR_RDMA_READ:
        qp->s_state = OP(RDMA_READ_RESPONSE_MIDDLE);
        break;

    default:
        /*
         * This case shouldn't happen since its only
         * one PSN per req.
         */
        qp->s_state = OP(SEND_LAST);
    }
done:
    qp->s_psn = psn;
    /*
     * Set QIB_S_WAIT_PSN as qib_rc_complete() may start the timer
     * asynchronously before the send tasklet can get scheduled.
     * Doing it in qib_make_rc_req() is too late.
     */
    if ((qib_cmp24(qp->s_psn, qp->s_sending_hpsn) <= 0) &&
        (qib_cmp24(qp->s_sending_psn, qp->s_sending_hpsn) <= 0))
        qp->s_flags |= QIB_S_WAIT_PSN;
}

/*
 * Back up requester to resend the last un-ACKed request.
 * The QP r_lock and s_lock should be held and interrupts disabled.
 */
static void qib_restart_rc(struct qib_qp *qp, u32 psn, int wait)
{
    struct qib_swqe *wqe = get_swqe_ptr(qp, qp->s_acked);
    struct qib_ibport *ibp;

    if (qp->s_retry == 0) {
        if (qp->s_mig_state == IB_MIG_ARMED) {
            qib_migrate_qp(qp);
            qp->s_retry = qp->s_retry_cnt;
        } else if (qp->s_last == qp->s_acked) {
            qib_send_complete(qp, wqe, IB_WC_RETRY_EXC_ERR);
            qib_error_qp(qp, IB_WC_WR_FLUSH_ERR);
            return;
        } else /* XXX need to handle delayed completion */
            return;
    } else
        qp->s_retry--;

    ibp = to_iport(qp->ibqp.device, qp->port_num);
    if (wqe->wr.opcode == IB_WR_RDMA_READ)
        ibp->n_rc_resends++;
    else
        ibp->n_rc_resends += (qp->s_psn - psn) & QIB_PSN_MASK;

    qp->s_flags &= ~(QIB_S_WAIT_FENCE | QIB_S_WAIT_RDMAR |
             QIB_S_WAIT_SSN_CREDIT | QIB_S_WAIT_PSN |
             QIB_S_WAIT_ACK);
    if (wait)
        qp->s_flags |= QIB_S_SEND_ONE;
    reset_psn(qp, psn);
}

/*
 * This is called from s_timer for missing responses.
 */
static void rc_timeout(unsigned long arg)
{
    struct qib_qp *qp = (struct qib_qp *)arg;
    struct qib_ibport *ibp;
    unsigned long flags;

    spin_lock_irqsave(&qp->r_lock, flags);
    spin_lock(&qp->s_lock);
    if (qp->s_flags & QIB_S_TIMER) {
        ibp = to_iport(qp->ibqp.device, qp->port_num);
        ibp->n_rc_timeouts++;
        qp->s_flags &= ~QIB_S_TIMER;
        del_timer(&qp->s_timer);
        qib_restart_rc(qp, qp->s_last_psn + 1, 1);
        qib_schedule_send(qp);
    }
    spin_unlock(&qp->s_lock);
    spin_unlock_irqrestore(&qp->r_lock, flags);
}

/*
 * This is called from s_timer for RNR timeouts.
 */
void qib_rc_rnr_retry(unsigned long arg)
{
    struct qib_qp *qp = (struct qib_qp *)arg;
    unsigned long flags;

    spin_lock_irqsave(&qp->s_lock, flags);
    if (qp->s_flags & QIB_S_WAIT_RNR) {
        qp->s_flags &= ~QIB_S_WAIT_RNR;
        del_timer(&qp->s_timer);
        qib_schedule_send(qp);
    }
    spin_unlock_irqrestore(&qp->s_lock, flags);
}

/*
 * Set qp->s_sending_psn to the next PSN after the given one.
 * This would be psn+1 except when RDMA reads are present.
 */
static void reset_sending_psn(struct qib_qp *qp, u32 psn)
{
    struct qib_swqe *wqe;
    u32 n = qp->s_last;

    /* Find the work request corresponding to the given PSN. */
    for (;;) {
        wqe = get_swqe_ptr(qp, n);
        if (qib_cmp24(psn, wqe->lpsn) <= 0) {
            if (wqe->wr.opcode == IB_WR_RDMA_READ)
                qp->s_sending_psn = wqe->lpsn + 1;
            else
                qp->s_sending_psn = psn + 1;
            break;
        }
        if (++n == qp->s_size)
            n = 0;
        if (n == qp->s_tail)
            break;
    }
}

/*
 * This should be called with the QP s_lock held and interrupts disabled.
 */
void qib_rc_send_complete(struct qib_qp *qp, struct qib_ib_header *hdr)
{
    struct qib_other_headers *ohdr;
    struct qib_swqe *wqe;
    struct ib_wc wc;
    unsigned i;
    u32 opcode;
    u32 psn;

    if (!(ib_qib_state_ops[qp->state] & QIB_PROCESS_OR_FLUSH_SEND))
        return;

    /* Find out where the BTH is */
    if ((be16_to_cpu(hdr->lrh[0]) & 3) == QIB_LRH_BTH)
        ohdr = &hdr->u.oth;
    else
        ohdr = &hdr->u.l.oth;

    opcode = be32_to_cpu(ohdr->bth[0]) >> 24;
    if (opcode >= OP(RDMA_READ_RESPONSE_FIRST) &&
        opcode <= OP(ATOMIC_ACKNOWLEDGE)) {
        WARN_ON(!qp->s_rdma_ack_cnt);
        qp->s_rdma_ack_cnt--;
        return;
    }

    psn = be32_to_cpu(ohdr->bth[2]);
    reset_sending_psn(qp, psn);

