drivers/gpu/drm/ttm/ttm_bo_util.c

   1 /* SPDX-License-Identifier: GPL-2.0 OR MIT */
   2 /**************************************************************************
   3  *
   4  * Copyright (c) 2007-2009 VMware, Inc., Palo Alto, CA., USA
   5  * All Rights Reserved.
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a
   8  * copy of this software and associated documentation files (the
   9  * "Software"), to deal in the Software without restriction, including
  10  * without limitation the rights to use, copy, modify, merge, publish,
  11  * distribute, sub license, and/or sell copies of the Software, and to
  12  * permit persons to whom the Software is furnished to do so, subject to
  13  * the following conditions:
  14  *
  15  * The above copyright notice and this permission notice (including the
  16  * next paragraph) shall be included in all copies or substantial portions
  17  * of the Software.
  18  *
  19  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21  * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
  22  * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM,
  23  * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
  24  * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
  25  * USE OR OTHER DEALINGS IN THE SOFTWARE.
  26  *
  27  **************************************************************************/
  28 /*
  29  * Authors: Thomas Hellstrom <thellstrom-at-vmware-dot-com>
  30  */
  31
  32 #include <drm/ttm/ttm_bo_driver.h>
  33 #include <drm/ttm/ttm_placement.h>
  34 #include <drm/drm_vma_manager.h>
  35 #include <linux/io.h>
  36 #include <linux/highmem.h>
  37 #include <linux/wait.h>
  38 #include <linux/slab.h>
  39 #include <linux/vmalloc.h>
  40 #include <linux/module.h>
  41 #include <linux/dma-resv.h>
  42
  43 struct ttm_transfer_obj {
  44         struct ttm_buffer_object base;
  45         struct ttm_buffer_object *bo;
  46 };
  47
  48 int ttm_bo_move_to_new_tt_mem(struct ttm_buffer_object *bo,
  49                               struct ttm_operation_ctx *ctx,
  50                               struct ttm_resource *new_mem)
  51 {
  52         int ret;
  53
  54         if (new_mem->mem_type == TTM_PL_SYSTEM)
  55                 return 0;
  56
  57         ret = ttm_tt_populate(bo->bdev, bo->ttm, ctx);
  58         if (unlikely(ret != 0))
  59                 return ret;
  60
  61         ret = ttm_bo_tt_bind(bo, new_mem);
  62         if (unlikely(ret != 0))
  63                 return ret;
  64
  65         return 0;
  66 }
  67 EXPORT_SYMBOL(ttm_bo_move_to_new_tt_mem);
  68
  69 static int ttm_bo_move_to_system(struct ttm_buffer_object *bo,
  70                                  struct ttm_operation_ctx *ctx)
  71 {
  72         struct ttm_resource *old_mem = &bo->mem;
  73         int ret;
  74
  75         if (old_mem->mem_type == TTM_PL_SYSTEM)
  76                 return 0;
  77
  78         ret = ttm_bo_wait_ctx(bo, ctx);
  79         if (unlikely(ret != 0)) {
  80                 if (ret != -ERESTARTSYS)
  81                         pr_err("Failed to expire sync object before unbinding TTM\n");
  82                 return ret;
  83         }
  84
  85         ttm_bo_tt_unbind(bo);
  86         ttm_resource_free(bo, &bo->mem);
  87         old_mem->mem_type = TTM_PL_SYSTEM;
  88         return 0;
  89 }
  90
  91 int ttm_bo_move_ttm(struct ttm_buffer_object *bo,
  92                    struct ttm_operation_ctx *ctx,
  93                     struct ttm_resource *new_mem)
  94 {
  95         int ret;
  96
  97         ret = ttm_bo_move_to_system(bo, ctx);
  98         if (unlikely(ret != 0))
  99                 return ret;
 100
 101         ret = ttm_bo_move_to_new_tt_mem(bo, ctx, new_mem);
 102         if (unlikely(ret != 0))
 103                 return ret;
 104
 105         ttm_bo_assign_mem(bo, new_mem);
 106         return 0;
 107 }
 108 EXPORT_SYMBOL(ttm_bo_move_ttm);
 109
 110 int ttm_mem_io_reserve(struct ttm_bo_device *bdev,
 111                        struct ttm_resource *mem)
 112 {
 113         if (mem->bus.offset || mem->bus.addr)
 114                 return 0;
 115
 116         mem->bus.is_iomem = false;
 117         if (!bdev->driver->io_mem_reserve)
 118                 return 0;
 119
 120         return bdev->driver->io_mem_reserve(bdev, mem);
 121 }
 122
 123 void ttm_mem_io_free(struct ttm_bo_device *bdev,
 124                      struct ttm_resource *mem)
 125 {
 126         if (!mem->bus.offset && !mem->bus.addr)
