src/gallium/drivers/svga/svga_resource_buffer_upload.c

   1 /**********************************************************
   2  * Copyright 2008-2009 VMware, Inc.  All rights reserved.
   3  *
   4  * Permission is hereby granted, free of charge, to any person
   5  * obtaining a copy of this software and associated documentation
   6  * files (the "Software"), to deal in the Software without
   7  * restriction, including without limitation the rights to use, copy,
   8  * modify, merge, publish, distribute, sublicense, and/or sell copies
   9  * of the Software, and to permit persons to whom the Software is
  10  * furnished to do so, subject to the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  *
  24  **********************************************************/
  25
  26 #include "svga_cmd.h"
  27
  28 #include "pipe/p_state.h"
  29 #include "pipe/p_defines.h"
  30 #include "util/u_inlines.h"
  31 #include "os/os_thread.h"
  32 #include "util/u_math.h"
  33 #include "util/u_memory.h"
  34
  35 #include "svga_context.h"
  36 #include "svga_screen.h"
  37 #include "svga_resource_buffer.h"
  38 #include "svga_resource_buffer_upload.h"
  39 #include "svga_winsys.h"
  40 #include "svga_debug.h"
  41
  42
  43 /**
  44  * Allocate a winsys_buffer (ie. DMA, aka GMR memory).
  45  *
  46  * It will flush and retry in case the first attempt to create a DMA buffer
  47  * fails, so it should not be called from any function involved in flushing
  48  * to avoid recursion.
  49  */
  50 struct svga_winsys_buffer *
  51 svga_winsys_buffer_create( struct svga_context *svga,
  52                            unsigned alignment,
  53                            unsigned usage,
  54                            unsigned size )
  55 {
  56    struct svga_screen *svgascreen = svga_screen(svga->pipe.screen);
  57    struct svga_winsys_screen *sws = svgascreen->sws;
  58    struct svga_winsys_buffer *buf;
  59
  60    /* Just try */
  61    buf = sws->buffer_create(sws, alignment, usage, size);
  62    if (!buf) {
  63       SVGA_DBG(DEBUG_DMA|DEBUG_PERF, "flushing context to find %d bytes GMR\n",
  64                size);
  65
  66       /* Try flushing all pending DMAs */
  67       svga_context_flush(svga, NULL);
  68       buf = sws->buffer_create(sws, alignment, usage, size);
  69    }
  70
  71    return buf;
  72 }
  73
  74
  75 void
  76 svga_buffer_destroy_hw_storage(struct svga_screen *ss, struct svga_buffer *sbuf)
  77 {
  78    struct svga_winsys_screen *sws = ss->sws;
  79
  80    assert(!sbuf->map.count);
  81    assert(sbuf->hwbuf);
  82    if(sbuf->hwbuf) {
  83       sws->buffer_destroy(sws, sbuf->hwbuf);
  84       sbuf->hwbuf = NULL;
  85    }
  86 }
  87
  88
  89
  90 /**
  91  * Allocate DMA'ble storage for the buffer.
  92  *
  93  * Called before mapping a buffer.
