kernel/dma/direct.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2018-2020 Christoph Hellwig.
   4  *
   5  * DMA operations that map physical memory directly without using an IOMMU.
   6  */
   7 #include <linux/memblock.h> /* for max_pfn */
   8 #include <linux/export.h>
   9 #include <linux/mm.h>
  10 #include <linux/dma-map-ops.h>
  11 #include <linux/scatterlist.h>
  12 #include <linux/pfn.h>
  13 #include <linux/vmalloc.h>
  14 #include <linux/set_memory.h>
  15 #include <linux/slab.h>
  16 #include "direct.h"
  17
  18 /*
  19  * Most architectures use ZONE_DMA for the first 16 Megabytes, but some use
  20  * it for entirely different regions. In that case the arch code needs to
  21  * override the variable below for dma-direct to work properly.
  22  */
  23 unsigned int zone_dma_bits __ro_after_init = 24;
  24
  25 static inline dma_addr_t phys_to_dma_direct(struct device *dev,
  26                 phys_addr_t phys)
  27 {
  28         if (force_dma_unencrypted(dev))
  29                 return phys_to_dma_unencrypted(dev, phys);
  30         return phys_to_dma(dev, phys);
  31 }
  32
  33 static inline struct page *dma_direct_to_page(struct device *dev,
  34                 dma_addr_t dma_addr)
  35 {
  36         return pfn_to_page(PHYS_PFN(dma_to_phys(dev, dma_addr)));
  37 }
  38
  39 u64 dma_direct_get_required_mask(struct device *dev)
  40 {
  41         phys_addr_t phys = (phys_addr_t)(max_pfn - 1) << PAGE_SHIFT;
  42         u64 max_dma = phys_to_dma_direct(dev, phys);
  43
  44         return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
  45 }
  46
  47 static gfp_t dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
  48                                   u64 *phys_limit)
  49 {
  50         u64 dma_limit = min_not_zero(dma_mask, dev->bus_dma_limit);
  51
  52         /*
  53          * Optimistically try the zone that the physical address mask falls
  54          * into first.  If that returns memory that isn't actually addressable
  55          * we will fallback to the next lower zone and try again.
  56          *
  57          * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding
  58          * zones.
  59          */
  60         *phys_limit = dma_to_phys(dev, dma_limit);
  61         if (*phys_limit <= DMA_BIT_MASK(zone_dma_bits))
  62                 return GFP_DMA;
  63         if (*phys_limit <= DMA_BIT_MASK(32))
  64                 return GFP_DMA32;
  65         return 0;
  66 }
  67
  68 static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
  69 {
  70         dma_addr_t dma_addr = phys_to_dma_direct(dev, phys);
  71
  72         if (dma_addr == DMA_MAPPING_ERROR)
  73                 return false;
  74         return dma_addr + size - 1 <=
  75                 min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit);
  76 }
  77
  78 static int dma_set_decrypted(struct device *dev, void *vaddr, size_t size)
  79 {
  80         if (!force_dma_unencrypted(dev))
  81                 return 0;
  82         return set_memory_decrypted((unsigned long)vaddr, PFN_UP(size));
  83 }
  84
  85 static int dma_set_encrypted(struct device *dev, void *vaddr, size_t size)
  86 {
  87         int ret;
  88
  89         if (!force_dma_unencrypted(dev))
  90                 return 0;
  91         ret = set_memory_encrypted((unsigned long)vaddr, PFN_UP(size));
  92         if (ret)
  93                 pr_warn_ratelimited("leaking DMA memory that can't be re-encrypted\n");
  94         return ret;
  95 }
  96
  97 static void __dma_direct_free_pages(struct device *dev, struct page *page,
  98                                     size_t size)
  99 {
 100         if (swiotlb_free(dev, page, size))
 101                 return;
 102         dma_free_contiguous(dev, page, size);
 103 }
 104
 105 static struct page *dma_direct_alloc_swiotlb(struct device *dev, size_t size)
 106 {
 107         struct page *page = swiotlb_alloc(dev, size);
 108
 109         if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
 110                 swiotlb_free(dev, page, size);
 111                 return NULL;
 112         }
 113
 114         return page;
 115 }
 116
 117 static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
 118                 gfp_t gfp, bool allow_highmem)
 119 {
 120         int node = dev_to_node(dev);
 121         struct page *page = NULL;
 122         u64 phys_limit;
 123
 124         WARN_ON_ONCE(!PAGE_ALIGNED(size));
 125
 126         if (is_swiotlb_for_alloc(dev))
