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_cache.h>
  35 #include <drm/drm_vma_manager.h>
  36 #include <linux/dma-buf-map.h>
  37 #include <linux/io.h>
  38 #include <linux/highmem.h>
  39 #include <linux/wait.h>
  40 #include <linux/slab.h>
  41 #include <linux/vmalloc.h>
  42 #include <linux/module.h>
  43 #include <linux/dma-resv.h>
  44
  45 struct ttm_transfer_obj {
  46         struct ttm_buffer_object base;
  47         struct ttm_buffer_object *bo;
  48 };
  49
  50 int ttm_mem_io_reserve(struct ttm_device *bdev,
  51                        struct ttm_resource *mem)
  52 {
  53         if (mem->bus.offset || mem->bus.addr)
  54                 return 0;
  55
  56         mem->bus.is_iomem = false;
  57         if (!bdev->funcs->io_mem_reserve)
  58                 return 0;
  59
  60         return bdev->funcs->io_mem_reserve(bdev, mem);
  61 }
  62
  63 void ttm_mem_io_free(struct ttm_device *bdev,
  64                      struct ttm_resource *mem)
  65 {
  66         if (!mem)
  67                 return;
  68
  69         if (!mem->bus.offset && !mem->bus.addr)
  70                 return;
  71
  72         if (bdev->funcs->io_mem_free)
  73                 bdev->funcs->io_mem_free(bdev, mem);
  74
  75         mem->bus.offset = 0;
  76         mem->bus.addr = NULL;
  77 }
  78
  79 /**
  80  * ttm_move_memcpy - Helper to perform a memcpy ttm move operation.
  81  * @bo: The struct ttm_buffer_object.
  82  * @new_mem: The struct ttm_resource we're moving to (copy destination).
  83  * @new_iter: A struct ttm_kmap_iter representing the destination resource.
  84  * @src_iter: A struct ttm_kmap_iter representing the source resource.
  85  *
  86  * This function is intended to be able to move out async under a
  87  * dma-fence if desired.
  88  */
  89 void ttm_move_memcpy(struct ttm_buffer_object *bo,
  90                      u32 num_pages,
  91                      struct ttm_kmap_iter *dst_iter,
  92                      struct ttm_kmap_iter *src_iter)
  93 {
  94         const struct ttm_kmap_iter_ops *dst_ops = dst_iter->ops;
  95         const struct ttm_kmap_iter_ops *src_ops = src_iter->ops;
  96         struct ttm_tt *ttm = bo->ttm;
  97         struct dma_buf_map src_map, dst_map;
  98         pgoff_t i;
  99
 100         /* Single TTM move. NOP */
 101         if (dst_ops->maps_tt && src_ops->maps_tt)
 102                 return;
 103
 104         /* Don't move nonexistent data. Clear destination instead. */
 105         if (src_ops->maps_tt && (!ttm || !ttm_tt_is_populated(ttm))) {
 106                 if (ttm && !(ttm->page_flags & TTM_PAGE_FLAG_ZERO_ALLOC))
 107                         return;
 108
 109                 for (i = 0; i < num_pages; ++i) {
 110                         dst_ops->map_local(dst_iter, &dst_map, i);
 111                         if (dst_map.is_iomem)
 112                                 memset_io(dst_map.vaddr_iomem, 0, PAGE_SIZE);
 113                         else
 114                                 memset(dst_map.vaddr, 0, PAGE_SIZE);
 115                         if (dst_ops->unmap_local)
 116                                 dst_ops->unmap_local(dst_iter, &dst_map);
 117                 }
 118                 return;
 119         }
 120
 121         for (i = 0; i < num_pages; ++i) {
 122                 dst_ops->map_local(dst_iter, &dst_map, i);
 123                 src_ops->map_local(src_iter, &src_map, i);
 124
 125                 drm_memcpy_from_wc(&dst_map, &src_map, PAGE_SIZE);
 126
 127                 if (src_ops->unmap_local)
 128                         src_ops->unmap_local(src_iter, &src_map);
 129                 if (dst_ops->unmap_local)
 130                         dst_ops->unmap_local(dst_iter, &dst_map);
 131         }