  94  */
  95 enum pipe_error
  96 svga_buffer_create_hw_storage(struct svga_screen *ss,
  97                               struct svga_buffer *sbuf)
  98 {
  99    assert(!sbuf->user);
 100
 101    if(!sbuf->hwbuf) {
 102       struct svga_winsys_screen *sws = ss->sws;
 103       unsigned alignment = 16;
 104       unsigned usage = 0;
 105       unsigned size = sbuf->b.b.width0;
 106
 107       sbuf->hwbuf = sws->buffer_create(sws, alignment, usage, size);
 108       if(!sbuf->hwbuf)
 109          return PIPE_ERROR_OUT_OF_MEMORY;
 110
 111       assert(!sbuf->dma.pending);
 112    }
 113
 114    return PIPE_OK;
 115 }
 116
 117
 118
 119 enum pipe_error
 120 svga_buffer_create_host_surface(struct svga_screen *ss,
 121                                 struct svga_buffer *sbuf)
 122 {
 123    assert(!sbuf->user);
 124
 125    if(!sbuf->handle) {
 126       sbuf->key.flags = 0;
 127
 128       sbuf->key.format = SVGA3D_BUFFER;
 129       if(sbuf->b.b.bind & PIPE_BIND_VERTEX_BUFFER)
 130          sbuf->key.flags |= SVGA3D_SURFACE_HINT_VERTEXBUFFER;
 131       if(sbuf->b.b.bind & PIPE_BIND_INDEX_BUFFER)
 132          sbuf->key.flags |= SVGA3D_SURFACE_HINT_INDEXBUFFER;
 133
 134       sbuf->key.size.width = sbuf->b.b.width0;
 135       sbuf->key.size.height = 1;
 136       sbuf->key.size.depth = 1;
 137
 138       sbuf->key.numFaces = 1;
 139       sbuf->key.numMipLevels = 1;
 140       sbuf->key.cachable = 1;
 141
 142       SVGA_DBG(DEBUG_DMA, "surface_create for buffer sz %d\n", sbuf->b.b.width0);
 143
 144       sbuf->handle = svga_screen_surface_create(ss, &sbuf->key);
 145       if(!sbuf->handle)
 146          return PIPE_ERROR_OUT_OF_MEMORY;
 147
 148       /* Always set the discard flag on the first time the buffer is written
 149        * as svga_screen_surface_create might have passed a recycled host
 150        * buffer.
 151        */
 152       sbuf->dma.flags.discard = TRUE;
 153
 154       SVGA_DBG(DEBUG_DMA, "   --> got sid %p sz %d (buffer)\n", sbuf->handle, sbuf->b.b.width0);
 155    }
 156
 157    return PIPE_OK;
 158 }
 159
 160
 161 void
 162 svga_buffer_destroy_host_surface(struct svga_screen *ss,
 163                                  struct svga_buffer *sbuf)
 164 {
 165    if(sbuf->handle) {
 166       SVGA_DBG(DEBUG_DMA, " ungrab sid %p sz %d\n", sbuf->handle, sbuf->b.b.width0);
 167       svga_screen_surface_destroy(ss, &sbuf->key, &sbuf->handle);
 168    }
 169 }
 170
 171
 172 /**
 173  * Variant of SVGA3D_BufferDMA which leaves the copy box temporarily in blank.
 174  */
 175 static enum pipe_error
 176 svga_buffer_upload_command(struct svga_context *svga,
 177                            struct svga_buffer *sbuf)
 178 {
 179    struct svga_winsys_context *swc = svga->swc;
 180    struct svga_winsys_buffer *guest = sbuf->hwbuf;
 181    struct svga_winsys_surface *host = sbuf->handle;
 182    SVGA3dTransferType transfer = SVGA3D_WRITE_HOST_VRAM;
 183    SVGA3dCmdSurfaceDMA *cmd;
 184    uint32 numBoxes = sbuf->map.num_ranges;
 185    SVGA3dCopyBox *boxes;
 186    SVGA3dCmdSurfaceDMASuffix *pSuffix;
 187    unsigned region_flags;
 188    unsigned surface_flags;
 189    struct pipe_resource *dummy;
 190
 191    if(transfer == SVGA3D_WRITE_HOST_VRAM) {
 192       region_flags = SVGA_RELOC_READ;
 193       surface_flags = SVGA_RELOC_WRITE;
 194    }
 195    else if(transfer == SVGA3D_READ_HOST_VRAM) {
 196       region_flags = SVGA_RELOC_WRITE;
 197       surface_flags = SVGA_RELOC_READ;
 198    }
 199    else {
 200       assert(0);
 201       return PIPE_ERROR_BAD_INPUT;
 202    }
 203
 204    assert(numBoxes);
 205
 206    cmd = SVGA3D_FIFOReserve(swc,
 207                             SVGA_3D_CMD_SURFACE_DMA,
 208                             sizeof *cmd + numBoxes * sizeof *boxes + sizeof *pSuffix,
 209                             2);
 210    if(!cmd)
 211       return PIPE_ERROR_OUT_OF_MEMORY;
 212
 213    swc->region_relocation(swc, &cmd->guest.ptr, guest, 0, region_flags);
 214    cmd->guest.pitch = 0;
 215
 216    swc->surface_relocation(swc, &cmd->host.sid, host, surface_flags);
 217    cmd->host.face = 0;
 218    cmd->host.mipmap = 0;
 219
 220    cmd->transfer = transfer;
 221
 222    sbuf->dma.boxes = (SVGA3dCopyBox *)&cmd[1];
 223    sbuf->dma.svga = svga;
 224
 225    /* Increment reference count */
 226    dummy = NULL;
 227    pipe_resource_reference(&dummy, &sbuf->b.b);
 228
 229    pSuffix = (SVGA3dCmdSurfaceDMASuffix *)((uint8_t*)cmd + sizeof *cmd + numBoxes * sizeof *boxes);
 230    pSuffix->suffixSize = sizeof *pSuffix;
 231    pSuffix->maximumOffset = sbuf->b.b.width0;
 232    pSuffix->flags = sbuf->dma.flags;
 233
 234    SVGA_FIFOCommitAll(swc);
 235
 236    sbuf->dma.flags.discard = FALSE;
 237
 238    return PIPE_OK;
 239 }
 240
 241
 242 /**
 243  * Patch up the upload DMA command reserved by svga_buffer_upload_command
 244  * with the final ranges.