 127                 return dma_direct_alloc_swiotlb(dev, size);
 128
 129         gfp |= dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
 130                                            &phys_limit);
 131         page = dma_alloc_contiguous(dev, size, gfp);
 132         if (page) {
 133                 if (!dma_coherent_ok(dev, page_to_phys(page), size) ||
 134                     (!allow_highmem && PageHighMem(page))) {
 135                         dma_free_contiguous(dev, page, size);
 136                         page = NULL;
 137                 }
 138         }
 139 again:
 140         if (!page)
 141                 page = alloc_pages_node(node, gfp, get_order(size));
 142         if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
 143                 dma_free_contiguous(dev, page, size);
 144                 page = NULL;
 145
 146                 if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
 147                     phys_limit < DMA_BIT_MASK(64) &&
 148                     !(gfp & (GFP_DMA32 | GFP_DMA))) {
 149                         gfp |= GFP_DMA32;
 150                         goto again;
 151                 }
 152
 153                 if (IS_ENABLED(CONFIG_ZONE_DMA) && !(gfp & GFP_DMA)) {
 154                         gfp = (gfp & ~GFP_DMA32) | GFP_DMA;
 155                         goto again;
 156                 }
 157         }
 158
 159         return page;
 160 }
 161
 162 /*
 163  * Check if a potentially blocking operations needs to dip into the atomic
 164  * pools for the given device/gfp.
 165  */
 166 static bool dma_direct_use_pool(struct device *dev, gfp_t gfp)
 167 {
 168         return !gfpflags_allow_blocking(gfp) && !is_swiotlb_for_alloc(dev);
 169 }
 170
 171 static void *dma_direct_alloc_from_pool(struct device *dev, size_t size,
 172                 dma_addr_t *dma_handle, gfp_t gfp)
 173 {
 174         struct page *page;
 175         u64 phys_mask;
 176         void *ret;
 177
 178         if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_DMA_COHERENT_POOL)))
 179                 return NULL;
 180
 181         gfp |= dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
 182                                            &phys_mask);
 183         page = dma_alloc_from_pool(dev, size, &ret, gfp, dma_coherent_ok);
 184         if (!page)
 185                 return NULL;
 186         *dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
 187         return ret;
 188 }
 189
 190 static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size,
 191                 dma_addr_t *dma_handle, gfp_t gfp)
 192 {
 193         struct page *page;
 194
 195         page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
 196         if (!page)
 197                 return NULL;
 198
 199         /* remove any dirty cache lines on the kernel alias */
 200         if (!PageHighMem(page))
 201                 arch_dma_prep_coherent(page, size);
 202
 203         /* return the page pointer as the opaque cookie */
 204         *dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
 205         return page;
 206 }
 207
 208 void *dma_direct_alloc(struct device *dev, size_t size,
 209                 dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
 210 {
 211         bool remap = false, set_uncached = false;
 212         struct page *page;
 213         void *ret;
 214
 215         size = PAGE_ALIGN(size);
 216         if (attrs & DMA_ATTR_NO_WARN)
 217                 gfp |= __GFP_NOWARN;
 218
 219         if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
 220             !force_dma_unencrypted(dev) && !is_swiotlb_for_alloc(dev))
 221                 return dma_direct_alloc_no_mapping(dev, size, dma_handle, gfp);
 222
 223         if (!dev_is_dma_coherent(dev)) {
 224                 /*
 225                  * Fallback to the arch handler if it exists.  This should
 226                  * eventually go away.
 227                  */
 228                 if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
 229                     !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
 230                     !IS_ENABLED(CONFIG_DMA_GLOBAL_POOL) &&
 231                     !is_swiotlb_for_alloc(dev))
 232                         return arch_dma_alloc(dev, size, dma_handle, gfp,
 233                                               attrs);
 234
 235                 /*
 236                  * If there is a global pool, always allocate from it for
 237                  * non-coherent devices.