    /*
     * Start timer after a packet requesting an ACK has been sent and
     * there are still requests that haven't been acked.
     */
    if ((psn & IB_BTH_REQ_ACK) && qp->s_acked != qp->s_tail &&
        !(qp->s_flags & (QIB_S_TIMER | QIB_S_WAIT_RNR | QIB_S_WAIT_PSN)) &&
        (ib_qib_state_ops[qp->state] & QIB_PROCESS_RECV_OK))
        start_timer(qp);

    while (qp->s_last != qp->s_acked) {
        wqe = get_swqe_ptr(qp, qp->s_last);
        if (qib_cmp24(wqe->lpsn, qp->s_sending_psn) >= 0 &&
            qib_cmp24(qp->s_sending_psn, qp->s_sending_hpsn) <= 0)
            break;
        for (i = 0; i < wqe->wr.num_sge; i++) {
            struct qib_sge *sge = &wqe->sg_list[i];

            qib_put_mr(sge->mr);
        }
        /* Post a send completion queue entry if requested. */
        if (!(qp->s_flags & QIB_S_SIGNAL_REQ_WR) ||
            (wqe->wr.send_flags & IB_SEND_SIGNALED)) {
            memset(&wc, 0, sizeof wc);
            wc.wr_id = wqe->wr.wr_id;
            wc.status = IB_WC_SUCCESS;
            wc.opcode = ib_qib_wc_opcode[wqe->wr.opcode];
            wc.byte_len = wqe->length;
            wc.qp = &qp->ibqp;
            qib_cq_enter(to_icq(qp->ibqp.send_cq), &wc, 0);
        }
        if (++qp->s_last >= qp->s_size)
            qp->s_last = 0;
    }
    /*
     * If we were waiting for sends to complete before resending,
     * and they are now complete, restart sending.
     */
    if (qp->s_flags & QIB_S_WAIT_PSN &&
        qib_cmp24(qp->s_sending_psn, qp->s_sending_hpsn) > 0) {
        qp->s_flags &= ~QIB_S_WAIT_PSN;
        qp->s_sending_psn = qp->s_psn;
        qp->s_sending_hpsn = qp->s_psn - 1;
        qib_schedule_send(qp);
    }
}

static inline void update_last_psn(struct qib_qp *qp, u32 psn)
{
    qp->s_last_psn = psn;
}

/*
 * Generate a SWQE completion.
 * This is similar to qib_send_complete but has to check to be sure
 * that the SGEs are not being referenced if the SWQE is being resent.
 */
static struct qib_swqe *do_rc_completion(struct qib_qp *qp,
                     struct qib_swqe *wqe,
                     struct qib_ibport *ibp)
{
    struct ib_wc wc;
    unsigned i;

    /*
     * Don't decrement refcount and don't generate a
     * completion if the SWQE is being resent until the send
     * is finished.
     */
    if (qib_cmp24(wqe->lpsn, qp->s_sending_psn) < 0 ||
        qib_cmp24(qp->s_sending_psn, qp->s_sending_hpsn) > 0) {
        for (i = 0; i < wqe->wr.num_sge; i++) {
            struct qib_sge *sge = &wqe->sg_list[i];

            qib_put_mr(sge->mr);
        }
        /* Post a send completion queue entry if requested. */
        if (!(qp->s_flags & QIB_S_SIGNAL_REQ_WR) ||
            (wqe->wr.send_flags & IB_SEND_SIGNALED)) {
            memset(&wc, 0, sizeof wc);
            wc.wr_id = wqe->wr.wr_id;
            wc.status = IB_WC_SUCCESS;
            wc.opcode = ib_qib_wc_opcode[wqe->wr.opcode];
            wc.byte_len = wqe->length;
            wc.qp = &qp->ibqp;
            qib_cq_enter(to_icq(qp->ibqp.send_cq), &wc, 0);
        }
        if (++qp->s_last >= qp->s_size)
            qp->s_last = 0;
    } else
        ibp->n_rc_delayed_comp++;

    qp->s_retry = qp->s_retry_cnt;
    update_last_psn(qp, wqe->lpsn);

    /*
     * If we are completing a request which is in the process of
     * being resent, we can stop resending it since we know the
     * responder has already seen it.
     */
    if (qp->s_acked == qp->s_cur) {
        if (++qp->s_cur >= qp->s_size)
            qp->s_cur = 0;
        qp->s_acked = qp->s_cur;
        wqe = get_swqe_ptr(qp, qp->s_cur);
        if (qp->s_acked != qp->s_tail) {
            qp->s_state = OP(SEND_LAST);
            qp->s_psn = wqe->psn;
        }
    } else {
        if (++qp->s_acked >= qp->s_size)
            qp->s_acked = 0;
        if (qp->state == IB_QPS_SQD && qp->s_acked == qp->s_cur)
            qp->s_draining = 0;
        wqe = get_swqe_ptr(qp, qp->s_acked);
    }
    return wqe;
}

static int do_rc_ack(struct qib_qp *qp, u32 aeth, u32 psn, int opcode,
             u64 val, struct qib_ctxtdata *rcd)
{
    struct qib_ibport *ibp;
    enum ib_wc_status status;
    struct qib_swqe *wqe;
    int ret = 0;
    u32 ack_psn;
    int diff;

    /* Remove QP from retry timer */
    if (qp->s_flags & (QIB_S_TIMER | QIB_S_WAIT_RNR)) {
        qp->s_flags &= ~(QIB_S_TIMER | QIB_S_WAIT_RNR);
        del_timer(&qp->s_timer);
    }

    /*
     * Note that NAKs implicitly ACK outstanding SEND and RDMA write
     * requests and implicitly NAK RDMA read and atomic requests issued
     * before the NAK'ed request.  The MSN won't include the NAK'ed
     * request but will include an ACK'ed request(s).
     */
    ack_psn = psn;
    if (aeth >> 29)
        ack_psn--;
    wqe = get_swqe_ptr(qp, qp->s_acked);
    ibp = to_iport(qp->ibqp.device, qp->port_num);