 127                 return;
 128
 129         if (bdev->driver->io_mem_free)
 130                 bdev->driver->io_mem_free(bdev, mem);
 131
 132         mem->bus.offset = 0;
 133         mem->bus.addr = NULL;
 134 }
 135
 136 static int ttm_resource_ioremap(struct ttm_bo_device *bdev,
 137                                struct ttm_resource *mem,
 138                                void **virtual)
 139 {
 140         int ret;
 141         void *addr;
 142
 143         *virtual = NULL;
 144         ret = ttm_mem_io_reserve(bdev, mem);
 145         if (ret || !mem->bus.is_iomem)
 146                 return ret;
 147
 148         if (mem->bus.addr) {
 149                 addr = mem->bus.addr;
 150         } else {
 151                 size_t bus_size = (size_t)mem->num_pages << PAGE_SHIFT;
 152
 153                 if (mem->bus.caching == ttm_write_combined)
 154                         addr = ioremap_wc(mem->bus.offset, bus_size);
 155                 else
 156                         addr = ioremap(mem->bus.offset, bus_size);
 157                 if (!addr) {
 158                         ttm_mem_io_free(bdev, mem);
 159                         return -ENOMEM;
 160                 }
 161         }
 162         *virtual = addr;
 163         return 0;
 164 }
 165
 166 static void ttm_resource_iounmap(struct ttm_bo_device *bdev,
 167                                 struct ttm_resource *mem,
 168                                 void *virtual)
 169 {
 170         if (virtual && mem->bus.addr == NULL)
 171                 iounmap(virtual);
 172         ttm_mem_io_free(bdev, mem);
 173 }
 174
 175 static int ttm_copy_io_page(void *dst, void *src, unsigned long page)
 176 {
 177         uint32_t *dstP =
 178             (uint32_t *) ((unsigned long)dst + (page << PAGE_SHIFT));
 179         uint32_t *srcP =
 180             (uint32_t *) ((unsigned long)src + (page << PAGE_SHIFT));
 181
 182         int i;
 183         for (i = 0; i < PAGE_SIZE / sizeof(uint32_t); ++i)
 184                 iowrite32(ioread32(srcP++), dstP++);
 185         return 0;
 186 }
 187
 188 static int ttm_copy_io_ttm_page(struct ttm_tt *ttm, void *src,
 189                                 unsigned long page,
 190                                 pgprot_t prot)
 191 {
 192         struct page *d = ttm->pages[page];
 193         void *dst;
 194
 195         if (!d)
 196                 return -ENOMEM;
 197
 198         src = (void *)((unsigned long)src + (page << PAGE_SHIFT));
 199         dst = kmap_atomic_prot(d, prot);
 200         if (!dst)
 201                 return -ENOMEM;
 202
 203         memcpy_fromio(dst, src, PAGE_SIZE);
 204
 205         kunmap_atomic(dst);
 206
 207         return 0;
 208 }
 209
 210 static int ttm_copy_ttm_io_page(struct ttm_tt *ttm, void *dst,
 211                                 unsigned long page,
 212                                 pgprot_t prot)
 213 {
 214         struct page *s = ttm->pages[page];
 215         void *src;
 216
 217         if (!s)
 218                 return -ENOMEM;
 219
 220         dst = (void *)((unsigned long)dst + (page << PAGE_SHIFT));
 221         src = kmap_atomic_prot(s, prot);
 222         if (!src)
 223                 return -ENOMEM;
 224
 225         memcpy_toio(dst, src, PAGE_SIZE);
 226
 227         kunmap_atomic(src);
 228
 229         return 0;
 230 }
 231
 232 int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
 233                        struct ttm_operation_ctx *ctx,
 234                        struct ttm_resource *new_mem)
 235 {
 236         struct ttm_bo_device *bdev = bo->bdev;
 237         struct ttm_resource_manager *man = ttm_manager_type(bdev, new_mem->mem_type);
 238         struct ttm_tt *ttm = bo->ttm;
 239         struct ttm_resource *old_mem = &bo->mem;
 240         struct ttm_resource old_copy = *old_mem;
 241         void *old_iomap;
 242         void *new_iomap;
 243         int ret;
 244         unsigned long i;
 245         unsigned long page;
 246         unsigned long add = 0;
 247         int dir;
 248
 249         ret = ttm_bo_wait_ctx(bo, ctx);
 250         if (ret)
 251                 return ret;
 252
 253         ret = ttm_resource_ioremap(bdev, old_mem, &old_iomap);
 254         if (ret)
 255                 return ret;
 256         ret = ttm_resource_ioremap(bdev, new_mem, &new_iomap);
 257         if (ret)
 258                 goto out;
 259
 260         /*
 261          * Single TTM move. NOP.