 238                  */
 239                 if (IS_ENABLED(CONFIG_DMA_GLOBAL_POOL))
 240                         return dma_alloc_from_global_coherent(dev, size,
 241                                         dma_handle);
 242
 243                 /*
 244                  * Otherwise remap if the architecture is asking for it.  But
 245                  * given that remapping memory is a blocking operation we'll
 246                  * instead have to dip into the atomic pools.
 247                  */
 248                 remap = IS_ENABLED(CONFIG_DMA_DIRECT_REMAP);
 249                 if (remap) {
 250                         if (dma_direct_use_pool(dev, gfp))
 251                                 return dma_direct_alloc_from_pool(dev, size,
 252                                                 dma_handle, gfp);
 253                 } else {
 254                         if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED))
 255                                 return NULL;
 256                         set_uncached = true;
 257                 }
 258         }
 259
 260         /*
 261          * Decrypting memory may block, so allocate the memory from the atomic
 262          * pools if we can't block.
 263          */
 264         if (force_dma_unencrypted(dev) && dma_direct_use_pool(dev, gfp))
 265                 return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
 266
 267         /* we always manually zero the memory once we are done */
 268         page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
 269         if (!page)
 270                 return NULL;
 271
 272         /*
 273          * dma_alloc_contiguous can return highmem pages depending on a
 274          * combination the cma= arguments and per-arch setup.  These need to be
 275          * remapped to return a kernel virtual address.
 276          */
 277         if (PageHighMem(page)) {
 278                 remap = true;
 279                 set_uncached = false;
 280         }
 281
 282         if (remap) {
 283                 pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
 284
 285                 if (force_dma_unencrypted(dev))
 286                         prot = pgprot_decrypted(prot);
 287
 288                 /* remove any dirty cache lines on the kernel alias */
 289                 arch_dma_prep_coherent(page, size);
 290
 291                 /* create a coherent mapping */
 292                 ret = dma_common_contiguous_remap(page, size, prot,
 293                                 __builtin_return_address(0));
 294                 if (!ret)
 295                         goto out_free_pages;
 296         } else {
 297                 ret = page_address(page);
 298                 if (dma_set_decrypted(dev, ret, size))
 299                         goto out_free_pages;
 300         }
 301
 302         memset(ret, 0, size);
 303
 304         if (set_uncached) {
 305                 arch_dma_prep_coherent(page, size);
 306                 ret = arch_dma_set_uncached(ret, size);
 307                 if (IS_ERR(ret))
 308                         goto out_encrypt_pages;
 309         }
 310
 311         *dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
 312         return ret;
 313
 314 out_encrypt_pages:
 315         if (dma_set_encrypted(dev, page_address(page), size))
 316                 return NULL;
 317 out_free_pages:
 318         __dma_direct_free_pages(dev, page, size);
 319         return NULL;
 320 }
 321
 322 void dma_direct_free(struct device *dev, size_t size,
 323                 void *cpu_addr, dma_addr_t dma_addr, unsigned long attrs)
 324 {
 325         unsigned int page_order = get_order(size);
 326
 327         if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
 328             !force_dma_unencrypted(dev) && !is_swiotlb_for_alloc(dev)) {
 329                 /* cpu_addr is a struct page cookie, not a kernel address */
 330                 dma_free_contiguous(dev, cpu_addr, size);
 331                 return;
 332         }
 333
 334         if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
 335             !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
 336             !IS_ENABLED(CONFIG_DMA_GLOBAL_POOL) &&
 337             !dev_is_dma_coherent(dev) &&
 338             !is_swiotlb_for_alloc(dev)) {
 339                 arch_dma_free(dev, size, cpu_addr, dma_addr, attrs);
 340                 return;
 341         }
 342
 343         if (IS_ENABLED(CONFIG_DMA_GLOBAL_POOL) &&
 344             !dev_is_dma_coherent(dev)) {
 345                 if (!dma_release_from_global_coherent(page_order, cpu_addr))
 346                         WARN_ON_ONCE(1);
 347                 return;
