SAFE public projects git trees. - safe/jmp/linux-2.6/blob - drivers/infiniband/hw/ipath/ipath_ud.c

   1 /*
   2  * Copyright (c) 2006 QLogic, Inc. All rights reserved.
   3  * Copyright (c) 2005, 2006 PathScale, Inc. All rights reserved.
   4  *
   5  * This software is available to you under a choice of one of two
   6  * licenses.  You may choose to be licensed under the terms of the GNU
   7  * General Public License (GPL) Version 2, available from the file
   8  * COPYING in the main directory of this source tree, or the
   9  * OpenIB.org BSD license below:
  10  *
  11  *     Redistribution and use in source and binary forms, with or
  12  *     without modification, are permitted provided that the following
  13  *     conditions are met:
  14  *
  15  *      - Redistributions of source code must retain the above
  16  *        copyright notice, this list of conditions and the following
  17  *        disclaimer.
  18  *
  19  *      - Redistributions in binary form must reproduce the above
  20  *        copyright notice, this list of conditions and the following
  21  *        disclaimer in the documentation and/or other materials
  22  *        provided with the distribution.
  23  *
  24  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  25  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  26  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  27  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  28  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  29  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  30  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  31  * SOFTWARE.
  32  */
  33
  34 #include <rdma/ib_smi.h>
  35
  36 #include "ipath_verbs.h"
  37 #include "ips_common.h"
  38
  39 /**
  40  * ipath_ud_loopback - handle send on loopback QPs
  41  * @sqp: the QP
  42  * @ss: the SGE state
  43  * @length: the length of the data to send
  44  * @wr: the work request
  45  * @wc: the work completion entry
  46  *
  47  * This is called from ipath_post_ud_send() to forward a WQE addressed
  48  * to the same HCA.
  49  */
  50 static void ipath_ud_loopback(struct ipath_qp *sqp,
  51                               struct ipath_sge_state *ss,
  52                               u32 length, struct ib_send_wr *wr,
  53                               struct ib_wc *wc)
  54 {
  55         struct ipath_ibdev *dev = to_idev(sqp->ibqp.device);
  56         struct ipath_qp *qp;
  57         struct ib_ah_attr *ah_attr;
  58         unsigned long flags;
  59         struct ipath_rq *rq;
  60         struct ipath_srq *srq;
  61         struct ipath_sge_state rsge;
  62         struct ipath_sge *sge;
  63         struct ipath_rwqe *wqe;
  64
  65         qp = ipath_lookup_qpn(&dev->qp_table, wr->wr.ud.remote_qpn);
  66         if (!qp)
  67                 return;
  68
  69         /*
  70          * Check that the qkey matches (except for QP0, see 9.6.1.4.1).
  71          * Qkeys with the high order bit set mean use the
  72          * qkey from the QP context instead of the WR (see 10.2.5).
  73          */
  74         if (unlikely(qp->ibqp.qp_num &&
  75                      ((int) wr->wr.ud.remote_qkey < 0
  76                       ? qp->qkey : wr->wr.ud.remote_qkey) != qp->qkey)) {
  77                 /* XXX OK to lose a count once in a while. */
  78                 dev->qkey_violations++;
  79                 dev->n_pkt_drops++;
  80                 goto done;
  81         }
  82
  83         /*
  84          * A GRH is expected to preceed the data even if not
  85          * present on the wire.
  86          */
  87         wc->byte_len = length + sizeof(struct ib_grh);
  88
  89         if (wr->opcode == IB_WR_SEND_WITH_IMM) {
  90                 wc->wc_flags = IB_WC_WITH_IMM;
  91                 wc->imm_data = wr->imm_data;
  92         } else {
  93                 wc->wc_flags = 0;
  94                 wc->imm_data = 0;
  95         }
  96
  97         /*
  98          * Get the next work request entry to find where to put the data.
  99          * Note that it is safe to drop the lock after changing rq->tail
 100          * since ipath_post_receive() won't fill the empty slot.