 262          */
 263         if (old_iomap == NULL && new_iomap == NULL)
 264                 goto out2;
 265
 266         /*
 267          * Don't move nonexistent data. Clear destination instead.
 268          */
 269         if (old_iomap == NULL &&
 270             (ttm == NULL || (!ttm_tt_is_populated(ttm) &&
 271                              !(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)))) {
 272                 memset_io(new_iomap, 0, new_mem->num_pages*PAGE_SIZE);
 273                 goto out2;
 274         }
 275
 276         /*
 277          * TTM might be null for moves within the same region.
 278          */
 279         if (ttm) {
 280                 ret = ttm_tt_populate(bdev, ttm, ctx);
 281                 if (ret)
 282                         goto out1;
 283         }
 284
 285         add = 0;
 286         dir = 1;
 287
 288         if ((old_mem->mem_type == new_mem->mem_type) &&
 289             (new_mem->start < old_mem->start + old_mem->size)) {
 290                 dir = -1;
 291                 add = new_mem->num_pages - 1;
 292         }
 293
 294         for (i = 0; i < new_mem->num_pages; ++i) {
 295                 page = i * dir + add;
 296                 if (old_iomap == NULL) {
 297                         pgprot_t prot = ttm_io_prot(bo, old_mem, PAGE_KERNEL);
 298                         ret = ttm_copy_ttm_io_page(ttm, new_iomap, page,
 299                                                    prot);
 300                 } else if (new_iomap == NULL) {
 301                         pgprot_t prot = ttm_io_prot(bo, new_mem, PAGE_KERNEL);
 302                         ret = ttm_copy_io_ttm_page(ttm, old_iomap, page,
 303                                                    prot);
 304                 } else {
 305                         ret = ttm_copy_io_page(new_iomap, old_iomap, page);
 306                 }
 307                 if (ret)
 308                         goto out1;
 309         }
 310         mb();
 311 out2:
 312         old_copy = *old_mem;
 313
 314         ttm_bo_assign_mem(bo, new_mem);
 315
 316         if (!man->use_tt)
 317                 ttm_bo_tt_destroy(bo);
 318
 319 out1:
 320         ttm_resource_iounmap(bdev, old_mem, new_iomap);
 321 out:
 322         ttm_resource_iounmap(bdev, &old_copy, old_iomap);
 323
 324         /*
 325          * On error, keep the mm node!
 326          */
 327         if (!ret)
 328                 ttm_resource_free(bo, &old_copy);
 329         return ret;
 330 }
 331 EXPORT_SYMBOL(ttm_bo_move_memcpy);
 332
 333 static void ttm_transfered_destroy(struct ttm_buffer_object *bo)
 334 {
 335         struct ttm_transfer_obj *fbo;
 336
 337         fbo = container_of(bo, struct ttm_transfer_obj, base);
 338         ttm_bo_put(fbo->bo);
 339         kfree(fbo);
 340 }
 341
 342 /**
 343  * ttm_buffer_object_transfer
 344  *
 345  * @bo: A pointer to a struct ttm_buffer_object.
