drivers/gpu/drm/i915/gem/i915_gem_pages.c

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright © 2014-2016 Intel Corporation
   5  */
   6
   7 #include <drm/drm_cache.h>
   8
   9 #include "i915_drv.h"
  10 #include "i915_gem_object.h"
  11 #include "i915_scatterlist.h"
  12 #include "i915_gem_lmem.h"
  13 #include "i915_gem_mman.h"
  14
  15 #include "gt/intel_gt.h"
  16
  17 void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
  18                                  struct sg_table *pages,
  19                                  unsigned int sg_page_sizes)
  20 {
  21         struct drm_i915_private *i915 = to_i915(obj->base.dev);
  22         unsigned long supported = INTEL_INFO(i915)->page_sizes;
  23         bool shrinkable;
  24         int i;
  25
  26         assert_object_held_shared(obj);
  27
  28         if (i915_gem_object_is_volatile(obj))
  29                 obj->mm.madv = I915_MADV_DONTNEED;
  30
  31         /* Make the pages coherent with the GPU (flushing any swapin). */
  32         if (obj->cache_dirty) {
  33                 WARN_ON_ONCE(IS_DGFX(i915));
  34                 obj->write_domain = 0;
  35                 if (i915_gem_object_has_struct_page(obj))
  36                         drm_clflush_sg(pages);
  37                 obj->cache_dirty = false;
  38         }
  39
  40         obj->mm.get_page.sg_pos = pages->sgl;
  41         obj->mm.get_page.sg_idx = 0;
  42         obj->mm.get_dma_page.sg_pos = pages->sgl;
  43         obj->mm.get_dma_page.sg_idx = 0;
  44
  45         obj->mm.pages = pages;
  46
  47         GEM_BUG_ON(!sg_page_sizes);
  48         obj->mm.page_sizes.phys = sg_page_sizes;
  49
  50         /*
  51          * Calculate the supported page-sizes which fit into the given
  52          * sg_page_sizes. This will give us the page-sizes which we may be able
  53          * to use opportunistically when later inserting into the GTT. For
  54          * example if phys=2G, then in theory we should be able to use 1G, 2M,
  55          * 64K or 4K pages, although in practice this will depend on a number of
  56          * other factors.
  57          */
  58         obj->mm.page_sizes.sg = 0;
  59         for_each_set_bit(i, &supported, ilog2(I915_GTT_MAX_PAGE_SIZE) + 1) {
  60                 if (obj->mm.page_sizes.phys & ~0u << i)
  61                         obj->mm.page_sizes.sg |= BIT(i);
  62         }
  63         GEM_BUG_ON(!HAS_PAGE_SIZES(i915, obj->mm.page_sizes.sg));
  64
  65         shrinkable = i915_gem_object_is_shrinkable(obj);
  66
  67         if (i915_gem_object_is_tiled(obj) &&
  68             i915->quirks & QUIRK_PIN_SWIZZLED_PAGES) {
  69                 GEM_BUG_ON(i915_gem_object_has_tiling_quirk(obj));
  70                 i915_gem_object_set_tiling_quirk(obj);
  71                 GEM_BUG_ON(!list_empty(&obj->mm.link));
  72                 atomic_inc(&obj->mm.shrink_pin);
  73                 shrinkable = false;
  74         }
  75
  76         if (shrinkable && !i915_gem_object_has_self_managed_shrink_list(obj)) {
  77                 struct list_head *list;
  78                 unsigned long flags;
  79
  80                 assert_object_held(obj);
  81                 spin_lock_irqsave(&i915->mm.obj_lock, flags);
  82
  83                 i915->mm.shrink_count++;
  84                 i915->mm.shrink_memory += obj->base.size;
  85
  86                 if (obj->mm.madv != I915_MADV_WILLNEED)
  87                         list = &i915->mm.purge_list;
  88                 else
  89                         list = &i915->mm.shrink_list;
  90                 list_add_tail(&obj->mm.link, list);
  91
  92                 atomic_set(&obj->mm.shrink_pin, 0);
  93                 spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
  94         }
  95 }
  96
  97 int ____i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
  98 {
  99         struct drm_i915_private *i915 = to_i915(obj->base.dev);
 100         int err;
 101
 102         assert_object_held_shared(obj);
 103
 104         if (unlikely(obj->mm.madv != I915_MADV_WILLNEED)) {
 105                 drm_dbg(&i915->drm,
 106                         "Attempting to obtain a purgeable object\n");
 107                 return -EFAULT;
 108         }
 109
 110         err = obj->ops->get_pages(obj);
 111         GEM_BUG_ON(!err && !i915_gem_object_has_pages(obj));
 112
 113         return err;
 114 }
 115
 116 /* Ensure that the associated pages are gathered from the backing storage
 117  * and pinned into our object. i915_gem_object_pin_pages() may be called
 118  * multiple times before they are released by a single call to
 119  * i915_gem_object_unpin_pages() - once the pages are no longer referenced
 120  * either as a result of memory pressure (reaping pages under the shrinker)
 121  * or as the object is itself released.