 101          */
 102         if (qp->ibqp.srq) {
 103                 srq = to_isrq(qp->ibqp.srq);
 104                 rq = &srq->rq;
 105         } else {
 106                 srq = NULL;
 107                 rq = &qp->r_rq;
 108         }
 109         spin_lock_irqsave(&rq->lock, flags);
 110         if (rq->tail == rq->head) {
 111                 spin_unlock_irqrestore(&rq->lock, flags);
 112                 dev->n_pkt_drops++;
 113                 goto done;
 114         }
 115         /* Silently drop packets which are too big. */
 116         wqe = get_rwqe_ptr(rq, rq->tail);
 117         if (wc->byte_len > wqe->length) {
 118                 spin_unlock_irqrestore(&rq->lock, flags);
 119                 dev->n_pkt_drops++;
 120                 goto done;
 121         }
 122         wc->wr_id = wqe->wr_id;
 123         rsge.sge = wqe->sg_list[0];
 124         rsge.sg_list = wqe->sg_list + 1;
 125         rsge.num_sge = wqe->num_sge;
 126         if (++rq->tail >= rq->size)
 127                 rq->tail = 0;
 128         if (srq && srq->ibsrq.event_handler) {
 129                 u32 n;
 130
 131                 if (rq->head < rq->tail)
 132                         n = rq->size + rq->head - rq->tail;
 133                 else
 134                         n = rq->head - rq->tail;
 135                 if (n < srq->limit) {
 136                         struct ib_event ev;
 137
 138                         srq->limit = 0;
 139                         spin_unlock_irqrestore(&rq->lock, flags);
 140                         ev.device = qp->ibqp.device;
 141                         ev.element.srq = qp->ibqp.srq;
 142                         ev.event = IB_EVENT_SRQ_LIMIT_REACHED;
 143                         srq->ibsrq.event_handler(&ev,
 144                                                  srq->ibsrq.srq_context);
 145                 } else
 146                         spin_unlock_irqrestore(&rq->lock, flags);
 147         } else
 148                 spin_unlock_irqrestore(&rq->lock, flags);
 149         ah_attr = &to_iah(wr->wr.ud.ah)->attr;
 150         if (ah_attr->ah_flags & IB_AH_GRH) {
 151                 ipath_copy_sge(&rsge, &ah_attr->grh, sizeof(struct ib_grh));
 152                 wc->wc_flags |= IB_WC_GRH;
 153         } else
 154                 ipath_skip_sge(&rsge, sizeof(struct ib_grh));
 155         sge = &ss->sge;
 156         while (length) {
 157                 u32 len = sge->length;
 158
 159                 if (len > length)
 160                         len = length;
 161                 BUG_ON(len == 0);
 162                 ipath_copy_sge(&rsge, sge->vaddr, len);
 163                 sge->vaddr += len;
 164                 sge->length -= len;
 165                 sge->sge_length -= len;
 166                 if (sge->sge_length == 0) {
 167                         if (--ss->num_sge)
 168                                 *sge = *ss->sg_list++;
 169                 } else if (sge->length == 0 && sge->mr != NULL) {
 170                         if (++sge->n >= IPATH_SEGSZ) {
 171                                 if (++sge->m >= sge->mr->mapsz)
 172                                         break;
 173                                 sge->n = 0;
 174                         }
 175                         sge->vaddr =
 176                                 sge->mr->map[sge->m]->segs[sge->n].vaddr;
 177                         sge->length =
 178                                 sge->mr->map[sge->m]->segs[sge->n].length;
 179                 }
 180                 length -= len;
 181         }
 182         wc->status = IB_WC_SUCCESS;
 183         wc->opcode = IB_WC_RECV;
 184         wc->vendor_err = 0;
 185         wc->qp_num = qp->ibqp.qp_num;
 186         wc->src_qp = sqp->ibqp.qp_num;
 187         /* XXX do we know which pkey matched? Only needed for GSI. */
 188         wc->pkey_index = 0;
 189         wc->slid = ipath_layer_get_lid(dev->dd) |
 190                 (ah_attr->src_path_bits &
 191                  ((1 << (dev->mkeyprot_resv_lmc & 7)) - 1));
 192         wc->sl = ah_attr->sl;
 193         wc->dlid_path_bits =
 194                 ah_attr->dlid & ((1 << (dev->mkeyprot_resv_lmc & 7)) - 1);
 195         /* Signal completion event if the solicited bit is set. */
 196         ipath_cq_enter(to_icq(qp->ibqp.recv_cq), wc,
 197                        wr->send_flags & IB_SEND_SOLICITED);
 198
 199 done:
 200         if (atomic_dec_and_test(&qp->refcount))
 201                 wake_up(&qp->wait);
 202 }
 203
 204 /**
 205  * ipath_post_ud_send - post a UD send on QP
 206  * @qp: the QP
 207  * @wr: the work request
 208  *
 209  * Note that we actually send the data as it is posted instead of putting
 210  * the request into a ring buffer.  If we wanted to use a ring buffer,
 211  * we would need to save a reference to the destination address in the SWQE.