 245  */
 246 void
 247 svga_buffer_upload_flush(struct svga_context *svga,
 248                          struct svga_buffer *sbuf)
 249 {
 250    SVGA3dCopyBox *boxes;
 251    unsigned i;
 252    struct pipe_resource *dummy;
 253
 254    if (!sbuf->dma.pending) {
 255       return;
 256    }
 257
 258    assert(sbuf->handle);
 259    assert(sbuf->hwbuf);
 260    assert(sbuf->map.num_ranges);
 261    assert(sbuf->dma.svga == svga);
 262    assert(sbuf->dma.boxes);
 263
 264    /*
 265     * Patch the DMA command with the final copy box.
 266     */
 267
 268    SVGA_DBG(DEBUG_DMA, "dma to sid %p\n", sbuf->handle);
 269
 270    boxes = sbuf->dma.boxes;
 271    for(i = 0; i < sbuf->map.num_ranges; ++i) {
 272       SVGA_DBG(DEBUG_DMA, "  bytes %u - %u\n",
 273                sbuf->map.ranges[i].start, sbuf->map.ranges[i].end);
 274
 275       boxes[i].x = sbuf->map.ranges[i].start;
 276       boxes[i].y = 0;
 277       boxes[i].z = 0;
 278       boxes[i].w = sbuf->map.ranges[i].end - sbuf->map.ranges[i].start;
 279       boxes[i].h = 1;
 280       boxes[i].d = 1;
 281       boxes[i].srcx = sbuf->map.ranges[i].start;
 282       boxes[i].srcy = 0;
 283       boxes[i].srcz = 0;
 284    }
 285
 286    sbuf->map.num_ranges = 0;
 287
 288    assert(sbuf->head.prev && sbuf->head.next);
 289    LIST_DEL(&sbuf->head);
 290 #ifdef DEBUG
 291    sbuf->head.next = sbuf->head.prev = NULL;
 292 #endif
 293    sbuf->dma.pending = FALSE;
 294    sbuf->dma.flags.discard = FALSE;
 295    sbuf->dma.flags.unsynchronized = FALSE;
 296
 297    sbuf->dma.svga = NULL;
 298    sbuf->dma.boxes = NULL;
 299
 300    /* Decrement reference count (and potentially destroy) */
 301    dummy = &sbuf->b.b;
 302    pipe_resource_reference(&dummy, NULL);
 303 }
 304
 305
 306 /**
 307  * Note a dirty range.
 308  *
 309  * This function only notes the range down. It doesn't actually emit a DMA
 310  * upload command. That only happens when a context tries to refer to this
 311  * buffer, and the DMA upload command is added to that context's command buffer.
 312  *
 313  * We try to lump as many contiguous DMA transfers together as possible.