 348         }
 349
 350         /* If cpu_addr is not from an atomic pool, dma_free_from_pool() fails */
 351         if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
 352             dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
 353                 return;
 354
 355         if (is_vmalloc_addr(cpu_addr)) {
 356                 vunmap(cpu_addr);
 357         } else {
 358                 if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
 359                         arch_dma_clear_uncached(cpu_addr, size);
 360                 if (dma_set_encrypted(dev, cpu_addr, size))
 361                         return;
 362         }
 363
 364         __dma_direct_free_pages(dev, dma_direct_to_page(dev, dma_addr), size);
 365 }
 366
 367 struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
 368                 dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp)
 369 {
 370         struct page *page;
 371         void *ret;
 372
 373         if (force_dma_unencrypted(dev) && dma_direct_use_pool(dev, gfp))
 374                 return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
 375
 376         page = __dma_direct_alloc_pages(dev, size, gfp, false);
 377         if (!page)
 378                 return NULL;
 379
 380         ret = page_address(page);
 381         if (dma_set_decrypted(dev, ret, size))
 382                 goto out_free_pages;
 383         memset(ret, 0, size);
 384         *dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
 385         return page;
 386 out_free_pages:
 387         __dma_direct_free_pages(dev, page, size);
 388         return NULL;
 389 }
 390
 391 void dma_direct_free_pages(struct device *dev, size_t size,
 392                 struct page *page, dma_addr_t dma_addr,
 393                 enum dma_data_direction dir)
 394 {
 395         void *vaddr = page_address(page);
 396
 397         /* If cpu_addr is not from an atomic pool, dma_free_from_pool() fails */
 398         if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
 399             dma_free_from_pool(dev, vaddr, size))
 400                 return;
 401
 402         if (dma_set_encrypted(dev, vaddr, size))
 403                 return;
 404         __dma_direct_free_pages(dev, page, size);
 405 }
 406
 407 #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
 408     defined(CONFIG_SWIOTLB)
 409 void dma_direct_sync_sg_for_device(struct device *dev,
 410                 struct scatterlist *sgl, int nents, enum dma_data_direction dir)
 411 {
 412         struct scatterlist *sg;
 413         int i;
 414
 415         for_each_sg(sgl, sg, nents, i) {
 416                 phys_addr_t paddr = dma_to_phys(dev, sg_dma_address(sg));
 417
 418                 if (unlikely(is_swiotlb_buffer(dev, paddr)))
 419                         swiotlb_sync_single_for_device(dev, paddr, sg->length,
 420                                                        dir);
 421
 422                 if (!dev_is_dma_coherent(dev))
 423                         arch_sync_dma_for_device(paddr, sg->length,
 424                                         dir);
 425         }
 426 }
 427 #endif
 428
 429 #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \
 430     defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL) || \
 431     defined(CONFIG_SWIOTLB)
 432 void dma_direct_sync_sg_for_cpu(struct device *dev,
 433                 struct scatterlist *sgl, int nents, enum dma_data_direction dir)
 434 {
 435         struct scatterlist *sg;
 436         int i;
 437
 438         for_each_sg(sgl, sg, nents, i) {
 439                 phys_addr_t paddr = dma_to_phys(dev, sg_dma_address(sg));
 440
 441                 if (!dev_is_dma_coherent(dev))
 442                         arch_sync_dma_for_cpu(paddr, sg->length, dir);
 443
 444                 if (unlikely(is_swiotlb_buffer(dev, paddr)))
 445                         swiotlb_sync_single_for_cpu(dev, paddr, sg->length,
 446                                                     dir);
 447
 448                 if (dir == DMA_FROM_DEVICE)
 449                         arch_dma_mark_clean(paddr, sg->length);
 450         }
 451
 452         if (!dev_is_dma_coherent(dev))
 453                 arch_sync_dma_for_cpu_all();
 454 }
 455
 456 void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sgl,
 457                 int nents, enum dma_data_direction dir, unsigned long attrs)
 458 {
 459         struct scatterlist *sg;
 460         int i;
 461
 462         for_each_sg(sgl, sg, nents, i)
 463                 dma_direct_unmap_page(dev, sg->dma_address, sg_dma_len(sg), dir,
 464                              attrs);
 465 }
 466 #endif
 467
 468 int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