 346  * @new_obj: A pointer to a pointer to a newly created ttm_buffer_object,
 347  * holding the data of @bo with the old placement.
 348  *
 349  * This is a utility function that may be called after an accelerated move
 350  * has been scheduled. A new buffer object is created as a placeholder for
 351  * the old data while it's being copied. When that buffer object is idle,
 352  * it can be destroyed, releasing the space of the old placement.
 353  * Returns:
 354  * !0: Failure.
 355  */
 356
 357 static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 358                                       struct ttm_buffer_object **new_obj)
 359 {
 360         struct ttm_transfer_obj *fbo;
 361         int ret;
 362
 363         fbo = kmalloc(sizeof(*fbo), GFP_KERNEL);
 364         if (!fbo)
 365                 return -ENOMEM;
 366
 367         fbo->base = *bo;
 368
 369         ttm_bo_get(bo);
 370         fbo->bo = bo;
 371
 372         /**
 373          * Fix up members that we shouldn't copy directly:
 374          * TODO: Explicit member copy would probably be better here.
 375          */
 376
 377         atomic_inc(&ttm_bo_glob.bo_count);
 378         INIT_LIST_HEAD(&fbo->base.ddestroy);
 379         INIT_LIST_HEAD(&fbo->base.lru);
 380         INIT_LIST_HEAD(&fbo->base.swap);
 381         fbo->base.moving = NULL;
 382         drm_vma_node_reset(&fbo->base.base.vma_node);
 383
 384         kref_init(&fbo->base.kref);
 385         fbo->base.destroy = &ttm_transfered_destroy;
 386         fbo->base.acc_size = 0;
 387         fbo->base.pin_count = 1;
 388         if (bo->type != ttm_bo_type_sg)
 389                 fbo->base.base.resv = &fbo->base.base._resv;
 390
 391         dma_resv_init(&fbo->base.base._resv);
 392         fbo->base.base.dev = NULL;
 393         ret = dma_resv_trylock(&fbo->base.base._resv);
 394         WARN_ON(!ret);
 395
 396         *new_obj = &fbo->base;
 397         return 0;
 398 }
 399
 400 pgprot_t ttm_io_prot(struct ttm_buffer_object *bo, struct ttm_resource *res,
 401                      pgprot_t tmp)
 402 {
 403         struct ttm_resource_manager *man;
 404         enum ttm_caching caching;
 405
 406         man = ttm_manager_type(bo->bdev, res->mem_type);
 407         caching = man->use_tt ? bo->ttm->caching : res->bus.caching;
 408
 409         /* Cached mappings need no adjustment */
 410         if (caching == ttm_cached)
 411                 return tmp;
 412
 413 #if defined(__i386__) || defined(__x86_64__)
 414         if (caching == ttm_write_combined)
 415                 tmp = pgprot_writecombine(tmp);
 416         else if (boot_cpu_data.x86 > 3)
 417                 tmp = pgprot_noncached(tmp);
 418 #endif
 419 #if defined(__ia64__) || defined(__arm__) || defined(__aarch64__) || \
 420     defined(__powerpc__) || defined(__mips__)
 421         if (caching == ttm_write_combined)
 422                 tmp = pgprot_writecombine(tmp);
 423         else
 424                 tmp = pgprot_noncached(tmp);
 425 #endif
 426 #if defined(__sparc__)
 427         tmp = pgprot_noncached(tmp);
 428 #endif
 429         return tmp;
 430 }
 431 EXPORT_SYMBOL(ttm_io_prot);
 432
 433 static int ttm_bo_ioremap(struct ttm_buffer_object *bo,
 434                           unsigned long offset,
 435                           unsigned long size,
 436                           struct ttm_bo_kmap_obj *map)
 437 {
 438         struct ttm_resource *mem = &bo->mem;
 439
 440         if (bo->mem.bus.addr) {
 441                 map->bo_kmap_type = ttm_bo_map_premapped;
 442                 map->virtual = (void *)(((u8 *)bo->mem.bus.addr) + offset);
 443         } else {
 444                 map->bo_kmap_type = ttm_bo_map_iomap;
 445                 if (mem->bus.caching == ttm_write_combined)
 446                         map->virtual = ioremap_wc(bo->mem.bus.offset + offset,
 447                                                   size);
 448                 else
 449                         map->virtual = ioremap(bo->mem.bus.offset + offset,
 450                                                size);
 451         }
 452         return (!map->virtual) ? -ENOMEM : 0;
 453 }
 454
 455 static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
 456                            unsigned long start_page,
 457                            unsigned long num_pages,
 458                            struct ttm_bo_kmap_obj *map)
 459 {
 460         struct ttm_resource *mem = &bo->mem;
 461         struct ttm_operation_ctx ctx = {
 462                 .interruptible = false,
 463                 .no_wait_gpu = false
 464         };
 465         struct ttm_tt *ttm = bo->ttm;
 466         pgprot_t prot;
 467         int ret;
 468
 469         BUG_ON(!ttm);
 470
 471         ret = ttm_tt_populate(bo->bdev, ttm, &ctx);
 472         if (ret)
 473                 return ret;
 474
 475         if (num_pages == 1 && ttm->caching == ttm_cached) {
 476                 /*
 477                  * We're mapping a single page, and the desired
 478                  * page protection is consistent with the bo.