 314  */
 315 void
 316 svga_buffer_add_range(struct svga_buffer *sbuf,
 317                       unsigned start,
 318                       unsigned end)
 319 {
 320    unsigned i;
 321    unsigned nearest_range;
 322    unsigned nearest_dist;
 323
 324    assert(end > start);
 325
 326    if (sbuf->map.num_ranges < SVGA_BUFFER_MAX_RANGES) {
 327       nearest_range = sbuf->map.num_ranges;
 328       nearest_dist = ~0;
 329    } else {
 330       nearest_range = SVGA_BUFFER_MAX_RANGES - 1;
 331       nearest_dist = 0;
 332    }
 333
 334    /*
 335     * Try to grow one of the ranges.
 336     */
 337
 338    for(i = 0; i < sbuf->map.num_ranges; ++i) {
 339       int left_dist;
 340       int right_dist;
 341       int dist;
 342
 343       left_dist = start - sbuf->map.ranges[i].end;
 344       right_dist = sbuf->map.ranges[i].start - end;
 345       dist = MAX2(left_dist, right_dist);
 346
 347       if (dist <= 0) {
 348          /*
 349           * Ranges are contiguous or overlapping -- extend this one and return.
 350           *
 351           * Note that it is not this function's task to prevent overlapping
 352           * ranges, as the GMR was already given so it is too late to do
 353           * anything.  If the ranges overlap here it must surely be because
 354           * PIPE_TRANSFER_UNSYNCHRONIZED was set.
 355           */
 356
 357          sbuf->map.ranges[i].start = MIN2(sbuf->map.ranges[i].start, start);
 358          sbuf->map.ranges[i].end   = MAX2(sbuf->map.ranges[i].end,   end);
 359          return;
 360       }
 361       else {
 362          /*
 363           * Discontiguous ranges -- keep track of the nearest range.
 364           */
 365
 366          if (dist < nearest_dist) {
 367             nearest_range = i;
 368             nearest_dist = dist;
 369          }
 370       }
 371    }
 372
 373    /*
 374     * We cannot add a new range to an existing DMA command, so patch-up the
 375     * pending DMA upload and start clean.
 376     */
 377
 378    svga_buffer_upload_flush(sbuf->dma.svga, sbuf);
 379
 380    assert(!sbuf->dma.pending);
 381    assert(!sbuf->dma.svga);
 382    assert(!sbuf->dma.boxes);
 383
 384    if (sbuf->map.num_ranges < SVGA_BUFFER_MAX_RANGES) {
 385       /*
 386        * Add a new range.
 387        */
 388
 389       sbuf->map.ranges[sbuf->map.num_ranges].start = start;
 390       sbuf->map.ranges[sbuf->map.num_ranges].end = end;
 391       ++sbuf->map.num_ranges;
 392    } else {
 393       /*
 394        * Everything else failed, so just extend the nearest range.
 395        *
 396        * It is OK to do this because we always keep a local copy of the
 397        * host buffer data, for SW TNL, and the host never modifies the buffer.
 398        */
 399
 400       assert(nearest_range < SVGA_BUFFER_MAX_RANGES);
 401       assert(nearest_range < sbuf->map.num_ranges);
 402       sbuf->map.ranges[nearest_range].start = MIN2(sbuf->map.ranges[nearest_range].start, start);
 403       sbuf->map.ranges[nearest_range].end   = MAX2(sbuf->map.ranges[nearest_range].end,   end);
 404    }
 405 }
 406
 407
 408
 409 /**
 410  * Copy the contents of the malloc buffer to a hardware buffer.