    /*
     * The MSN might be for a later WQE than the PSN indicates so
     * only complete WQEs that the PSN finishes.
     */
    while ((diff = qib_cmp24(ack_psn, wqe->lpsn)) >= 0) {
        /*
         * RDMA_READ_RESPONSE_ONLY is a special case since
         * we want to generate completion events for everything
         * before the RDMA read, copy the data, then generate
         * the completion for the read.
         */
        if (wqe->wr.opcode == IB_WR_RDMA_READ &&
            opcode == OP(RDMA_READ_RESPONSE_ONLY) &&
            diff == 0) {
            ret = 1;
            goto bail;
        }
        /*
         * If this request is a RDMA read or atomic, and the ACK is
         * for a later operation, this ACK NAKs the RDMA read or
         * atomic.  In other words, only a RDMA_READ_LAST or ONLY
         * can ACK a RDMA read and likewise for atomic ops.  Note
         * that the NAK case can only happen if relaxed ordering is
         * used and requests are sent after an RDMA read or atomic
         * is sent but before the response is received.
         */
        if ((wqe->wr.opcode == IB_WR_RDMA_READ &&
             (opcode != OP(RDMA_READ_RESPONSE_LAST) || diff != 0)) ||
            ((wqe->wr.opcode == IB_WR_ATOMIC_CMP_AND_SWP ||
              wqe->wr.opcode == IB_WR_ATOMIC_FETCH_AND_ADD) &&
             (opcode != OP(ATOMIC_ACKNOWLEDGE) || diff != 0))) {
            /* Retry this request. */
            if (!(qp->r_flags & QIB_R_RDMAR_SEQ)) {
                qp->r_flags |= QIB_R_RDMAR_SEQ;
                qib_restart_rc(qp, qp->s_last_psn + 1, 0);
                if (list_empty(&qp->rspwait)) {
                    qp->r_flags |= QIB_R_RSP_SEND;
                    atomic_inc(&qp->refcount);
                    list_add_tail(&qp->rspwait,
                              &rcd->qp_wait_list);
                }
            }
            /*
             * No need to process the ACK/NAK since we are
             * restarting an earlier request.
             */
            goto bail;
        }
        if (wqe->wr.opcode == IB_WR_ATOMIC_CMP_AND_SWP ||
            wqe->wr.opcode == IB_WR_ATOMIC_FETCH_AND_ADD) {
            u64 *vaddr = wqe->sg_list[0].vaddr;
            *vaddr = val;
        }
        if (qp->s_num_rd_atomic &&
            (wqe->wr.opcode == IB_WR_RDMA_READ ||
             wqe->wr.opcode == IB_WR_ATOMIC_CMP_AND_SWP ||
             wqe->wr.opcode == IB_WR_ATOMIC_FETCH_AND_ADD)) {
            qp->s_num_rd_atomic--;
            /* Restart sending task if fence is complete */
            if ((qp->s_flags & QIB_S_WAIT_FENCE) &&
                !qp->s_num_rd_atomic) {
                qp->s_flags &= ~(QIB_S_WAIT_FENCE |
                         QIB_S_WAIT_ACK);
                qib_schedule_send(qp);
            } else if (qp->s_flags & QIB_S_WAIT_RDMAR) {
                qp->s_flags &= ~(QIB_S_WAIT_RDMAR |
                         QIB_S_WAIT_ACK);
                qib_schedule_send(qp);
            }
        }
        wqe = do_rc_completion(qp, wqe, ibp);
        if (qp->s_acked == qp->s_tail)
            break;
    }

    switch (aeth >> 29) {
    case 0:         /* ACK */
        ibp->n_rc_acks++;
        if (qp->s_acked != qp->s_tail) {
            /*
             * We are expecting more ACKs so
             * reset the retransmit timer.
             */
            start_timer(qp);
            /*
             * We can stop resending the earlier packets and
             * continue with the next packet the receiver wants.
             */
            if (qib_cmp24(qp->s_psn, psn) <= 0)
                reset_psn(qp, psn + 1);
        } else if (qib_cmp24(qp->s_psn, psn) <= 0) {
            qp->s_state = OP(SEND_LAST);
            qp->s_psn = psn + 1;
        }
        if (qp->s_flags & QIB_S_WAIT_ACK) {
            qp->s_flags &= ~QIB_S_WAIT_ACK;
            qib_schedule_send(qp);
        }
        qib_get_credit(qp, aeth);
        qp->s_rnr_retry = qp->s_rnr_retry_cnt;
        qp->s_retry = qp->s_retry_cnt;
        update_last_psn(qp, psn);
        ret = 1;
        goto bail;

    case 1:         /* RNR NAK */
        ibp->n_rnr_naks++;
        if (qp->s_acked == qp->s_tail)
            goto bail;
        if (qp->s_flags & QIB_S_WAIT_RNR)
            goto bail;
        if (qp->s_rnr_retry == 0) {
            status = IB_WC_RNR_RETRY_EXC_ERR;
            goto class_b;
        }
        if (qp->s_rnr_retry_cnt < 7)
            qp->s_rnr_retry--;

        /* The last valid PSN is the previous PSN. */
        update_last_psn(qp, psn - 1);

        ibp->n_rc_resends += (qp->s_psn - psn) & QIB_PSN_MASK;

        reset_psn(qp, psn);

        qp->s_flags &= ~(QIB_S_WAIT_SSN_CREDIT | QIB_S_WAIT_ACK);
        qp->s_flags |= QIB_S_WAIT_RNR;
        qp->s_timer.function = qib_rc_rnr_retry;
        qp->s_timer.expires = jiffies + usecs_to_jiffies(
            ib_qib_rnr_table[(aeth >> QIB_AETH_CREDIT_SHIFT) &
                       QIB_AETH_CREDIT_MASK]);
        add_timer(&qp->s_timer);
        goto bail;

    case 3:         /* NAK */
        if (qp->s_acked == qp->s_tail)
            goto bail;
        /* The last valid PSN is the previous PSN. */
        update_last_psn(qp, psn - 1);
        switch ((aeth >> QIB_AETH_CREDIT_SHIFT) &
            QIB_AETH_CREDIT_MASK) {
        case 0: /* PSN sequence error */
            ibp->n_seq_naks++;
            /*
             * Back up to the responder's expected PSN.
             * Note that we might get a NAK in the middle of an
             * RDMA READ response which terminates the RDMA
             * READ.
             */
            qib_restart_rc(qp, psn, 0);
            qib_schedule_send(qp);
            break;

        case 1: /* Invalid Request */
            status = IB_WC_REM_INV_REQ_ERR;
            ibp->n_other_naks++;
            goto class_b;

        case 2: /* Remote Access Error */
            status = IB_WC_REM_ACCESS_ERR;
            ibp->n_other_naks++;
            goto class_b;

        case 3: /* Remote Operation Error */
            status = IB_WC_REM_OP_ERR;
            ibp->n_other_naks++;
class_b:
            if (qp->s_last == qp->s_acked) {
                qib_send_complete(qp, wqe, status);
                qib_error_qp(qp, IB_WC_WR_FLUSH_ERR);
            }
            break;

        default:
            /* Ignore other reserved NAK error codes */
            goto reserved;
        }
        qp->s_retry = qp->s_retry_cnt;
        qp->s_rnr_retry = qp->s_rnr_retry_cnt;
        goto bail;

    default:                /* 2: reserved */
reserved:
        /* Ignore reserved NAK codes. */
        goto bail;
    }

bail:
    return ret;
}

/*
 * We have seen an out of sequence RDMA read middle or last packet.
 * This ACKs SENDs and RDMA writes up to the first RDMA read or atomic SWQE.
 */
static void rdma_seq_err(struct qib_qp *qp, struct qib_ibport *ibp, u32 psn,
             struct qib_ctxtdata *rcd)
{
    struct qib_swqe *wqe;