 132 }
 133 EXPORT_SYMBOL(ttm_move_memcpy);
 134
 135 int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
 136                        struct ttm_operation_ctx *ctx,
 137                        struct ttm_resource *dst_mem)
 138 {
 139         struct ttm_device *bdev = bo->bdev;
 140         struct ttm_resource_manager *dst_man =
 141                 ttm_manager_type(bo->bdev, dst_mem->mem_type);
 142         struct ttm_tt *ttm = bo->ttm;
 143         struct ttm_resource *src_mem = bo->resource;
 144         struct ttm_resource_manager *src_man =
 145                 ttm_manager_type(bdev, src_mem->mem_type);
 146         union {
 147                 struct ttm_kmap_iter_tt tt;
 148                 struct ttm_kmap_iter_linear_io io;
 149         } _dst_iter, _src_iter;
 150         struct ttm_kmap_iter *dst_iter, *src_iter;
 151         int ret = 0;
 152
 153         if (ttm && ((ttm->page_flags & TTM_PAGE_FLAG_SWAPPED) ||
 154                     dst_man->use_tt)) {
 155                 ret = ttm_tt_populate(bdev, ttm, ctx);
 156                 if (ret)
 157                         return ret;
 158         }
 159
 160         dst_iter = ttm_kmap_iter_linear_io_init(&_dst_iter.io, bdev, dst_mem);
 161         if (PTR_ERR(dst_iter) == -EINVAL && dst_man->use_tt)
 162                 dst_iter = ttm_kmap_iter_tt_init(&_dst_iter.tt, bo->ttm);
 163         if (IS_ERR(dst_iter))
 164                 return PTR_ERR(dst_iter);
 165
 166         src_iter = ttm_kmap_iter_linear_io_init(&_src_iter.io, bdev, src_mem);
 167         if (PTR_ERR(src_iter) == -EINVAL && src_man->use_tt)
 168                 src_iter = ttm_kmap_iter_tt_init(&_src_iter.tt, bo->ttm);
 169         if (IS_ERR(src_iter)) {
 170                 ret = PTR_ERR(src_iter);
 171                 goto out_src_iter;
 172         }
 173
 174         ttm_move_memcpy(bo, dst_mem->num_pages, dst_iter, src_iter);
 175
 176         if (!src_iter->ops->maps_tt)
 177                 ttm_kmap_iter_linear_io_fini(&_src_iter.io, bdev, src_mem);
 178         ttm_bo_move_sync_cleanup(bo, dst_mem);
 179
 180 out_src_iter:
 181         if (!dst_iter->ops->maps_tt)
 182                 ttm_kmap_iter_linear_io_fini(&_dst_iter.io, bdev, dst_mem);
 183
 184         return ret;
 185 }
 186 EXPORT_SYMBOL(ttm_bo_move_memcpy);
 187
 188 static void ttm_transfered_destroy(struct ttm_buffer_object *bo)
 189 {
 190         struct ttm_transfer_obj *fbo;
 191
 192         fbo = container_of(bo, struct ttm_transfer_obj, base);
 193         ttm_bo_put(fbo->bo);
 194         kfree(fbo);
 195 }
 196
 197 /**
 198  * ttm_buffer_object_transfer
 199  *
 200  * @bo: A pointer to a struct ttm_buffer_object.
 201  * @new_obj: A pointer to a pointer to a newly created ttm_buffer_object,
 202  * holding the data of @bo with the old placement.
 203  *
 204  * This is a utility function that may be called after an accelerated move
 205  * has been scheduled. A new buffer object is created as a placeholder for
 206  * the old data while it's being copied. When that buffer object is idle,
 207  * it can be destroyed, releasing the space of the old placement.
 208  * Returns:
 209  * !0: Failure.
 210  */
 211
 212 static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 213                                       struct ttm_buffer_object **new_obj)
 214 {
 215         struct ttm_transfer_obj *fbo;
 216         int ret;
 217
 218         fbo = kmalloc(sizeof(*fbo), GFP_KERNEL);
 219         if (!fbo)
 220                 return -ENOMEM;
 221
 222         fbo->base = *bo;
 223
 224         ttm_bo_get(bo);
 225         fbo->bo = bo;
 226
 227         /**
 228          * Fix up members that we shouldn't copy directly:
 229          * TODO: Explicit member copy would probably be better here.