 212  */
 213 int ipath_post_ud_send(struct ipath_qp *qp, struct ib_send_wr *wr)
 214 {
 215         struct ipath_ibdev *dev = to_idev(qp->ibqp.device);
 216         struct ipath_other_headers *ohdr;
 217         struct ib_ah_attr *ah_attr;
 218         struct ipath_sge_state ss;
 219         struct ipath_sge *sg_list;
 220         struct ib_wc wc;
 221         u32 hwords;
 222         u32 nwords;
 223         u32 len;
 224         u32 extra_bytes;
 225         u32 bth0;
 226         u16 lrh0;
 227         u16 lid;
 228         int i;
 229         int ret;
 230
 231         if (!(ib_ipath_state_ops[qp->state] & IPATH_PROCESS_SEND_OK)) {
 232                 ret = 0;
 233                 goto bail;
 234         }
 235
 236         /* IB spec says that num_sge == 0 is OK. */
 237         if (wr->num_sge > qp->s_max_sge) {
 238                 ret = -EINVAL;
 239                 goto bail;
 240         }
 241
 242         if (wr->num_sge > 1) {
 243                 sg_list = kmalloc((qp->s_max_sge - 1) * sizeof(*sg_list),
 244                                   GFP_ATOMIC);
 245                 if (!sg_list) {
 246                         ret = -ENOMEM;
 247                         goto bail;
 248                 }
 249         } else
 250                 sg_list = NULL;
 251
 252         /* Check the buffer to send. */
 253         ss.sg_list = sg_list;
 254         ss.sge.mr = NULL;
 255         ss.sge.vaddr = NULL;
 256         ss.sge.length = 0;
 257         ss.sge.sge_length = 0;
 258         ss.num_sge = 0;
 259         len = 0;
 260         for (i = 0; i < wr->num_sge; i++) {
 261                 /* Check LKEY */
 262                 if (to_ipd(qp->ibqp.pd)->user && wr->sg_list[i].lkey == 0) {
 263                         ret = -EINVAL;
 264                         goto bail;
 265                 }
 266
 267                 if (wr->sg_list[i].length == 0)
 268                         continue;
 269                 if (!ipath_lkey_ok(&dev->lk_table, ss.num_sge ?
 270                                    sg_list + ss.num_sge - 1 : &ss.sge,
 271                                    &wr->sg_list[i], 0)) {
 272                         ret = -EINVAL;
 273                         goto bail;
 274                 }
 275                 len += wr->sg_list[i].length;
 276                 ss.num_sge++;
 277         }
 278         extra_bytes = (4 - len) & 3;
 279         nwords = (len + extra_bytes) >> 2;
 280
 281         /* Construct the header. */
 282         ah_attr = &to_iah(wr->wr.ud.ah)->attr;
 283         if (ah_attr->dlid == 0) {
 284                 ret = -EINVAL;
 285                 goto bail;
 286         }
 287         if (ah_attr->dlid >= IPS_MULTICAST_LID_BASE) {
 288                 if (ah_attr->dlid != IPS_PERMISSIVE_LID)
 289                         dev->n_multicast_xmit++;
 290                 else
 291                         dev->n_unicast_xmit++;
 292         } else {
 293                 dev->n_unicast_xmit++;
 294                 lid = ah_attr->dlid &
 295                         ~((1 << (dev->mkeyprot_resv_lmc & 7)) - 1);
 296                 if (unlikely(lid == ipath_layer_get_lid(dev->dd))) {
 297                         /*
 298                          * Pass in an uninitialized ib_wc to save stack
 299                          * space.