    /* Remove QP from retry timer */
    if (qp->s_flags & (QIB_S_TIMER | QIB_S_WAIT_RNR)) {
        qp->s_flags &= ~(QIB_S_TIMER | QIB_S_WAIT_RNR);
        del_timer(&qp->s_timer);
    }

    wqe = get_swqe_ptr(qp, qp->s_acked);

    while (qib_cmp24(psn, wqe->lpsn) > 0) {
        if (wqe->wr.opcode == IB_WR_RDMA_READ ||
            wqe->wr.opcode == IB_WR_ATOMIC_CMP_AND_SWP ||
            wqe->wr.opcode == IB_WR_ATOMIC_FETCH_AND_ADD)
            break;
        wqe = do_rc_completion(qp, wqe, ibp);
    }

    ibp->n_rdma_seq++;
    qp->r_flags |= QIB_R_RDMAR_SEQ;
    qib_restart_rc(qp, qp->s_last_psn + 1, 0);
    if (list_empty(&qp->rspwait)) {
        qp->r_flags |= QIB_R_RSP_SEND;
        atomic_inc(&qp->refcount);
        list_add_tail(&qp->rspwait, &rcd->qp_wait_list);
    }
}

static void qib_rc_rcv_resp(struct qib_ibport *ibp,
                struct qib_other_headers *ohdr,
                void *data, u32 tlen,
                struct qib_qp *qp,
                u32 opcode,
                u32 psn, u32 hdrsize, u32 pmtu,
                struct qib_ctxtdata *rcd)
{
    struct qib_swqe *wqe;
    struct qib_pportdata *ppd = ppd_from_ibp(ibp);
    enum ib_wc_status status;
    unsigned long flags;
    int diff;
    u32 pad;
    u32 aeth;
    u64 val;

    if (opcode != OP(RDMA_READ_RESPONSE_MIDDLE)) {
        /*
         * If ACK'd PSN on SDMA busy list try to make progress to
         * reclaim SDMA credits.
         */
        if ((qib_cmp24(psn, qp->s_sending_psn) >= 0) &&
            (qib_cmp24(qp->s_sending_psn, qp->s_sending_hpsn) <= 0)) {

            /*
             * If send tasklet not running attempt to progress
             * SDMA queue.
             */
            if (!(qp->s_flags & QIB_S_BUSY)) {
                /* Acquire SDMA Lock */
                spin_lock_irqsave(&ppd->sdma_lock, flags);
                /* Invoke sdma make progress */
                qib_sdma_make_progress(ppd);
                /* Release SDMA Lock */
                spin_unlock_irqrestore(&ppd->sdma_lock, flags);
            }
        }
    }

    spin_lock_irqsave(&qp->s_lock, flags);
    if (!(ib_qib_state_ops[qp->state] & QIB_PROCESS_RECV_OK))
        goto ack_done;

    /* Ignore invalid responses. */
    if (qib_cmp24(psn, qp->s_next_psn) >= 0)
        goto ack_done;

    /* Ignore duplicate responses. */
    diff = qib_cmp24(psn, qp->s_last_psn);
    if (unlikely(diff <= 0)) {
        /* Update credits for "ghost" ACKs */
        if (diff == 0 && opcode == OP(ACKNOWLEDGE)) {
            aeth = be32_to_cpu(ohdr->u.aeth);
            if ((aeth >> 29) == 0)
                qib_get_credit(qp, aeth);
        }
        goto ack_done;
    }

    /*
     * Skip everything other than the PSN we expect, if we are waiting
     * for a reply to a restarted RDMA read or atomic op.
     */
    if (qp->r_flags & QIB_R_RDMAR_SEQ) {
        if (qib_cmp24(psn, qp->s_last_psn + 1) != 0)
            goto ack_done;
        qp->r_flags &= ~QIB_R_RDMAR_SEQ;
    }

    if (unlikely(qp->s_acked == qp->s_tail))
        goto ack_done;
    wqe = get_swqe_ptr(qp, qp->s_acked);
    status = IB_WC_SUCCESS;

    switch (opcode) {
    case OP(ACKNOWLEDGE):
    case OP(ATOMIC_ACKNOWLEDGE):
    case OP(RDMA_READ_RESPONSE_FIRST):
        aeth = be32_to_cpu(ohdr->u.aeth);
        if (opcode == OP(ATOMIC_ACKNOWLEDGE)) {
            __be32 *p = ohdr->u.at.atomic_ack_eth;

            val = ((u64) be32_to_cpu(p[0]) << 32) |
                be32_to_cpu(p[1]);
        } else
            val = 0;
        if (!do_rc_ack(qp, aeth, psn, opcode, val, rcd) ||
            opcode != OP(RDMA_READ_RESPONSE_FIRST))
            goto ack_done;
        hdrsize += 4;
        wqe = get_swqe_ptr(qp, qp->s_acked);
        if (unlikely(wqe->wr.opcode != IB_WR_RDMA_READ))
            goto ack_op_err;
        /*
         * If this is a response to a resent RDMA read, we
         * have to be careful to copy the data to the right
         * location.
         */
        qp->s_rdma_read_len = restart_sge(&qp->s_rdma_read_sge,
                          wqe, psn, pmtu);
        goto read_middle;

    case OP(RDMA_READ_RESPONSE_MIDDLE):
        /* no AETH, no ACK */
        if (unlikely(qib_cmp24(psn, qp->s_last_psn + 1)))
            goto ack_seq_err;
        if (unlikely(wqe->wr.opcode != IB_WR_RDMA_READ))
            goto ack_op_err;
read_middle:
        if (unlikely(tlen != (hdrsize + pmtu + 4)))
            goto ack_len_err;
        if (unlikely(pmtu >= qp->s_rdma_read_len))
            goto ack_len_err;

        /*
         * We got a response so update the timeout.
         * 4.096 usec. * (1 << qp->timeout)
         */
        qp->s_flags |= QIB_S_TIMER;
        mod_timer(&qp->s_timer, jiffies + qp->timeout_jiffies);
        if (qp->s_flags & QIB_S_WAIT_ACK) {
            qp->s_flags &= ~QIB_S_WAIT_ACK;
            qib_schedule_send(qp);
        }

        if (opcode == OP(RDMA_READ_RESPONSE_MIDDLE))
            qp->s_retry = qp->s_retry_cnt;