 230          */
 231
 232         atomic_inc(&ttm_glob.bo_count);
 233         INIT_LIST_HEAD(&fbo->base.ddestroy);
 234         INIT_LIST_HEAD(&fbo->base.lru);
 235         fbo->base.moving = NULL;
 236         drm_vma_node_reset(&fbo->base.base.vma_node);
 237
 238         kref_init(&fbo->base.kref);
 239         fbo->base.destroy = &ttm_transfered_destroy;
 240         fbo->base.pin_count = 0;
 241         if (bo->type != ttm_bo_type_sg)
 242                 fbo->base.base.resv = &fbo->base.base._resv;
 243
 244         dma_resv_init(&fbo->base.base._resv);
 245         fbo->base.base.dev = NULL;
 246         ret = dma_resv_trylock(&fbo->base.base._resv);
 247         WARN_ON(!ret);
 248
 249         ttm_bo_move_to_lru_tail_unlocked(&fbo->base);
 250
 251         *new_obj = &fbo->base;
 252         return 0;
 253 }
 254
 255 pgprot_t ttm_io_prot(struct ttm_buffer_object *bo, struct ttm_resource *res,
 256                      pgprot_t tmp)
 257 {
 258         struct ttm_resource_manager *man;
 259         enum ttm_caching caching;
 260
 261         man = ttm_manager_type(bo->bdev, res->mem_type);
 262         caching = man->use_tt ? bo->ttm->caching : res->bus.caching;
 263
 264         return ttm_prot_from_caching(caching, tmp);
 265 }
 266 EXPORT_SYMBOL(ttm_io_prot);
 267
 268 static int ttm_bo_ioremap(struct ttm_buffer_object *bo,
 269                           unsigned long offset,
 270                           unsigned long size,
 271                           struct ttm_bo_kmap_obj *map)
 272 {
 273         struct ttm_resource *mem = bo->resource;
 274
 275         if (bo->resource->bus.addr) {
 276                 map->bo_kmap_type = ttm_bo_map_premapped;
 277                 map->virtual = ((u8 *)bo->resource->bus.addr) + offset;
 278         } else {
 279                 resource_size_t res = bo->resource->bus.offset + offset;
 280
 281                 map->bo_kmap_type = ttm_bo_map_iomap;
 282                 if (mem->bus.caching == ttm_write_combined)
 283                         map->virtual = ioremap_wc(res, size);
 284 #ifdef CONFIG_X86
 285                 else if (mem->bus.caching == ttm_cached)
 286                         map->virtual = ioremap_cache(res, size);
 287 #endif
 288                 else
 289                         map->virtual = ioremap(res, size);
 290         }
 291         return (!map->virtual) ? -ENOMEM : 0;
 292 }
 293
 294 static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
 295                            unsigned long start_page,
 296                            unsigned long num_pages,
 297                            struct ttm_bo_kmap_obj *map)
 298 {
 299         struct ttm_resource *mem = bo->resource;
 300         struct ttm_operation_ctx ctx = {
 301                 .interruptible = false,
 302                 .no_wait_gpu = false
 303         };
 304         struct ttm_tt *ttm = bo->ttm;
 305         pgprot_t prot;
 306         int ret;
 307
 308         BUG_ON(!ttm);
 309
 310         ret = ttm_tt_populate(bo->bdev, ttm, &ctx);
 311         if (ret)
 312                 return ret;
 313
 314         if (num_pages == 1 && ttm->caching == ttm_cached) {
 315                 /*
 316                  * We're mapping a single page, and the desired
 317                  * page protection is consistent with the bo.
 318                  */
 319
 320                 map->bo_kmap_type = ttm_bo_map_kmap;
 321                 map->page = ttm->pages[start_page];
 322                 map->virtual = kmap(map->page);
 323         } else {
 324                 /*
 325                  * We need to use vmap to get the desired page protection
 326                  * or to make the buffer object look contiguous.