 122  */
 123 int __i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
 124 {
 125         int err;
 126
 127         assert_object_held(obj);
 128
 129         assert_object_held_shared(obj);
 130
 131         if (unlikely(!i915_gem_object_has_pages(obj))) {
 132                 GEM_BUG_ON(i915_gem_object_has_pinned_pages(obj));
 133
 134                 err = ____i915_gem_object_get_pages(obj);
 135                 if (err)
 136                         return err;
 137
 138                 smp_mb__before_atomic();
 139         }
 140         atomic_inc(&obj->mm.pages_pin_count);
 141
 142         return 0;
 143 }
 144
 145 int i915_gem_object_pin_pages_unlocked(struct drm_i915_gem_object *obj)
 146 {
 147         struct i915_gem_ww_ctx ww;
 148         int err;
 149
 150         i915_gem_ww_ctx_init(&ww, true);
 151 retry:
 152         err = i915_gem_object_lock(obj, &ww);
 153         if (!err)
 154                 err = i915_gem_object_pin_pages(obj);
 155
 156         if (err == -EDEADLK) {
 157                 err = i915_gem_ww_ctx_backoff(&ww);
 158                 if (!err)
 159                         goto retry;
 160         }
 161         i915_gem_ww_ctx_fini(&ww);
 162         return err;
 163 }
 164
 165 /* Immediately discard the backing storage */
 166 int i915_gem_object_truncate(struct drm_i915_gem_object *obj)
 167 {
 168         if (obj->ops->truncate)
 169                 return obj->ops->truncate(obj);
 170
 171         return 0;
 172 }
 173
 174 static void __i915_gem_object_reset_page_iter(struct drm_i915_gem_object *obj)
 175 {
 176         struct radix_tree_iter iter;
 177         void __rcu **slot;
 178
 179         rcu_read_lock();
 180         radix_tree_for_each_slot(slot, &obj->mm.get_page.radix, &iter, 0)
 181                 radix_tree_delete(&obj->mm.get_page.radix, iter.index);
 182         radix_tree_for_each_slot(slot, &obj->mm.get_dma_page.radix, &iter, 0)
 183                 radix_tree_delete(&obj->mm.get_dma_page.radix, iter.index);
 184         rcu_read_unlock();
 185 }
 186
 187 static void unmap_object(struct drm_i915_gem_object *obj, void *ptr)
 188 {
 189         if (is_vmalloc_addr(ptr))
 190                 vunmap(ptr);
 191 }
 192
 193 struct sg_table *
 194 __i915_gem_object_unset_pages(struct drm_i915_gem_object *obj)
 195 {
 196         struct sg_table *pages;
 197
 198         assert_object_held_shared(obj);
 199
 200         pages = fetch_and_zero(&obj->mm.pages);
 201         if (IS_ERR_OR_NULL(pages))
 202                 return pages;
 203
 204         if (i915_gem_object_is_volatile(obj))
 205                 obj->mm.madv = I915_MADV_WILLNEED;
 206
 207         if (!i915_gem_object_has_self_managed_shrink_list(obj))
 208                 i915_gem_object_make_unshrinkable(obj);
 209
 210         if (obj->mm.mapping) {
 211                 unmap_object(obj, page_mask_bits(obj->mm.mapping));
 212                 obj->mm.mapping = NULL;
 213         }
 214
 215         __i915_gem_object_reset_page_iter(obj);
 216         obj->mm.page_sizes.phys = obj->mm.page_sizes.sg = 0;
 217
 218         if (test_and_clear_bit(I915_BO_WAS_BOUND_BIT, &obj->flags)) {
 219                 struct drm_i915_private *i915 = to_i915(obj->base.dev);
 220                 intel_wakeref_t wakeref;
 221
 222                 with_intel_runtime_pm_if_active(&i915->runtime_pm, wakeref)
 223                         intel_gt_invalidate_tlbs(to_gt(i915));
 224         }
 225
 226         return pages;
 227 }
 228
 229 int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
 230 {
 231         struct sg_table *pages;
 232
 233         if (i915_gem_object_has_pinned_pages(obj))
 234                 return -EBUSY;
 235
 236         /* May be called by shrinker from within get_pages() (on another bo) */
 237         assert_object_held_shared(obj);
 238
 239         i915_gem_object_release_mmap_offset(obj);
 240
 241         /*
 242          * ->put_pages might need to allocate memory for the bit17 swizzle
 243          * array, hence protect them from being reaped by removing them from gtt
 244          * lists early.