 300                          */
 301                         ipath_ud_loopback(qp, &ss, len, wr, &wc);
 302                         goto done;
 303                 }
 304         }
 305         if (ah_attr->ah_flags & IB_AH_GRH) {
 306                 /* Header size in 32-bit words. */
 307                 hwords = 17;
 308                 lrh0 = IPS_LRH_GRH;
 309                 ohdr = &qp->s_hdr.u.l.oth;
 310                 qp->s_hdr.u.l.grh.version_tclass_flow =
 311                         cpu_to_be32((6 << 28) |
 312                                     (ah_attr->grh.traffic_class << 20) |
 313                                     ah_attr->grh.flow_label);
 314                 qp->s_hdr.u.l.grh.paylen =
 315                         cpu_to_be16(((wr->opcode ==
 316                                       IB_WR_SEND_WITH_IMM ? 6 : 5) +
 317                                      nwords + SIZE_OF_CRC) << 2);
 318                 /* next_hdr is defined by C8-7 in ch. 8.4.1 */
 319                 qp->s_hdr.u.l.grh.next_hdr = 0x1B;
 320                 qp->s_hdr.u.l.grh.hop_limit = ah_attr->grh.hop_limit;
 321                 /* The SGID is 32-bit aligned. */
 322                 qp->s_hdr.u.l.grh.sgid.global.subnet_prefix =
 323                         dev->gid_prefix;
 324                 qp->s_hdr.u.l.grh.sgid.global.interface_id =
 325                         ipath_layer_get_guid(dev->dd);
 326                 qp->s_hdr.u.l.grh.dgid = ah_attr->grh.dgid;
 327                 /*
 328                  * Don't worry about sending to locally attached multicast
 329                  * QPs.  It is unspecified by the spec. what happens.
 330                  */
 331         } else {
 332                 /* Header size in 32-bit words. */
 333                 hwords = 7;
 334                 lrh0 = IPS_LRH_BTH;
 335                 ohdr = &qp->s_hdr.u.oth;
 336         }
 337         if (wr->opcode == IB_WR_SEND_WITH_IMM) {
 338                 ohdr->u.ud.imm_data = wr->imm_data;
 339                 wc.imm_data = wr->imm_data;
 340                 hwords += 1;
 341                 bth0 = IB_OPCODE_UD_SEND_ONLY_WITH_IMMEDIATE << 24;
 342         } else if (wr->opcode == IB_WR_SEND) {
 343                 wc.imm_data = 0;
 344                 bth0 = IB_OPCODE_UD_SEND_ONLY << 24;
 345         } else {
 346                 ret = -EINVAL;
 347                 goto bail;
 348         }
 349         lrh0 |= ah_attr->sl << 4;
 350         if (qp->ibqp.qp_type == IB_QPT_SMI)
 351                 lrh0 |= 0xF000; /* Set VL (see ch. 13.5.3.1) */
 352         qp->s_hdr.lrh[0] = cpu_to_be16(lrh0);
 353         qp->s_hdr.lrh[1] = cpu_to_be16(ah_attr->dlid);  /* DEST LID */
 354         qp->s_hdr.lrh[2] = cpu_to_be16(hwords + nwords + SIZE_OF_CRC);
 355         lid = ipath_layer_get_lid(dev->dd);
 356         if (lid) {
 357                 lid |= ah_attr->src_path_bits &
 358                         ((1 << (dev->mkeyprot_resv_lmc & 7)) - 1);
 359                 qp->s_hdr.lrh[3] = cpu_to_be16(lid);
 360         } else
 361                 qp->s_hdr.lrh[3] = IB_LID_PERMISSIVE;
 362         if (wr->send_flags & IB_SEND_SOLICITED)
 363                 bth0 |= 1 << 23;
 364         bth0 |= extra_bytes << 20;
 365         bth0 |= qp->ibqp.qp_type == IB_QPT_SMI ? IPS_DEFAULT_P_KEY :
 366                 ipath_layer_get_pkey(dev->dd, qp->s_pkey_index);
 367         ohdr->bth[0] = cpu_to_be32(bth0);
 368         /*
 369          * Use the multicast QP if the destination LID is a multicast LID.