 327                  */
 328                 prot = ttm_io_prot(bo, mem, PAGE_KERNEL);
 329                 map->bo_kmap_type = ttm_bo_map_vmap;
 330                 map->virtual = vmap(ttm->pages + start_page, num_pages,
 331                                     0, prot);
 332         }
 333         return (!map->virtual) ? -ENOMEM : 0;
 334 }
 335
 336 int ttm_bo_kmap(struct ttm_buffer_object *bo,
 337                 unsigned long start_page, unsigned long num_pages,
 338                 struct ttm_bo_kmap_obj *map)
 339 {
 340         unsigned long offset, size;
 341         int ret;
 342
 343         map->virtual = NULL;
 344         map->bo = bo;
 345         if (num_pages > bo->resource->num_pages)
 346                 return -EINVAL;
 347         if ((start_page + num_pages) > bo->resource->num_pages)
 348                 return -EINVAL;
 349
 350         ret = ttm_mem_io_reserve(bo->bdev, bo->resource);
 351         if (ret)
 352                 return ret;
 353         if (!bo->resource->bus.is_iomem) {
 354                 return ttm_bo_kmap_ttm(bo, start_page, num_pages, map);
 355         } else {
 356                 offset = start_page << PAGE_SHIFT;
 357                 size = num_pages << PAGE_SHIFT;
 358                 return ttm_bo_ioremap(bo, offset, size, map);
 359         }
 360 }
 361 EXPORT_SYMBOL(ttm_bo_kmap);
 362
 363 void ttm_bo_kunmap(struct ttm_bo_kmap_obj *map)
 364 {
 365         if (!map->virtual)
 366                 return;
 367         switch (map->bo_kmap_type) {
 368         case ttm_bo_map_iomap:
 369                 iounmap(map->virtual);
 370                 break;
 371         case ttm_bo_map_vmap:
 372                 vunmap(map->virtual);
 373                 break;
 374         case ttm_bo_map_kmap:
 375                 kunmap(map->page);
 376                 break;
 377         case ttm_bo_map_premapped:
 378                 break;
 379         default:
 380                 BUG();
 381         }
 382         ttm_mem_io_free(map->bo->bdev, map->bo->resource);
 383         map->virtual = NULL;
 384         map->page = NULL;
 385 }
 386 EXPORT_SYMBOL(ttm_bo_kunmap);
 387
 388 int ttm_bo_vmap(struct ttm_buffer_object *bo, struct dma_buf_map *map)
 389 {
 390         struct ttm_resource *mem = bo->resource;
 391         int ret;
 392
 393         ret = ttm_mem_io_reserve(bo->bdev, mem);
 394         if (ret)
 395                 return ret;
 396
 397         if (mem->bus.is_iomem) {
 398                 void __iomem *vaddr_iomem;
 399
 400                 if (mem->bus.addr)
 401                         vaddr_iomem = (void __iomem *)mem->bus.addr;
 402                 else if (mem->bus.caching == ttm_write_combined)
 403                         vaddr_iomem = ioremap_wc(mem->bus.offset,
 404                                                  bo->base.size);
 405 #ifdef CONFIG_X86
 406                 else if (mem->bus.caching == ttm_cached)
 407                         vaddr_iomem = ioremap_cache(mem->bus.offset,
 408                                                   bo->base.size);
 409 #endif
 410                 else
 411                         vaddr_iomem = ioremap(mem->bus.offset, bo->base.size);
 412
 413                 if (!vaddr_iomem)
 414                         return -ENOMEM;
 415
 416                 dma_buf_map_set_vaddr_iomem(map, vaddr_iomem);
 417
 418         } else {
 419                 struct ttm_operation_ctx ctx = {
 420                         .interruptible = false,
 421                         .no_wait_gpu = false
 422                 };
 423                 struct ttm_tt *ttm = bo->ttm;
 424                 pgprot_t prot;
 425                 void *vaddr;
 426
 427                 ret = ttm_tt_populate(bo->bdev, ttm, &ctx);
 428                 if (ret)
 429                         return ret;
 430
 431                 /*
 432                  * We need to use vmap to get the desired page protection
 433                  * or to make the buffer object look contiguous.