 245          */
 246         pages = __i915_gem_object_unset_pages(obj);
 247
 248         /*
 249          * XXX Temporary hijinx to avoid updating all backends to handle
 250          * NULL pages. In the future, when we have more asynchronous
 251          * get_pages backends we should be better able to handle the
 252          * cancellation of the async task in a more uniform manner.
 253          */
 254         if (!IS_ERR_OR_NULL(pages))
 255                 obj->ops->put_pages(obj, pages);
 256
 257         return 0;
 258 }
 259
 260 /* The 'mapping' part of i915_gem_object_pin_map() below */
 261 static void *i915_gem_object_map_page(struct drm_i915_gem_object *obj,
 262                                       enum i915_map_type type)
 263 {
 264         unsigned long n_pages = obj->base.size >> PAGE_SHIFT, i;
 265         struct page *stack[32], **pages = stack, *page;
 266         struct sgt_iter iter;
 267         pgprot_t pgprot;
 268         void *vaddr;
 269
 270         switch (type) {
 271         default:
 272                 MISSING_CASE(type);
 273                 fallthrough;    /* to use PAGE_KERNEL anyway */
 274         case I915_MAP_WB:
 275                 /*
 276                  * On 32b, highmem using a finite set of indirect PTE (i.e.
 277                  * vmap) to provide virtual mappings of the high pages.
 278                  * As these are finite, map_new_virtual() must wait for some
 279                  * other kmap() to finish when it runs out. If we map a large
 280                  * number of objects, there is no method for it to tell us
 281                  * to release the mappings, and we deadlock.
 282                  *
 283                  * However, if we make an explicit vmap of the page, that
 284                  * uses a larger vmalloc arena, and also has the ability
 285                  * to tell us to release unwanted mappings. Most importantly,
 286                  * it will fail and propagate an error instead of waiting
 287                  * forever.
 288                  *
 289                  * So if the page is beyond the 32b boundary, make an explicit
 290                  * vmap.
 291                  */
 292                 if (n_pages == 1 && !PageHighMem(sg_page(obj->mm.pages->sgl)))
 293                         return page_address(sg_page(obj->mm.pages->sgl));
 294                 pgprot = PAGE_KERNEL;
 295                 break;
 296         case I915_MAP_WC:
 297                 pgprot = pgprot_writecombine(PAGE_KERNEL_IO);
 298                 break;
 299         }
 300
 301         if (n_pages > ARRAY_SIZE(stack)) {
 302                 /* Too big for stack -- allocate temporary array instead */
 303                 pages = kvmalloc_array(n_pages, sizeof(*pages), GFP_KERNEL);
 304                 if (!pages)
 305                         return ERR_PTR(-ENOMEM);
 306         }
 307
 308         i = 0;
 309         for_each_sgt_page(page, iter, obj->mm.pages)
 310                 pages[i++] = page;
 311         vaddr = vmap(pages, n_pages, 0, pgprot);
 312         if (pages != stack)
 313                 kvfree(pages);
 314
 315         return vaddr ?: ERR_PTR(-ENOMEM);
 316 }
 317
 318 static void *i915_gem_object_map_pfn(struct drm_i915_gem_object *obj,