        /*
         * Update the RDMA receive state but do the copy w/o
         * holding the locks and blocking interrupts.
         */
        qp->s_rdma_read_len -= pmtu;
        update_last_psn(qp, psn);
        spin_unlock_irqrestore(&qp->s_lock, flags);
        qib_copy_sge(&qp->s_rdma_read_sge, data, pmtu, 0);
        goto bail;

    case OP(RDMA_READ_RESPONSE_ONLY):
        aeth = be32_to_cpu(ohdr->u.aeth);
        if (!do_rc_ack(qp, aeth, psn, opcode, 0, rcd))
            goto ack_done;
        /* Get the number of bytes the message was padded by. */
        pad = (be32_to_cpu(ohdr->bth[0]) >> 20) & 3;
        /*
         * Check that the data size is >= 0 && <= pmtu.
         * Remember to account for the AETH header (4) and
         * ICRC (4).
         */
        if (unlikely(tlen < (hdrsize + pad + 8)))
            goto ack_len_err;
        /*
         * If this is a response to a resent RDMA read, we
         * have to be careful to copy the data to the right
         * location.
         */
        wqe = get_swqe_ptr(qp, qp->s_acked);
        qp->s_rdma_read_len = restart_sge(&qp->s_rdma_read_sge,
                          wqe, psn, pmtu);
        goto read_last;

    case OP(RDMA_READ_RESPONSE_LAST):
        /* ACKs READ req. */
        if (unlikely(qib_cmp24(psn, qp->s_last_psn + 1)))
            goto ack_seq_err;
        if (unlikely(wqe->wr.opcode != IB_WR_RDMA_READ))
            goto ack_op_err;
        /* Get the number of bytes the message was padded by. */
        pad = (be32_to_cpu(ohdr->bth[0]) >> 20) & 3;
        /*
         * Check that the data size is >= 1 && <= pmtu.
         * Remember to account for the AETH header (4) and
         * ICRC (4).
         */
        if (unlikely(tlen <= (hdrsize + pad + 8)))
            goto ack_len_err;
read_last:
        tlen -= hdrsize + pad + 8;
        if (unlikely(tlen != qp->s_rdma_read_len))
            goto ack_len_err;
        aeth = be32_to_cpu(ohdr->u.aeth);
        qib_copy_sge(&qp->s_rdma_read_sge, data, tlen, 0);
        WARN_ON(qp->s_rdma_read_sge.num_sge);
        (void) do_rc_ack(qp, aeth, psn,
                 OP(RDMA_READ_RESPONSE_LAST), 0, rcd);
        goto ack_done;
    }

ack_op_err:
    status = IB_WC_LOC_QP_OP_ERR;
    goto ack_err;

ack_seq_err:
    rdma_seq_err(qp, ibp, psn, rcd);
    goto ack_done;

ack_len_err:
    status = IB_WC_LOC_LEN_ERR;
ack_err:
    if (qp->s_last == qp->s_acked) {
        qib_send_complete(qp, wqe, status);
        qib_error_qp(qp, IB_WC_WR_FLUSH_ERR);
    }
ack_done:
    spin_unlock_irqrestore(&qp->s_lock, flags);
bail:
    return;
}

static int qib_rc_rcv_error(struct qib_other_headers *ohdr,
                void *data,
                struct qib_qp *qp,
                u32 opcode,
                u32 psn,
                int diff,
                struct qib_ctxtdata *rcd)
{
    struct qib_ibport *ibp = to_iport(qp->ibqp.device, qp->port_num);
    struct qib_ack_entry *e;
    unsigned long flags;
    u8 i, prev;
    int old_req;

    if (diff > 0) {
        /*
         * Packet sequence error.
         * A NAK will ACK earlier sends and RDMA writes.
         * Don't queue the NAK if we already sent one.
         */
        if (!qp->r_nak_state) {
            ibp->n_rc_seqnak++;
            qp->r_nak_state = IB_NAK_PSN_ERROR;
            /* Use the expected PSN. */
            qp->r_ack_psn = qp->r_psn;
            /*
             * Wait to send the sequence NAK until all packets
             * in the receive queue have been processed.
             * Otherwise, we end up propagating congestion.
             */
            if (list_empty(&qp->rspwait)) {
                qp->r_flags |= QIB_R_RSP_NAK;
                atomic_inc(&qp->refcount);
                list_add_tail(&qp->rspwait, &rcd->qp_wait_list);
            }
        }
        goto done;
    }

    /*
     * Handle a duplicate request.  Don't re-execute SEND, RDMA
     * write or atomic op.  Don't NAK errors, just silently drop
     * the duplicate request.  Note that r_sge, r_len, and
     * r_rcv_len may be in use so don't modify them.
     *
     * We are supposed to ACK the earliest duplicate PSN but we
     * can coalesce an outstanding duplicate ACK.  We have to
     * send the earliest so that RDMA reads can be restarted at
     * the requester's expected PSN.
     *
     * First, find where this duplicate PSN falls within the
     * ACKs previously sent.
     * old_req is true if there is an older response that is scheduled
     * to be sent before sending this one.
     */
    e = NULL;
    old_req = 1;
    ibp->n_rc_dupreq++;

    spin_lock_irqsave(&qp->s_lock, flags);

    for (i = qp->r_head_ack_queue; ; i = prev) {
        if (i == qp->s_tail_ack_queue)
            old_req = 0;
        if (i)
            prev = i - 1;
        else
            prev = QIB_MAX_RDMA_ATOMIC;
        if (prev == qp->r_head_ack_queue) {
            e = NULL;
            break;
        }
        e = &qp->s_ack_queue[prev];
        if (!e->opcode) {
            e = NULL;
            break;
        }
        if (qib_cmp24(psn, e->psn) >= 0) {
            if (prev == qp->s_tail_ack_queue &&
                qib_cmp24(psn, e->lpsn) <= 0)
                old_req = 0;
            break;
        }
    }
    switch (opcode) {
    case OP(RDMA_READ_REQUEST): {
        struct ib_reth *reth;
        u32 offset;
        u32 len;

        /*
         * If we didn't find the RDMA read request in the ack queue,
         * we can ignore this request.
         */
        if (!e || e->opcode != OP(RDMA_READ_REQUEST))
            goto unlock_done;
        /* RETH comes after BTH */
        reth = &ohdr->u.rc.reth;
        /*
         * Address range must be a subset of the original
         * request and start on pmtu boundaries.
         * We reuse the old ack_queue slot since the requester
         * should not back up and request an earlier PSN for the
         * same request.
         */
        offset = ((psn - e->psn) & QIB_PSN_MASK) *
            qp->pmtu;
        len = be32_to_cpu(reth->length);
        if (unlikely(offset + len != e->rdma_sge.sge_length))
            goto unlock_done;
        if (e->rdma_sge.mr) {
            qib_put_mr(e->rdma_sge.mr);
            e->rdma_sge.mr = NULL;
        }
        if (len != 0) {
            u32 rkey = be32_to_cpu(reth->rkey);
            u64 vaddr = be64_to_cpu(reth->vaddr);
            int ok;

            ok = qib_rkey_ok(qp, &e->rdma_sge, len, vaddr, rkey,
                     IB_ACCESS_REMOTE_READ);
            if (unlikely(!ok))
                goto unlock_done;
        } else {
            e->rdma_sge.vaddr = NULL;
            e->rdma_sge.length = 0;
            e->rdma_sge.sge_length = 0;
        }
        e->psn = psn;
        if (old_req)
            goto unlock_done;
        qp->s_tail_ack_queue = prev;
        break;
    }