 434                  */
 435                 prot = ttm_io_prot(bo, mem, PAGE_KERNEL);
 436                 vaddr = vmap(ttm->pages, ttm->num_pages, 0, prot);
 437                 if (!vaddr)
 438                         return -ENOMEM;
 439
 440                 dma_buf_map_set_vaddr(map, vaddr);
 441         }
 442
 443         return 0;
 444 }
 445 EXPORT_SYMBOL(ttm_bo_vmap);
 446
 447 void ttm_bo_vunmap(struct ttm_buffer_object *bo, struct dma_buf_map *map)
 448 {
 449         struct ttm_resource *mem = bo->resource;
 450
 451         if (dma_buf_map_is_null(map))
 452                 return;
 453
 454         if (!map->is_iomem)
 455                 vunmap(map->vaddr);
 456         else if (!mem->bus.addr)
 457                 iounmap(map->vaddr_iomem);
 458         dma_buf_map_clear(map);
 459
 460         ttm_mem_io_free(bo->bdev, bo->resource);
 461 }
 462 EXPORT_SYMBOL(ttm_bo_vunmap);
 463
 464 static int ttm_bo_wait_free_node(struct ttm_buffer_object *bo,
 465                                  bool dst_use_tt)
 466 {
 467         int ret;
 468         ret = ttm_bo_wait(bo, false, false);
 469         if (ret)
 470                 return ret;
 471
 472         if (!dst_use_tt)
 473                 ttm_bo_tt_destroy(bo);
 474         ttm_resource_free(bo, &bo->resource);
 475         return 0;
 476 }
 477
 478 static int ttm_bo_move_to_ghost(struct ttm_buffer_object *bo,
 479                                 struct dma_fence *fence,
 480                                 bool dst_use_tt)
 481 {
 482         struct ttm_buffer_object *ghost_obj;
 483         int ret;
 484
 485         /**
 486          * This should help pipeline ordinary buffer moves.
 487          *
 488          * Hang old buffer memory on a new buffer object,
 489          * and leave it to be released when the GPU
 490          * operation has completed.
 491          */
 492
 493         dma_fence_put(bo->moving);
 494         bo->moving = dma_fence_get(fence);
 495
 496         ret = ttm_buffer_object_transfer(bo, &ghost_obj);
 497         if (ret)
 498                 return ret;
 499
 500         dma_resv_add_excl_fence(&ghost_obj->base._resv, fence);
 501
 502         /**
 503          * If we're not moving to fixed memory, the TTM object
 504          * needs to stay alive. Otherwhise hang it on the ghost
 505          * bo to be unbound and destroyed.
 506          */
 507
 508         if (dst_use_tt)
 509                 ghost_obj->ttm = NULL;
 510         else
 511                 bo->ttm = NULL;
 512         bo->resource = NULL;
 513
 514         dma_resv_unlock(&ghost_obj->base._resv);
 515         ttm_bo_put(ghost_obj);
 516         return 0;
 517 }
 518
 519 static void ttm_bo_move_pipeline_evict(struct ttm_buffer_object *bo,
 520                                        struct dma_fence *fence)
 521 {
 522         struct ttm_device *bdev = bo->bdev;
 523         struct ttm_resource_manager *from;
 524
 525         from = ttm_manager_type(bdev, bo->resource->mem_type);
 526
 527         /**
 528          * BO doesn't have a TTM we need to bind/unbind. Just remember
 529          * this eviction and free up the allocation
 530          */
 531         spin_lock(&from->move_lock);
 532         if (!from->move || dma_fence_is_later(fence, from->move)) {
 533                 dma_fence_put(from->move);
 534                 from->move = dma_fence_get(fence);
 535         }
 536         spin_unlock(&from->move_lock);
 537
 538         ttm_resource_free(bo, &bo->resource);
 539
 540         dma_fence_put(bo->moving);
 541         bo->moving = dma_fence_get(fence);
 542 }
 543
 544 int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
 545                               struct dma_fence *fence,
 546                               bool evict,
 547                               bool pipeline,
 548                               struct ttm_resource *new_mem)
 549 {
 550         struct ttm_device *bdev = bo->bdev;
 551         struct ttm_resource_manager *from = ttm_manager_type(bdev, bo->resource->mem_type);
 552         struct ttm_resource_manager *man = ttm_manager_type(bdev, new_mem->mem_type);
 553         int ret = 0;
 554
 555         dma_resv_add_excl_fence(bo->base.resv, fence);
 556         if (!evict)
 557                 ret = ttm_bo_move_to_ghost(bo, fence, man->use_tt);
 558         else if (!from->use_tt && pipeline)
 559                 ttm_bo_move_pipeline_evict(bo, fence);
 560         else
 561                 ret = ttm_bo_wait_free_node(bo, man->use_tt);
 562
 563         if (ret)
 564                 return ret;
 565
 566         ttm_bo_assign_mem(bo, new_mem);
 567
 568         return 0;
 569 }
 570 EXPORT_SYMBOL(ttm_bo_move_accel_cleanup);
 571
 572 /**
 573  * ttm_bo_pipeline_gutting - purge the contents of a bo
 574  * @bo: The buffer object
 575  *
 576  * Purge the contents of a bo, async if the bo is not idle.