 319                                      enum i915_map_type type)
 320 {
 321         resource_size_t iomap = obj->mm.region->iomap.base -
 322                 obj->mm.region->region.start;
 323         unsigned long n_pfn = obj->base.size >> PAGE_SHIFT;
 324         unsigned long stack[32], *pfns = stack, i;
 325         struct sgt_iter iter;
 326         dma_addr_t addr;
 327         void *vaddr;
 328
 329         GEM_BUG_ON(type != I915_MAP_WC);
 330
 331         if (n_pfn > ARRAY_SIZE(stack)) {
 332                 /* Too big for stack -- allocate temporary array instead */
 333                 pfns = kvmalloc_array(n_pfn, sizeof(*pfns), GFP_KERNEL);
 334                 if (!pfns)
 335                         return ERR_PTR(-ENOMEM);
 336         }
 337
 338         i = 0;
 339         for_each_sgt_daddr(addr, iter, obj->mm.pages)
 340                 pfns[i++] = (iomap + addr) >> PAGE_SHIFT;
 341         vaddr = vmap_pfn(pfns, n_pfn, pgprot_writecombine(PAGE_KERNEL_IO));
 342         if (pfns != stack)
 343                 kvfree(pfns);
 344
 345         return vaddr ?: ERR_PTR(-ENOMEM);
 346 }
 347
 348 /* get, pin, and map the pages of the object into kernel space */
 349 void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
 350                               enum i915_map_type type)
 351 {
 352         enum i915_map_type has_type;
 353         bool pinned;
 354         void *ptr;
 355         int err;
 356
 357         if (!i915_gem_object_has_struct_page(obj) &&
 358             !i915_gem_object_has_iomem(obj))
 359                 return ERR_PTR(-ENXIO);
 360
 361         if (WARN_ON_ONCE(obj->flags & I915_BO_ALLOC_GPU_ONLY))
 362                 return ERR_PTR(-EINVAL);
 363
 364         assert_object_held(obj);
 365
 366         pinned = !(type & I915_MAP_OVERRIDE);
 367         type &= ~I915_MAP_OVERRIDE;
 368
 369         if (!atomic_inc_not_zero(&obj->mm.pages_pin_count)) {
 370                 if (unlikely(!i915_gem_object_has_pages(obj))) {
 371                         GEM_BUG_ON(i915_gem_object_has_pinned_pages(obj));
 372
 373                         err = ____i915_gem_object_get_pages(obj);
 374                         if (err)
 375                                 return ERR_PTR(err);
 376
 377                         smp_mb__before_atomic();
 378                 }
 379                 atomic_inc(&obj->mm.pages_pin_count);
 380                 pinned = false;
 381         }
 382         GEM_BUG_ON(!i915_gem_object_has_pages(obj));
 383
 384         /*
 385          * For discrete our CPU mappings needs to be consistent in order to
 386          * function correctly on !x86. When mapping things through TTM, we use
 387          * the same rules to determine the caching type.
 388          *
 389          * The caching rules, starting from DG1:
 390          *
 391          *      - If the object can be placed in device local-memory, then the
 392          *        pages should be allocated and mapped as write-combined only.
 393          *
 394          *      - Everything else is always allocated and mapped as write-back,
 395          *        with the guarantee that everything is also coherent with the
 396          *        GPU.
 397          *
 398          * Internal users of lmem are already expected to get this right, so no
 399          * fudging needed there.