    case OP(COMPARE_SWAP):
    case OP(FETCH_ADD): {
        /*
         * If we didn't find the atomic request in the ack queue
         * or the send tasklet is already backed up to send an
         * earlier entry, we can ignore this request.
         */
        if (!e || e->opcode != (u8) opcode || old_req)
            goto unlock_done;
        qp->s_tail_ack_queue = prev;
        break;
    }

    default:
        /*
         * Ignore this operation if it doesn't request an ACK
         * or an earlier RDMA read or atomic is going to be resent.
         */
        if (!(psn & IB_BTH_REQ_ACK) || old_req)
            goto unlock_done;
        /*
         * Resend the most recent ACK if this request is
         * after all the previous RDMA reads and atomics.
         */
        if (i == qp->r_head_ack_queue) {
            spin_unlock_irqrestore(&qp->s_lock, flags);
            qp->r_nak_state = 0;
            qp->r_ack_psn = qp->r_psn - 1;
            goto send_ack;
        }
        /*
         * Try to send a simple ACK to work around a Mellanox bug
         * which doesn't accept a RDMA read response or atomic
         * response as an ACK for earlier SENDs or RDMA writes.
         */
        if (!(qp->s_flags & QIB_S_RESP_PENDING)) {
            spin_unlock_irqrestore(&qp->s_lock, flags);
            qp->r_nak_state = 0;
            qp->r_ack_psn = qp->s_ack_queue[i].psn - 1;
            goto send_ack;
        }
        /*
         * Resend the RDMA read or atomic op which
         * ACKs this duplicate request.
         */
        qp->s_tail_ack_queue = i;
        break;
    }
    qp->s_ack_state = OP(ACKNOWLEDGE);
    qp->s_flags |= QIB_S_RESP_PENDING;
    qp->r_nak_state = 0;
    qib_schedule_send(qp);

unlock_done:
    spin_unlock_irqrestore(&qp->s_lock, flags);
done:
    return 1;

send_ack:
    return 0;
}

void qib_rc_error(struct qib_qp *qp, enum ib_wc_status err)
{
    unsigned long flags;
    int lastwqe;

    spin_lock_irqsave(&qp->s_lock, flags);
    lastwqe = qib_error_qp(qp, err);
    spin_unlock_irqrestore(&qp->s_lock, flags);

    if (lastwqe) {
        struct ib_event ev;

        ev.device = qp->ibqp.device;
        ev.element.qp = &qp->ibqp;
        ev.event = IB_EVENT_QP_LAST_WQE_REACHED;
        qp->ibqp.event_handler(&ev, qp->ibqp.qp_context);
    }
}

static inline void qib_update_ack_queue(struct qib_qp *qp, unsigned n)
{
    unsigned next;

    next = n + 1;
    if (next > QIB_MAX_RDMA_ATOMIC)
        next = 0;
    qp->s_tail_ack_queue = next;
    qp->s_ack_state = OP(ACKNOWLEDGE);
}

void qib_rc_rcv(struct qib_ctxtdata *rcd, struct qib_ib_header *hdr,
        int has_grh, void *data, u32 tlen, struct qib_qp *qp)
{
    struct qib_ibport *ibp = &rcd->ppd->ibport_data;
    struct qib_other_headers *ohdr;
    u32 opcode;
    u32 hdrsize;
    u32 psn;
    u32 pad;
    struct ib_wc wc;
    u32 pmtu = qp->pmtu;
    int diff;
    struct ib_reth *reth;
    unsigned long flags;
    int ret;

    /* Check for GRH */
    if (!has_grh) {
        ohdr = &hdr->u.oth;
        hdrsize = 8 + 12;       /* LRH + BTH */
    } else {
        ohdr = &hdr->u.l.oth;
        hdrsize = 8 + 40 + 12;  /* LRH + GRH + BTH */
    }

    opcode = be32_to_cpu(ohdr->bth[0]);
    if (qib_ruc_check_hdr(ibp, hdr, has_grh, qp, opcode))
        return;

    psn = be32_to_cpu(ohdr->bth[2]);
    opcode >>= 24;

    /*
     * Process responses (ACKs) before anything else.  Note that the
     * packet sequence number will be for something in the send work
     * queue rather than the expected receive packet sequence number.
     * In other words, this QP is the requester.
     */
    if (opcode >= OP(RDMA_READ_RESPONSE_FIRST) &&
        opcode <= OP(ATOMIC_ACKNOWLEDGE)) {
        qib_rc_rcv_resp(ibp, ohdr, data, tlen, qp, opcode, psn,
                hdrsize, pmtu, rcd);
        return;
    }

    /* Compute 24 bits worth of difference. */
    diff = qib_cmp24(psn, qp->r_psn);
    if (unlikely(diff)) {
        if (qib_rc_rcv_error(ohdr, data, qp, opcode, psn, diff, rcd))
            return;
        goto send_ack;
    }

    /* Check for opcode sequence errors. */
    switch (qp->r_state) {
    case OP(SEND_FIRST):
    case OP(SEND_MIDDLE):
        if (opcode == OP(SEND_MIDDLE) ||
            opcode == OP(SEND_LAST) ||
            opcode == OP(SEND_LAST_WITH_IMMEDIATE))
            break;
        goto nack_inv;

    case OP(RDMA_WRITE_FIRST):
    case OP(RDMA_WRITE_MIDDLE):
        if (opcode == OP(RDMA_WRITE_MIDDLE) ||
            opcode == OP(RDMA_WRITE_LAST) ||
            opcode == OP(RDMA_WRITE_LAST_WITH_IMMEDIATE))
            break;
        goto nack_inv;

    default:
        if (opcode == OP(SEND_MIDDLE) ||
            opcode == OP(SEND_LAST) ||
            opcode == OP(SEND_LAST_WITH_IMMEDIATE) ||
            opcode == OP(RDMA_WRITE_MIDDLE) ||
            opcode == OP(RDMA_WRITE_LAST) ||
            opcode == OP(RDMA_WRITE_LAST_WITH_IMMEDIATE))
            goto nack_inv;
        /*
         * Note that it is up to the requester to not send a new
         * RDMA read or atomic operation before receiving an ACK
         * for the previous operation.
         */
        break;
    }

    if (qp->state == IB_QPS_RTR && !(qp->r_flags & QIB_R_COMM_EST)) {
        qp->r_flags |= QIB_R_COMM_EST;
        if (qp->ibqp.event_handler) {
            struct ib_event ev;

            ev.device = qp->ibqp.device;
            ev.element.qp = &qp->ibqp;
            ev.event = IB_EVENT_COMM_EST;
            qp->ibqp.event_handler(&ev, qp->ibqp.qp_context);
        }
    }