 370          */
 371         ohdr->bth[1] = ah_attr->dlid >= IPS_MULTICAST_LID_BASE &&
 372                 ah_attr->dlid != IPS_PERMISSIVE_LID ?
 373                 __constant_cpu_to_be32(IPS_MULTICAST_QPN) :
 374                 cpu_to_be32(wr->wr.ud.remote_qpn);
 375         /* XXX Could lose a PSN count but not worth locking */
 376         ohdr->bth[2] = cpu_to_be32(qp->s_next_psn++ & IPS_PSN_MASK);
 377         /*
 378          * Qkeys with the high order bit set mean use the
 379          * qkey from the QP context instead of the WR (see 10.2.5).
 380          */
 381         ohdr->u.ud.deth[0] = cpu_to_be32((int)wr->wr.ud.remote_qkey < 0 ?
 382                                          qp->qkey : wr->wr.ud.remote_qkey);
 383         ohdr->u.ud.deth[1] = cpu_to_be32(qp->ibqp.qp_num);
 384         if (ipath_verbs_send(dev->dd, hwords, (u32 *) &qp->s_hdr,
 385                              len, &ss))
 386                 dev->n_no_piobuf++;
 387
 388 done:
 389         /* Queue the completion status entry. */
 390         if (!test_bit(IPATH_S_SIGNAL_REQ_WR, &qp->s_flags) ||
 391             (wr->send_flags & IB_SEND_SIGNALED)) {
 392                 wc.wr_id = wr->wr_id;
 393                 wc.status = IB_WC_SUCCESS;
 394                 wc.vendor_err = 0;
 395                 wc.opcode = IB_WC_SEND;
 396                 wc.byte_len = len;
 397                 wc.qp_num = qp->ibqp.qp_num;
 398                 wc.src_qp = 0;
 399                 wc.wc_flags = 0;
 400                 /* XXX initialize other fields? */
 401                 ipath_cq_enter(to_icq(qp->ibqp.send_cq), &wc, 0);
 402         }
 403         kfree(sg_list);
 404
 405         ret = 0;
 406
 407 bail:
 408         return ret;
 409 }
 410
 411 /**
 412  * ipath_ud_rcv - receive an incoming UD packet
 413  * @dev: the device the packet came in on
 414  * @hdr: the packet header
 415  * @has_grh: true if the packet has a GRH
 416  * @data: the packet data
 417  * @tlen: the packet length
 418  * @qp: the QP the packet came on
 419  *
 420  * This is called from ipath_qp_rcv() to process an incoming UD packet
 421  * for the given QP.
 422  * Called at interrupt level.
 423  */
 424 void ipath_ud_rcv(struct ipath_ibdev *dev, struct ipath_ib_header *hdr,
 425                   int has_grh, void *data, u32 tlen, struct ipath_qp *qp)
 426 {
 427         struct ipath_other_headers *ohdr;
 428         int opcode;
 429         u32 hdrsize;
 430         u32 pad;
 431         unsigned long flags;
 432         struct ib_wc wc;
 433         u32 qkey;
 434         u32 src_qp;
 435         struct ipath_rq *rq;
 436         struct ipath_srq *srq;
 437         struct ipath_rwqe *wqe;
 438         u16 dlid;
 439         int header_in_data;
 440
 441         /* Check for GRH */
 442         if (!has_grh) {
 443                 ohdr = &hdr->u.oth;
 444                 hdrsize = 8 + 12 + 8;   /* LRH + BTH + DETH */
 445                 qkey = be32_to_cpu(ohdr->u.ud.deth[0]);
 446                 src_qp = be32_to_cpu(ohdr->u.ud.deth[1]);
 447                 header_in_data = 0;
 448         } else {
 449                 ohdr = &hdr->u.l.oth;
 450                 hdrsize = 8 + 40 + 12 + 8; /* LRH + GRH + BTH + DETH */
 451                 /*
 452                  * The header with GRH is 68 bytes and the core driver sets
 453                  * the eager header buffer size to 56 bytes so the last 12
 454                  * bytes of the IB header is in the data buffer.