 479                  */
 480
 481                 map->bo_kmap_type = ttm_bo_map_kmap;
 482                 map->page = ttm->pages[start_page];
 483                 map->virtual = kmap(map->page);
 484         } else {
 485                 /*
 486                  * We need to use vmap to get the desired page protection
 487                  * or to make the buffer object look contiguous.
 488                  */
 489                 prot = ttm_io_prot(bo, mem, PAGE_KERNEL);
 490                 map->bo_kmap_type = ttm_bo_map_vmap;
 491                 map->virtual = vmap(ttm->pages + start_page, num_pages,
 492                                     0, prot);
 493         }
 494         return (!map->virtual) ? -ENOMEM : 0;
 495 }
 496
 497 int ttm_bo_kmap(struct ttm_buffer_object *bo,
 498                 unsigned long start_page, unsigned long num_pages,
 499                 struct ttm_bo_kmap_obj *map)
 500 {
 501         unsigned long offset, size;
 502         int ret;
 503
 504         map->virtual = NULL;
 505         map->bo = bo;
 506         if (num_pages > bo->num_pages)
 507                 return -EINVAL;
 508         if (start_page > bo->num_pages)
 509                 return -EINVAL;
 510
 511         ret = ttm_mem_io_reserve(bo->bdev, &bo->mem);
 512         if (ret)
 513                 return ret;
 514         if (!bo->mem.bus.is_iomem) {
 515                 return ttm_bo_kmap_ttm(bo, start_page, num_pages, map);
 516         } else {
 517                 offset = start_page << PAGE_SHIFT;
 518                 size = num_pages << PAGE_SHIFT;
 519                 return ttm_bo_ioremap(bo, offset, size, map);
 520         }
 521 }
 522 EXPORT_SYMBOL(ttm_bo_kmap);
 523
 524 void ttm_bo_kunmap(struct ttm_bo_kmap_obj *map)
 525 {
 526         if (!map->virtual)
 527                 return;
 528         switch (map->bo_kmap_type) {
 529         case ttm_bo_map_iomap:
 530                 iounmap(map->virtual);
 531                 break;
 532         case ttm_bo_map_vmap:
 533                 vunmap(map->virtual);
 534                 break;
 535         case ttm_bo_map_kmap:
 536                 kunmap(map->page);
 537                 break;
 538         case ttm_bo_map_premapped:
 539                 break;
 540         default:
 541                 BUG();
 542         }
 543         ttm_mem_io_free(map->bo->bdev, &map->bo->mem);
 544         map->virtual = NULL;
 545         map->page = NULL;
 546 }
 547 EXPORT_SYMBOL(ttm_bo_kunmap);
 548
 549 static int ttm_bo_wait_free_node(struct ttm_buffer_object *bo,
 550                                  bool dst_use_tt)
 551 {
 552         int ret;
 553         ret = ttm_bo_wait(bo, false, false);
 554         if (ret)
 555                 return ret;
 556
 557         if (!dst_use_tt)
 558                 ttm_bo_tt_destroy(bo);
 559         ttm_resource_free(bo, &bo->mem);
 560         return 0;
 561 }
 562
 563 static int ttm_bo_move_to_ghost(struct ttm_buffer_object *bo,
 564                                 struct dma_fence *fence,
 565                                 bool dst_use_tt)
 566 {
 567         struct ttm_buffer_object *ghost_obj;
 568         int ret;
 569
 570         /**
 571          * This should help pipeline ordinary buffer moves.