    /* OK, process the packet. */
    switch (opcode) {
    case OP(SEND_FIRST):
        ret = qib_get_rwqe(qp, 0);
        if (ret < 0)
            goto nack_op_err;
        if (!ret)
            goto rnr_nak;
        qp->r_rcv_len = 0;
        /* FALLTHROUGH */
    case OP(SEND_MIDDLE):
    case OP(RDMA_WRITE_MIDDLE):
send_middle:
        /* Check for invalid length PMTU or posted rwqe len. */
        if (unlikely(tlen != (hdrsize + pmtu + 4)))
            goto nack_inv;
        qp->r_rcv_len += pmtu;
        if (unlikely(qp->r_rcv_len > qp->r_len))
            goto nack_inv;
        qib_copy_sge(&qp->r_sge, data, pmtu, 1);
        break;

    case OP(RDMA_WRITE_LAST_WITH_IMMEDIATE):
        /* consume RWQE */
        ret = qib_get_rwqe(qp, 1);
        if (ret < 0)
            goto nack_op_err;
        if (!ret)
            goto rnr_nak;
        goto send_last_imm;

    case OP(SEND_ONLY):
    case OP(SEND_ONLY_WITH_IMMEDIATE):
        ret = qib_get_rwqe(qp, 0);
        if (ret < 0)
            goto nack_op_err;
        if (!ret)
            goto rnr_nak;
        qp->r_rcv_len = 0;
        if (opcode == OP(SEND_ONLY))
            goto no_immediate_data;
        /* FALLTHROUGH for SEND_ONLY_WITH_IMMEDIATE */
    case OP(SEND_LAST_WITH_IMMEDIATE):
send_last_imm:
        wc.ex.imm_data = ohdr->u.imm_data;
        hdrsize += 4;
        wc.wc_flags = IB_WC_WITH_IMM;
        goto send_last;
    case OP(SEND_LAST):
    case OP(RDMA_WRITE_LAST):
no_immediate_data:
        wc.wc_flags = 0;
        wc.ex.imm_data = 0;
send_last:
        /* Get the number of bytes the message was padded by. */
        pad = (be32_to_cpu(ohdr->bth[0]) >> 20) & 3;
        /* Check for invalid length. */
        /* XXX LAST len should be >= 1 */
        if (unlikely(tlen < (hdrsize + pad + 4)))
            goto nack_inv;
        /* Don't count the CRC. */
        tlen -= (hdrsize + pad + 4);
        wc.byte_len = tlen + qp->r_rcv_len;
        if (unlikely(wc.byte_len > qp->r_len))
            goto nack_inv;
        qib_copy_sge(&qp->r_sge, data, tlen, 1);
        qib_put_ss(&qp->r_sge);
        qp->r_msn++;
        if (!test_and_clear_bit(QIB_R_WRID_VALID, &qp->r_aflags))
            break;
        wc.wr_id = qp->r_wr_id;
        wc.status = IB_WC_SUCCESS;
        if (opcode == OP(RDMA_WRITE_LAST_WITH_IMMEDIATE) ||
            opcode == OP(RDMA_WRITE_ONLY_WITH_IMMEDIATE))
            wc.opcode = IB_WC_RECV_RDMA_WITH_IMM;
        else
            wc.opcode = IB_WC_RECV;
        wc.qp = &qp->ibqp;
        wc.src_qp = qp->remote_qpn;
        wc.slid = qp->remote_ah_attr.dlid;
        wc.sl = qp->remote_ah_attr.sl;
        /* zero fields that are N/A */
        wc.vendor_err = 0;
        wc.pkey_index = 0;
        wc.dlid_path_bits = 0;
        wc.port_num = 0;
        /* Signal completion event if the solicited bit is set. */
        qib_cq_enter(to_icq(qp->ibqp.recv_cq), &wc,
                 (ohdr->bth[0] &
                  cpu_to_be32(IB_BTH_SOLICITED)) != 0);
        break;

    case OP(RDMA_WRITE_FIRST):
    case OP(RDMA_WRITE_ONLY):
    case OP(RDMA_WRITE_ONLY_WITH_IMMEDIATE):
        if (unlikely(!(qp->qp_access_flags & IB_ACCESS_REMOTE_WRITE)))
            goto nack_inv;
        /* consume RWQE */
        reth = &ohdr->u.rc.reth;
        hdrsize += sizeof(*reth);
        qp->r_len = be32_to_cpu(reth->length);
        qp->r_rcv_len = 0;
        qp->r_sge.sg_list = NULL;
        if (qp->r_len != 0) {
            u32 rkey = be32_to_cpu(reth->rkey);
            u64 vaddr = be64_to_cpu(reth->vaddr);
            int ok;

            /* Check rkey & NAK */
            ok = qib_rkey_ok(qp, &qp->r_sge.sge, qp->r_len, vaddr,
                     rkey, IB_ACCESS_REMOTE_WRITE);
            if (unlikely(!ok))
                goto nack_acc;
            qp->r_sge.num_sge = 1;
        } else {
            qp->r_sge.num_sge = 0;
            qp->r_sge.sge.mr = NULL;
            qp->r_sge.sge.vaddr = NULL;
            qp->r_sge.sge.length = 0;
            qp->r_sge.sge.sge_length = 0;
        }
        if (opcode == OP(RDMA_WRITE_FIRST))
            goto send_middle;
        else if (opcode == OP(RDMA_WRITE_ONLY))
            goto no_immediate_data;
        ret = qib_get_rwqe(qp, 1);
        if (ret < 0)
            goto nack_op_err;
        if (!ret)
            goto rnr_nak;
        wc.ex.imm_data = ohdr->u.rc.imm_data;
        hdrsize += 4;
        wc.wc_flags = IB_WC_WITH_IMM;
        goto send_last;

    case OP(RDMA_READ_REQUEST): {
        struct qib_ack_entry *e;
        u32 len;
        u8 next;

        if (unlikely(!(qp->qp_access_flags & IB_ACCESS_REMOTE_READ)))
            goto nack_inv;
        next = qp->r_head_ack_queue + 1;
        /* s_ack_queue is size QIB_MAX_RDMA_ATOMIC+1 so use > not >= */
        if (next > QIB_MAX_RDMA_ATOMIC)
            next = 0;
        spin_lock_irqsave(&qp->s_lock, flags);
        if (unlikely(next == qp->s_tail_ack_queue)) {
            if (!qp->s_ack_queue[next].sent)
                goto nack_inv_unlck;
            qib_update_ack_queue(qp, next);
        }
        e = &qp->s_ack_queue[qp->r_head_ack_queue];
        if (e->opcode == OP(RDMA_READ_REQUEST) && e->rdma_sge.mr) {
            qib_put_mr(e->rdma_sge.mr);
            e->rdma_sge.mr = NULL;
        }
        reth = &ohdr->u.rc.reth;
        len = be32_to_cpu(reth->length);
        if (len) {
            u32 rkey = be32_to_cpu(reth->rkey);
            u64 vaddr = be64_to_cpu(reth->vaddr);
            int ok;