 411  */
 412 static INLINE enum pipe_error
 413 svga_buffer_update_hw(struct svga_screen *ss, struct svga_buffer *sbuf)
 414 {
 415    assert(!sbuf->user);
 416    if(!sbuf->hwbuf) {
 417       enum pipe_error ret;
 418       void *map;
 419
 420       assert(sbuf->swbuf);
 421       if(!sbuf->swbuf)
 422          return PIPE_ERROR;
 423
 424       ret = svga_buffer_create_hw_storage(ss, sbuf);
 425       if(ret != PIPE_OK)
 426          return ret;
 427
 428       pipe_mutex_lock(ss->swc_mutex);
 429       map = ss->sws->buffer_map(ss->sws, sbuf->hwbuf, PIPE_TRANSFER_WRITE);
 430       assert(map);
 431       if(!map) {
 432          pipe_mutex_unlock(ss->swc_mutex);
 433          svga_buffer_destroy_hw_storage(ss, sbuf);
 434          return PIPE_ERROR;
 435       }
 436
 437       memcpy(map, sbuf->swbuf, sbuf->b.b.width0);
 438       ss->sws->buffer_unmap(ss->sws, sbuf->hwbuf);
 439
 440       /* This user/malloc buffer is now indistinguishable from a gpu buffer */
 441       assert(!sbuf->map.count);
 442       if(!sbuf->map.count) {
 443          if(sbuf->user)
 444             sbuf->user = FALSE;
 445          else
 446             align_free(sbuf->swbuf);
 447          sbuf->swbuf = NULL;
 448       }
 449
 450       pipe_mutex_unlock(ss->swc_mutex);
 451    }
 452
 453    return PIPE_OK;
 454 }
 455
 456
 457 /**
 458  * Upload the buffer to the host in a piecewise fashion.
 459  *
 460  * Used when the buffer is too big to fit in the GMR aperture.
 461  */
 462 static INLINE enum pipe_error
 463 svga_buffer_upload_piecewise(struct svga_screen *ss,
 464                              struct svga_context *svga,
 465                              struct svga_buffer *sbuf)
 466 {
 467    struct svga_winsys_screen *sws = ss->sws;
 468    const unsigned alignment = sizeof(void *);
 469    const unsigned usage = 0;
 470    unsigned i;
 471
 472    assert(sbuf->map.num_ranges);
 473    assert(!sbuf->dma.pending);
 474
 475    SVGA_DBG(DEBUG_DMA, "dma to sid %p\n", sbuf->handle);
 476
 477    for (i = 0; i < sbuf->map.num_ranges; ++i) {
 478       struct svga_buffer_range *range = &sbuf->map.ranges[i];
 479       unsigned offset = range->start;
 480       unsigned size = range->end - range->start;
 481
 482       while (offset < range->end) {
 483          struct svga_winsys_buffer *hwbuf;
 484          uint8_t *map;
 485          enum pipe_error ret;
 486
 487          if (offset + size > range->end)
 488             size = range->end - offset;
 489
 490          hwbuf = sws->buffer_create(sws, alignment, usage, size);
 491          while (!hwbuf) {
 492             size /= 2;
 493             if (!size)
 494                return PIPE_ERROR_OUT_OF_MEMORY;
 495             hwbuf = sws->buffer_create(sws, alignment, usage, size);
 496          }
 497
 498          SVGA_DBG(DEBUG_DMA, "  bytes %u - %u\n",
 499                   offset, offset + size);
 500
 501          map = sws->buffer_map(sws, hwbuf,
 502                                PIPE_TRANSFER_WRITE |
 503                                PIPE_TRANSFER_DISCARD);
 504          assert(map);
 505          if (map) {
 506             memcpy(map, sbuf->swbuf, size);
 507             sws->buffer_unmap(sws, hwbuf);
 508          }
 509
 510          ret = SVGA3D_BufferDMA(svga->swc,
 511                                 hwbuf, sbuf->handle,
 512                                 SVGA3D_WRITE_HOST_VRAM,
 513                                 size, 0, offset, sbuf->dma.flags);
 514          if(ret != PIPE_OK) {
 515             svga_context_flush(svga, NULL);
 516             ret =  SVGA3D_BufferDMA(svga->swc,
 517                                     hwbuf, sbuf->handle,
 518                                     SVGA3D_WRITE_HOST_VRAM,
 519                                     size, 0, offset, sbuf->dma.flags);
 520             assert(ret == PIPE_OK);
 521          }
 522
 523          sbuf->dma.flags.discard = FALSE;
 524
 525          sws->buffer_destroy(sws, hwbuf);
 526
 527          offset += size;
 528       }
 529    }
 530
 531    sbuf->map.num_ranges = 0;
 532
 533    return PIPE_OK;
 534 }
 535
 536
 537
 538
 539 /* Get (or create/upload) the winsys surface handle so that we can
 540  * refer to this buffer in fifo commands.