 455                  */
 456                 header_in_data =
 457                         ipath_layer_get_rcvhdrentsize(dev->dd) == 16;
 458                 if (header_in_data) {
 459                         qkey = be32_to_cpu(((__be32 *) data)[1]);
 460                         src_qp = be32_to_cpu(((__be32 *) data)[2]);
 461                         data += 12;
 462                 } else {
 463                         qkey = be32_to_cpu(ohdr->u.ud.deth[0]);
 464                         src_qp = be32_to_cpu(ohdr->u.ud.deth[1]);
 465                 }
 466         }
 467         src_qp &= IPS_QPN_MASK;
 468
 469         /*
 470          * Check that the permissive LID is only used on QP0
 471          * and the QKEY matches (see 9.6.1.4.1 and 9.6.1.5.1).
 472          */
 473         if (qp->ibqp.qp_num) {
 474                 if (unlikely(hdr->lrh[1] == IB_LID_PERMISSIVE ||
 475                              hdr->lrh[3] == IB_LID_PERMISSIVE)) {
 476                         dev->n_pkt_drops++;
 477                         goto bail;
 478                 }
 479                 if (unlikely(qkey != qp->qkey)) {
 480                         /* XXX OK to lose a count once in a while. */
 481                         dev->qkey_violations++;
 482                         dev->n_pkt_drops++;
 483                         goto bail;
 484                 }
 485         } else if (hdr->lrh[1] == IB_LID_PERMISSIVE ||
 486                    hdr->lrh[3] == IB_LID_PERMISSIVE) {
 487                 struct ib_smp *smp = (struct ib_smp *) data;
 488
 489                 if (smp->mgmt_class != IB_MGMT_CLASS_SUBN_DIRECTED_ROUTE) {
 490                         dev->n_pkt_drops++;
 491                         goto bail;
 492                 }
 493         }
 494
 495         /* Get the number of bytes the message was padded by. */
 496         pad = (be32_to_cpu(ohdr->bth[0]) >> 20) & 3;
 497         if (unlikely(tlen < (hdrsize + pad + 4))) {
 498                 /* Drop incomplete packets. */
 499                 dev->n_pkt_drops++;
 500                 goto bail;
 501         }
 502         tlen -= hdrsize + pad + 4;
 503
 504         /* Drop invalid MAD packets (see 13.5.3.1). */
 505         if (unlikely((qp->ibqp.qp_num == 0 &&
 506                       (tlen != 256 ||
 507                        (be16_to_cpu(hdr->lrh[0]) >> 12) != 15)) ||
 508                      (qp->ibqp.qp_num == 1 &&
 509                       (tlen != 256 ||
 510                        (be16_to_cpu(hdr->lrh[0]) >> 12) == 15)))) {
 511                 dev->n_pkt_drops++;
 512                 goto bail;
 513         }
 514
 515         /*
 516          * A GRH is expected to preceed the data even if not
 517          * present on the wire.
 518          */
 519         wc.byte_len = tlen + sizeof(struct ib_grh);
 520
 521         /*
 522          * The opcode is in the low byte when its in network order
 523          * (top byte when in host order).
 524          */
 525         opcode = be32_to_cpu(ohdr->bth[0]) >> 24;
 526         if (qp->ibqp.qp_num > 1 &&
 527             opcode == IB_OPCODE_UD_SEND_ONLY_WITH_IMMEDIATE) {
 528                 if (header_in_data) {
 529                         wc.imm_data = *(__be32 *) data;
 530                         data += sizeof(__be32);
 531                 } else
 532                         wc.imm_data = ohdr->u.ud.imm_data;
 533                 wc.wc_flags = IB_WC_WITH_IMM;
 534                 hdrsize += sizeof(u32);
 535         } else if (opcode == IB_OPCODE_UD_SEND_ONLY) {
 536                 wc.imm_data = 0;
 537                 wc.wc_flags = 0;
 538         } else {
 539                 dev->n_pkt_drops++;
 540                 goto bail;
 541         }
 542
 543         /*
 544          * Get the next work request entry to find where to put the data.