 572          *
 573          * Hang old buffer memory on a new buffer object,
 574          * and leave it to be released when the GPU
 575          * operation has completed.
 576          */
 577
 578         dma_fence_put(bo->moving);
 579         bo->moving = dma_fence_get(fence);
 580
 581         ret = ttm_buffer_object_transfer(bo, &ghost_obj);
 582         if (ret)
 583                 return ret;
 584
 585         dma_resv_add_excl_fence(&ghost_obj->base._resv, fence);
 586
 587         /**
 588          * If we're not moving to fixed memory, the TTM object
 589          * needs to stay alive. Otherwhise hang it on the ghost
 590          * bo to be unbound and destroyed.
 591          */
 592
 593         if (dst_use_tt)
 594                 ghost_obj->ttm = NULL;
 595         else
 596                 bo->ttm = NULL;
 597
 598         dma_resv_unlock(&ghost_obj->base._resv);
 599         ttm_bo_put(ghost_obj);
 600         return 0;
 601 }
 602
 603 static void ttm_bo_move_pipeline_evict(struct ttm_buffer_object *bo,
 604                                        struct dma_fence *fence)
 605 {
 606         struct ttm_bo_device *bdev = bo->bdev;
 607         struct ttm_resource_manager *from = ttm_manager_type(bdev, bo->mem.mem_type);
 608
 609         /**
 610          * BO doesn't have a TTM we need to bind/unbind. Just remember
 611          * this eviction and free up the allocation
 612          */
 613         spin_lock(&from->move_lock);
 614         if (!from->move || dma_fence_is_later(fence, from->move)) {
 615                 dma_fence_put(from->move);
 616                 from->move = dma_fence_get(fence);
 617         }
 618         spin_unlock(&from->move_lock);
 619
 620         ttm_resource_free(bo, &bo->mem);
 621
 622         dma_fence_put(bo->moving);
 623         bo->moving = dma_fence_get(fence);
 624 }
 625
 626 int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
 627                               struct dma_fence *fence,
 628                               bool evict,
 629                               bool pipeline,
 630                               struct ttm_resource *new_mem)
 631 {
 632         struct ttm_bo_device *bdev = bo->bdev;
 633         struct ttm_resource_manager *from = ttm_manager_type(bdev, bo->mem.mem_type);
 634         struct ttm_resource_manager *man = ttm_manager_type(bdev, new_mem->mem_type);
 635         int ret = 0;
 636
 637         dma_resv_add_excl_fence(bo->base.resv, fence);
 638         if (!evict)
 639                 ret = ttm_bo_move_to_ghost(bo, fence, man->use_tt);
 640         else if (!from->use_tt && pipeline)
 641                 ttm_bo_move_pipeline_evict(bo, fence);
 642         else
 643                 ret = ttm_bo_wait_free_node(bo, man->use_tt);
 644
 645         if (ret)
 646                 return ret;
 647
 648         ttm_bo_assign_mem(bo, new_mem);
 649
 650         return 0;
 651 }
 652 EXPORT_SYMBOL(ttm_bo_move_accel_cleanup);
 653
 654 int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo)
 655 {
 656         struct ttm_buffer_object *ghost;
 657         int ret;
 658
 659         ret = ttm_buffer_object_transfer(bo, &ghost);
 660         if (ret)
 661                 return ret;
 662
 663         ret = dma_resv_copy_fences(&ghost->base._resv, bo->base.resv);
 664         /* Last resort, wait for the BO to be idle when we are OOM */
 665         if (ret)
 666                 ttm_bo_wait(bo, false, false);
 667
 668         memset(&bo->mem, 0, sizeof(bo->mem));
 669         bo->mem.mem_type = TTM_PL_SYSTEM;
 670         bo->ttm = NULL;
 671
 672         dma_resv_unlock(&ghost->base._resv);
 673         ttm_bo_put(ghost);
 674
 675         return 0;
 676 }