 541  */
 542 struct svga_winsys_surface *
 543 svga_buffer_handle(struct svga_context *svga,
 544                    struct pipe_resource *buf)
 545 {
 546    struct pipe_screen *screen = svga->pipe.screen;
 547    struct svga_screen *ss = svga_screen(screen);
 548    struct svga_buffer *sbuf;
 549    enum pipe_error ret;
 550
 551    if(!buf)
 552       return NULL;
 553
 554    sbuf = svga_buffer(buf);
 555
 556    assert(!sbuf->map.count);
 557    assert(!sbuf->user);
 558
 559    if(!sbuf->handle) {
 560       ret = svga_buffer_create_host_surface(ss, sbuf);
 561       if(ret != PIPE_OK)
 562          return NULL;
 563    }
 564
 565    assert(sbuf->handle);
 566
 567    if (sbuf->map.num_ranges) {
 568       if (!sbuf->dma.pending) {
 569          /*
 570           * No pending DMA upload yet, so insert a DMA upload command now.
 571           */
 572
 573          /*
 574           * Migrate the data from swbuf -> hwbuf if necessary.
 575           */
 576          ret = svga_buffer_update_hw(ss, sbuf);
 577          if (ret == PIPE_OK) {
 578             /*
 579              * Queue a dma command.
 580              */
 581
 582             ret = svga_buffer_upload_command(svga, sbuf);
 583             if (ret == PIPE_ERROR_OUT_OF_MEMORY) {
 584                svga_context_flush(svga, NULL);
 585                ret = svga_buffer_upload_command(svga, sbuf);
 586                assert(ret == PIPE_OK);
 587             }
 588             if (ret == PIPE_OK) {
 589                sbuf->dma.pending = TRUE;
 590                assert(!sbuf->head.prev && !sbuf->head.next);
 591                LIST_ADDTAIL(&sbuf->head, &svga->dirty_buffers);
 592             }
 593          }
 594          else if (ret == PIPE_ERROR_OUT_OF_MEMORY) {
 595             /*
 596              * The buffer is too big to fit in the GMR aperture, so break it in
 597              * smaller pieces.
 598              */
 599             ret = svga_buffer_upload_piecewise(ss, svga, sbuf);
 600          }
 601
 602          if (ret != PIPE_OK) {
 603             /*
 604              * Something unexpected happened above. There is very little that
 605              * we can do other than proceeding while ignoring the dirty ranges.
 606              */
 607             assert(0);
 608             sbuf->map.num_ranges = 0;
 609          }
 610       }
 611       else {
 612          /*
 613           * There a pending dma already. Make sure it is from this context.
 614           */
 615          assert(sbuf->dma.svga == svga);
 616       }
 617    }
 618
 619    assert(!sbuf->map.num_ranges || sbuf->dma.pending);
 620
 621    return sbuf->handle;
 622 }
 623
 624
 625
 626 void
 627 svga_context_flush_buffers(struct svga_context *svga)
 628 {
 629    struct list_head *curr, *next;
 630    struct svga_buffer *sbuf;
 631
 632    curr = svga->dirty_buffers.next;
 633    next = curr->next;
 634    while(curr != &svga->dirty_buffers) {
 635       sbuf = LIST_ENTRY(struct svga_buffer, curr, head);
 636
 637       assert(p_atomic_read(&sbuf->b.b.reference.count) != 0);
 638       assert(sbuf->dma.pending);
 639
 640       svga_buffer_upload_flush(svga, sbuf);
 641
 642       curr = next;
 643       next = curr->next;
 644    }
 645 }
 646
 647
 648 void
 649 svga_redefine_user_buffer(struct pipe_context *pipe,
 650                           struct pipe_resource *resource,
 651                           unsigned offset,
 652                           unsigned size)
 653 {
 654    struct svga_buffer *sbuf = svga_buffer(resource);
 655
 656    assert(sbuf->user);
 657    assert(!sbuf->dma.pending);
 658    assert(!sbuf->handle);
 659    assert(!sbuf->hwbuf);
 660
 661    /*
 662     * We always treat the contents of user-buffers as volatile,
 663     * so no particular action needed here.
 664     */
 665
 666 }