 545          * Note that it is safe to drop the lock after changing rq->tail
 546          * since ipath_post_receive() won't fill the empty slot.
 547          */
 548         if (qp->ibqp.srq) {
 549                 srq = to_isrq(qp->ibqp.srq);
 550                 rq = &srq->rq;
 551         } else {
 552                 srq = NULL;
 553                 rq = &qp->r_rq;
 554         }
 555         spin_lock_irqsave(&rq->lock, flags);
 556         if (rq->tail == rq->head) {
 557                 spin_unlock_irqrestore(&rq->lock, flags);
 558                 dev->n_pkt_drops++;
 559                 goto bail;
 560         }
 561         /* Silently drop packets which are too big. */
 562         wqe = get_rwqe_ptr(rq, rq->tail);
 563         if (wc.byte_len > wqe->length) {
 564                 spin_unlock_irqrestore(&rq->lock, flags);
 565                 dev->n_pkt_drops++;
 566                 goto bail;
 567         }
 568         wc.wr_id = wqe->wr_id;
 569         qp->r_sge.sge = wqe->sg_list[0];
 570         qp->r_sge.sg_list = wqe->sg_list + 1;
 571         qp->r_sge.num_sge = wqe->num_sge;
 572         if (++rq->tail >= rq->size)
 573                 rq->tail = 0;
 574         if (srq && srq->ibsrq.event_handler) {
 575                 u32 n;
 576
 577                 if (rq->head < rq->tail)
 578                         n = rq->size + rq->head - rq->tail;
 579                 else
 580                         n = rq->head - rq->tail;
 581                 if (n < srq->limit) {
 582                         struct ib_event ev;
 583
 584                         srq->limit = 0;
 585                         spin_unlock_irqrestore(&rq->lock, flags);
 586                         ev.device = qp->ibqp.device;
 587                         ev.element.srq = qp->ibqp.srq;
 588                         ev.event = IB_EVENT_SRQ_LIMIT_REACHED;
 589                         srq->ibsrq.event_handler(&ev,
 590                                                  srq->ibsrq.srq_context);
 591                 } else
 592                         spin_unlock_irqrestore(&rq->lock, flags);
 593         } else
 594                 spin_unlock_irqrestore(&rq->lock, flags);
 595         if (has_grh) {
 596                 ipath_copy_sge(&qp->r_sge, &hdr->u.l.grh,
 597                                sizeof(struct ib_grh));
 598                 wc.wc_flags |= IB_WC_GRH;
 599         } else
 600                 ipath_skip_sge(&qp->r_sge, sizeof(struct ib_grh));
 601         ipath_copy_sge(&qp->r_sge, data,
 602                        wc.byte_len - sizeof(struct ib_grh));
 603         wc.status = IB_WC_SUCCESS;
 604         wc.opcode = IB_WC_RECV;
 605         wc.vendor_err = 0;
 606         wc.qp_num = qp->ibqp.qp_num;
 607         wc.src_qp = src_qp;
 608         /* XXX do we know which pkey matched? Only needed for GSI. */
 609         wc.pkey_index = 0;
 610         wc.slid = be16_to_cpu(hdr->lrh[3]);
 611         wc.sl = (be16_to_cpu(hdr->lrh[0]) >> 4) & 0xF;
 612         dlid = be16_to_cpu(hdr->lrh[1]);
 613         /*
 614          * Save the LMC lower bits if the destination LID is a unicast LID.
 615          */
 616         wc.dlid_path_bits = dlid >= IPS_MULTICAST_LID_BASE ? 0 :
 617                 dlid & ((1 << (dev->mkeyprot_resv_lmc & 7)) - 1);
 618         /* Signal completion event if the solicited bit is set. */
 619         ipath_cq_enter(to_icq(qp->ibqp.recv_cq), &wc,
 620                        (ohdr->bth[0] &
 621                         __constant_cpu_to_be32(1 << 23)) != 0);
 622
 623 bail:;
 624 }