 400          */
 401         if (i915_gem_object_placement_possible(obj, INTEL_MEMORY_LOCAL)) {
 402                 if (type != I915_MAP_WC && !obj->mm.n_placements) {
 403                         ptr = ERR_PTR(-ENODEV);
 404                         goto err_unpin;
 405                 }
 406
 407                 type = I915_MAP_WC;
 408         } else if (IS_DGFX(to_i915(obj->base.dev))) {
 409                 type = I915_MAP_WB;
 410         }
 411
 412         ptr = page_unpack_bits(obj->mm.mapping, &has_type);
 413         if (ptr && has_type != type) {
 414                 if (pinned) {
 415                         ptr = ERR_PTR(-EBUSY);
 416                         goto err_unpin;
 417                 }
 418
 419                 unmap_object(obj, ptr);
 420
 421                 ptr = obj->mm.mapping = NULL;
 422         }
 423
 424         if (!ptr) {
 425                 err = i915_gem_object_wait_moving_fence(obj, true);
 426                 if (err) {
 427                         ptr = ERR_PTR(err);
 428                         goto err_unpin;
 429                 }
 430
 431                 if (GEM_WARN_ON(type == I915_MAP_WC && !pat_enabled()))
 432                         ptr = ERR_PTR(-ENODEV);
 433                 else if (i915_gem_object_has_struct_page(obj))
 434                         ptr = i915_gem_object_map_page(obj, type);
 435                 else
 436                         ptr = i915_gem_object_map_pfn(obj, type);
 437                 if (IS_ERR(ptr))
 438                         goto err_unpin;
 439
 440                 obj->mm.mapping = page_pack_bits(ptr, type);
 441         }
 442
 443         return ptr;
 444
 445 err_unpin:
 446         atomic_dec(&obj->mm.pages_pin_count);
 447         return ptr;
 448 }
 449
 450 void *i915_gem_object_pin_map_unlocked(struct drm_i915_gem_object *obj,
 451                                        enum i915_map_type type)
 452 {
 453         void *ret;
 454
 455         i915_gem_object_lock(obj, NULL);
 456         ret = i915_gem_object_pin_map(obj, type);
 457         i915_gem_object_unlock(obj);
 458
 459         return ret;
 460 }
 461
 462 void __i915_gem_object_flush_map(struct drm_i915_gem_object *obj,
 463                                  unsigned long offset,
 464                                  unsigned long size)
 465 {
 466         enum i915_map_type has_type;
 467         void *ptr;
 468
 469         GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
 470         GEM_BUG_ON(range_overflows_t(typeof(obj->base.size),
 471                                      offset, size, obj->base.size));
 472
 473         wmb(); /* let all previous writes be visible to coherent partners */
 474         obj->mm.dirty = true;
 475
 476         if (obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_WRITE)
 477                 return;
 478
 479         ptr = page_unpack_bits(obj->mm.mapping, &has_type);
 480         if (has_type == I915_MAP_WC)
 481                 return;
 482
 483         drm_clflush_virt_range(ptr + offset, size);
 484         if (size == obj->base.size) {
 485                 obj->write_domain &= ~I915_GEM_DOMAIN_CPU;
 486                 obj->cache_dirty = false;
 487         }
 488 }
 489
 490 void __i915_gem_object_release_map(struct drm_i915_gem_object *obj)
 491 {
 492         GEM_BUG_ON(!obj->mm.mapping);
 493
 494         /*
 495          * We allow removing the mapping from underneath pinned pages!
 496          *
 497          * Furthermore, since this is an unsafe operation reserved only
 498          * for construction time manipulation, we ignore locking prudence.
 499          */
 500         unmap_object(obj, page_mask_bits(fetch_and_zero(&obj->mm.mapping)));
 501
 502         i915_gem_object_unpin_map(obj);
 503 }
 504
 505 struct scatterlist *
 506 __i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
 507                          struct i915_gem_object_page_iter *iter,
 508                          unsigned int n,
 509                          unsigned int *offset,
 510                          bool dma)
 511 {
 512         struct scatterlist *sg;
 513         unsigned int idx, count;
 514
 515         might_sleep();
 516         GEM_BUG_ON(n >= obj->base.size >> PAGE_SHIFT);
 517         if (!i915_gem_object_has_pinned_pages(obj))
 518                 assert_object_held(obj);
 519
 520         /* As we iterate forward through the sg, we record each entry in a
 521          * radixtree for quick repeated (backwards) lookups. If we have seen
 522          * this index previously, we will have an entry for it.
 523          *
 524          * Initial lookup is O(N), but this is amortized to O(1) for
 525          * sequential page access (where each new request is consecutive
 526          * to the previous one). Repeated lookups are O(lg(obj->base.size)),
 527          * i.e. O(1) with a large constant!
 528          */
 529         if (n < READ_ONCE(iter->sg_idx))
 530                 goto lookup;
 531
 532         mutex_lock(&iter->lock);
 533
 534         /* We prefer to reuse the last sg so that repeated lookup of this
 535          * (or the subsequent) sg are fast - comparing against the last
 536          * sg is faster than going through the radixtree.