 577  * After a successful call, the bo is left unpopulated in
 578  * system placement. The function may wait uninterruptible
 579  * for idle on OOM.
 580  *
 581  * Return: 0 if successful, negative error code on failure.
 582  */
 583 int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo)
 584 {
 585         static const struct ttm_place sys_mem = { .mem_type = TTM_PL_SYSTEM };
 586         struct ttm_buffer_object *ghost;
 587         struct ttm_resource *sys_res;
 588         struct ttm_tt *ttm;
 589         int ret;
 590
 591         ret = ttm_resource_alloc(bo, &sys_mem, &sys_res);
 592         if (ret)
 593                 return ret;
 594
 595         /* If already idle, no need for ghost object dance. */
 596         ret = ttm_bo_wait(bo, false, true);
 597         if (ret != -EBUSY) {
 598                 if (!bo->ttm) {
 599                         /* See comment below about clearing. */
 600                         ret = ttm_tt_create(bo, true);
 601                         if (ret)
 602                                 goto error_free_sys_mem;
 603                 } else {
 604                         ttm_tt_unpopulate(bo->bdev, bo->ttm);
 605                         if (bo->type == ttm_bo_type_device)
 606                                 ttm_tt_mark_for_clear(bo->ttm);
 607                 }
 608                 ttm_resource_free(bo, &bo->resource);
 609                 ttm_bo_assign_mem(bo, sys_res);
 610                 return 0;
 611         }
 612
 613         /*
 614          * We need an unpopulated ttm_tt after giving our current one,
 615          * if any, to the ghost object. And we can't afford to fail
 616          * creating one *after* the operation. If the bo subsequently gets
 617          * resurrected, make sure it's cleared (if ttm_bo_type_device)
 618          * to avoid leaking sensitive information to user-space.
 619          */
 620
 621         ttm = bo->ttm;
 622         bo->ttm = NULL;
 623         ret = ttm_tt_create(bo, true);
 624         swap(bo->ttm, ttm);
 625         if (ret)
 626                 goto error_free_sys_mem;
 627
 628         ret = ttm_buffer_object_transfer(bo, &ghost);
 629         if (ret)
 630                 goto error_destroy_tt;
 631
 632         ret = dma_resv_copy_fences(&ghost->base._resv, bo->base.resv);
 633         /* Last resort, wait for the BO to be idle when we are OOM */
 634         if (ret)
 635                 ttm_bo_wait(bo, false, false);
 636
 637         dma_resv_unlock(&ghost->base._resv);
 638         ttm_bo_put(ghost);
 639         bo->ttm = ttm;
 640         bo->resource = NULL;
 641         ttm_bo_assign_mem(bo, sys_res);
 642         return 0;
 643
 644 error_destroy_tt:
 645         ttm_tt_destroy(bo->bdev, ttm);
 646
 647 error_free_sys_mem:
 648         ttm_resource_free(bo, &sys_res);
 649         return ret;
 650 }