            /* Check rkey & NAK */
            ok = qib_rkey_ok(qp, &e->rdma_sge, len, vaddr,
                     rkey, IB_ACCESS_REMOTE_READ);
            if (unlikely(!ok))
                goto nack_acc_unlck;
            /*
             * Update the next expected PSN.  We add 1 later
             * below, so only add the remainder here.
             */
            if (len > pmtu)
                qp->r_psn += (len - 1) / pmtu;
        } else {
            e->rdma_sge.mr = NULL;
            e->rdma_sge.vaddr = NULL;
            e->rdma_sge.length = 0;
            e->rdma_sge.sge_length = 0;
        }
        e->opcode = opcode;
        e->sent = 0;
        e->psn = psn;
        e->lpsn = qp->r_psn;
        /*
         * We need to increment the MSN here instead of when we
         * finish sending the result since a duplicate request would
         * increment it more than once.
         */
        qp->r_msn++;
        qp->r_psn++;
        qp->r_state = opcode;
        qp->r_nak_state = 0;
        qp->r_head_ack_queue = next;

        /* Schedule the send tasklet. */
        qp->s_flags |= QIB_S_RESP_PENDING;
        qib_schedule_send(qp);

        goto sunlock;
    }

    case OP(COMPARE_SWAP):
    case OP(FETCH_ADD): {
        struct ib_atomic_eth *ateth;
        struct qib_ack_entry *e;
        u64 vaddr;
        atomic64_t *maddr;
        u64 sdata;
        u32 rkey;
        u8 next;

        if (unlikely(!(qp->qp_access_flags & IB_ACCESS_REMOTE_ATOMIC)))
            goto nack_inv;
        next = qp->r_head_ack_queue + 1;
        if (next > QIB_MAX_RDMA_ATOMIC)
            next = 0;
        spin_lock_irqsave(&qp->s_lock, flags);
        if (unlikely(next == qp->s_tail_ack_queue)) {
            if (!qp->s_ack_queue[next].sent)
                goto nack_inv_unlck;
            qib_update_ack_queue(qp, next);
        }
        e = &qp->s_ack_queue[qp->r_head_ack_queue];
        if (e->opcode == OP(RDMA_READ_REQUEST) && e->rdma_sge.mr) {
            qib_put_mr(e->rdma_sge.mr);
            e->rdma_sge.mr = NULL;
        }
        ateth = &ohdr->u.atomic_eth;
        vaddr = ((u64) be32_to_cpu(ateth->vaddr[0]) << 32) |
            be32_to_cpu(ateth->vaddr[1]);
        if (unlikely(vaddr & (sizeof(u64) - 1)))
            goto nack_inv_unlck;
        rkey = be32_to_cpu(ateth->rkey);
        /* Check rkey & NAK */
        if (unlikely(!qib_rkey_ok(qp, &qp->r_sge.sge, sizeof(u64),
                      vaddr, rkey,
                      IB_ACCESS_REMOTE_ATOMIC)))
            goto nack_acc_unlck;
        /* Perform atomic OP and save result. */
        maddr = (atomic64_t *) qp->r_sge.sge.vaddr;
        sdata = be64_to_cpu(ateth->swap_data);
        e->atomic_data = (opcode == OP(FETCH_ADD)) ?
            (u64) atomic64_add_return(sdata, maddr) - sdata :
            (u64) cmpxchg((u64 *) qp->r_sge.sge.vaddr,
                      be64_to_cpu(ateth->compare_data),
                      sdata);
        qib_put_mr(qp->r_sge.sge.mr);
        qp->r_sge.num_sge = 0;
        e->opcode = opcode;
        e->sent = 0;
        e->psn = psn;
        e->lpsn = psn;
        qp->r_msn++;
        qp->r_psn++;
        qp->r_state = opcode;
        qp->r_nak_state = 0;
        qp->r_head_ack_queue = next;

        /* Schedule the send tasklet. */
        qp->s_flags |= QIB_S_RESP_PENDING;
        qib_schedule_send(qp);

        goto sunlock;
    }

    default:
        /* NAK unknown opcodes. */
        goto nack_inv;
    }
    qp->r_psn++;
    qp->r_state = opcode;
    qp->r_ack_psn = psn;
    qp->r_nak_state = 0;
    /* Send an ACK if requested or required. */
    if (psn & (1 << 31))
        goto send_ack;
    return;

rnr_nak:
    qp->r_nak_state = IB_RNR_NAK | qp->r_min_rnr_timer;
    qp->r_ack_psn = qp->r_psn;
    /* Queue RNR NAK for later */
    if (list_empty(&qp->rspwait)) {
        qp->r_flags |= QIB_R_RSP_NAK;
        atomic_inc(&qp->refcount);
        list_add_tail(&qp->rspwait, &rcd->qp_wait_list);
    }
    return;

nack_op_err:
    qib_rc_error(qp, IB_WC_LOC_QP_OP_ERR);
    qp->r_nak_state = IB_NAK_REMOTE_OPERATIONAL_ERROR;
    qp->r_ack_psn = qp->r_psn;
    /* Queue NAK for later */
    if (list_empty(&qp->rspwait)) {
        qp->r_flags |= QIB_R_RSP_NAK;
        atomic_inc(&qp->refcount);
        list_add_tail(&qp->rspwait, &rcd->qp_wait_list);
    }
    return;

nack_inv_unlck:
    spin_unlock_irqrestore(&qp->s_lock, flags);
nack_inv:
    qib_rc_error(qp, IB_WC_LOC_QP_OP_ERR);
    qp->r_nak_state = IB_NAK_INVALID_REQUEST;
    qp->r_ack_psn = qp->r_psn;
    /* Queue NAK for later */
    if (list_empty(&qp->rspwait)) {
        qp->r_flags |= QIB_R_RSP_NAK;
        atomic_inc(&qp->refcount);
        list_add_tail(&qp->rspwait, &rcd->qp_wait_list);
    }
    return;

nack_acc_unlck:
    spin_unlock_irqrestore(&qp->s_lock, flags);
nack_acc:
    qib_rc_error(qp, IB_WC_LOC_PROT_ERR);
    qp->r_nak_state = IB_NAK_REMOTE_ACCESS_ERROR;
    qp->r_ack_psn = qp->r_psn;
send_ack:
    qib_send_rc_ack(qp);
    return;

sunlock:
    spin_unlock_irqrestore(&qp->s_lock, flags);
}