 537          */
 538
 539         sg = iter->sg_pos;
 540         idx = iter->sg_idx;
 541         count = dma ? __sg_dma_page_count(sg) : __sg_page_count(sg);
 542
 543         while (idx + count <= n) {
 544                 void *entry;
 545                 unsigned long i;
 546                 int ret;
 547
 548                 /* If we cannot allocate and insert this entry, or the
 549                  * individual pages from this range, cancel updating the
 550                  * sg_idx so that on this lookup we are forced to linearly
 551                  * scan onwards, but on future lookups we will try the
 552                  * insertion again (in which case we need to be careful of
 553                  * the error return reporting that we have already inserted
 554                  * this index).
 555                  */
 556                 ret = radix_tree_insert(&iter->radix, idx, sg);
 557                 if (ret && ret != -EEXIST)
 558                         goto scan;
 559
 560                 entry = xa_mk_value(idx);
 561                 for (i = 1; i < count; i++) {
 562                         ret = radix_tree_insert(&iter->radix, idx + i, entry);
 563                         if (ret && ret != -EEXIST)
 564                                 goto scan;
 565                 }
 566
 567                 idx += count;
 568                 sg = ____sg_next(sg);
 569                 count = dma ? __sg_dma_page_count(sg) : __sg_page_count(sg);
 570         }
 571
 572 scan:
 573         iter->sg_pos = sg;
 574         iter->sg_idx = idx;
 575
 576         mutex_unlock(&iter->lock);
 577
 578         if (unlikely(n < idx)) /* insertion completed by another thread */
 579                 goto lookup;
 580
 581         /* In case we failed to insert the entry into the radixtree, we need
 582          * to look beyond the current sg.
 583          */
 584         while (idx + count <= n) {
 585                 idx += count;
 586                 sg = ____sg_next(sg);
 587                 count = dma ? __sg_dma_page_count(sg) : __sg_page_count(sg);
 588         }
 589
 590         *offset = n - idx;
 591         return sg;
 592
 593 lookup:
 594         rcu_read_lock();
 595
 596         sg = radix_tree_lookup(&iter->radix, n);
 597         GEM_BUG_ON(!sg);
 598
 599         /* If this index is in the middle of multi-page sg entry,
 600          * the radix tree will contain a value entry that points
 601          * to the start of that range. We will return the pointer to
 602          * the base page and the offset of this page within the
 603          * sg entry's range.
 604          */
 605         *offset = 0;
 606         if (unlikely(xa_is_value(sg))) {
 607                 unsigned long base = xa_to_value(sg);
 608
 609                 sg = radix_tree_lookup(&iter->radix, base);
 610                 GEM_BUG_ON(!sg);
 611
 612                 *offset = n - base;
 613         }
 614
 615         rcu_read_unlock();
 616
 617         return sg;
 618 }
 619
 620 struct page *
 621 i915_gem_object_get_page(struct drm_i915_gem_object *obj, unsigned int n)
 622 {
 623         struct scatterlist *sg;
 624         unsigned int offset;
 625
 626         GEM_BUG_ON(!i915_gem_object_has_struct_page(obj));
 627
 628         sg = i915_gem_object_get_sg(obj, n, &offset);
 629         return nth_page(sg_page(sg), offset);
 630 }
 631
 632 /* Like i915_gem_object_get_page(), but mark the returned page dirty */
 633 struct page *
 634 i915_gem_object_get_dirty_page(struct drm_i915_gem_object *obj,
 635                                unsigned int n)
 636 {
 637         struct page *page;
 638
 639         page = i915_gem_object_get_page(obj, n);
 640         if (!obj->mm.dirty)
 641                 set_page_dirty(page);
 642
 643         return page;
 644 }
 645
 646 dma_addr_t
 647 i915_gem_object_get_dma_address_len(struct drm_i915_gem_object *obj,
 648                                     unsigned long n,
 649                                     unsigned int *len)
 650 {
 651         struct scatterlist *sg;
 652         unsigned int offset;
 653
 654         sg = i915_gem_object_get_sg_dma(obj, n, &offset);
 655
 656         if (len)
 657                 *len = sg_dma_len(sg) - (offset << PAGE_SHIFT);
 658
 659         return sg_dma_address(sg) + (offset << PAGE_SHIFT);
 660 }
 661
 662 dma_addr_t
 663 i915_gem_object_get_dma_address(struct drm_i915_gem_object *obj,
 664                                 unsigned long n)
 665 {
 666         return i915_gem_object_get_dma_address_len(obj, n, NULL);
 667 }