 469                 enum dma_data_direction dir, unsigned long attrs)
 470 {
 471         int i;
 472         struct scatterlist *sg;
 473
 474         for_each_sg(sgl, sg, nents, i) {
 475                 sg->dma_address = dma_direct_map_page(dev, sg_page(sg),
 476                                 sg->offset, sg->length, dir, attrs);
 477                 if (sg->dma_address == DMA_MAPPING_ERROR)
 478                         goto out_unmap;
 479                 sg_dma_len(sg) = sg->length;
 480         }
 481
 482         return nents;
 483
 484 out_unmap:
 485         dma_direct_unmap_sg(dev, sgl, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
 486         return -EIO;
 487 }
 488
 489 dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
 490                 size_t size, enum dma_data_direction dir, unsigned long attrs)
 491 {
 492         dma_addr_t dma_addr = paddr;
 493
 494         if (unlikely(!dma_capable(dev, dma_addr, size, false))) {
 495                 dev_err_once(dev,
 496                              "DMA addr %pad+%zu overflow (mask %llx, bus limit %llx).\n",
 497                              &dma_addr, size, *dev->dma_mask, dev->bus_dma_limit);
 498                 WARN_ON_ONCE(1);
 499                 return DMA_MAPPING_ERROR;
 500         }
 501
 502         return dma_addr;
 503 }
 504
 505 int dma_direct_get_sgtable(struct device *dev, struct sg_table *sgt,
 506                 void *cpu_addr, dma_addr_t dma_addr, size_t size,
 507                 unsigned long attrs)
 508 {
 509         struct page *page = dma_direct_to_page(dev, dma_addr);
 510         int ret;
 511
 512         ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
 513         if (!ret)
 514                 sg_set_page(sgt->sgl, page, PAGE_ALIGN(size), 0);
 515         return ret;
 516 }
 517
 518 bool dma_direct_can_mmap(struct device *dev)
 519 {
 520         return dev_is_dma_coherent(dev) ||
 521                 IS_ENABLED(CONFIG_DMA_NONCOHERENT_MMAP);
 522 }
 523
 524 int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
 525                 void *cpu_addr, dma_addr_t dma_addr, size_t size,
 526                 unsigned long attrs)
 527 {
 528         unsigned long user_count = vma_pages(vma);
 529         unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
 530         unsigned long pfn = PHYS_PFN(dma_to_phys(dev, dma_addr));
 531         int ret = -ENXIO;
 532
 533         vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, attrs);
 534         if (force_dma_unencrypted(dev))
 535                 vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 536
 537         if (dma_mmap_from_dev_coherent(dev, vma, cpu_addr, size, &ret))
 538                 return ret;
 539         if (dma_mmap_from_global_coherent(vma, cpu_addr, size, &ret))
 540                 return ret;
 541
 542         if (vma->vm_pgoff >= count || user_count > count - vma->vm_pgoff)
 543                 return -ENXIO;
 544         return remap_pfn_range(vma, vma->vm_start, pfn + vma->vm_pgoff,
 545                         user_count << PAGE_SHIFT, vma->vm_page_prot);
 546 }
 547
 548 int dma_direct_supported(struct device *dev, u64 mask)
 549 {
 550         u64 min_mask = (max_pfn - 1) << PAGE_SHIFT;
 551
 552         /*
 553          * Because 32-bit DMA masks are so common we expect every architecture
 554          * to be able to satisfy them - either by not supporting more physical
 555          * memory, or by providing a ZONE_DMA32.  If neither is the case, the
 556          * architecture needs to use an IOMMU instead of the direct mapping.
 557          */
 558         if (mask >= DMA_BIT_MASK(32))
 559                 return 1;
 560
 561         /*
 562          * This check needs to be against the actual bit mask value, so use
 563          * phys_to_dma_unencrypted() here so that the SME encryption mask isn't
 564          * part of the check.
 565          */
 566         if (IS_ENABLED(CONFIG_ZONE_DMA))
 567                 min_mask = min_t(u64, min_mask, DMA_BIT_MASK(zone_dma_bits));
 568         return mask >= phys_to_dma_unencrypted(dev, min_mask);
 569 }
 570
 571 size_t dma_direct_max_mapping_size(struct device *dev)
 572 {
 573         /* If SWIOTLB is active, use its maximum mapping size */
 574         if (is_swiotlb_active(dev) &&
 575             (dma_addressing_limited(dev) || is_swiotlb_force_bounce(dev)))
 576                 return swiotlb_max_mapping_size(dev);
 577         return SIZE_MAX;
 578 }
 579
 580 bool dma_direct_need_sync(struct device *dev, dma_addr_t dma_addr)
 581 {
 582         return !dev_is_dma_coherent(dev) ||
 583                is_swiotlb_buffer(dev, dma_to_phys(dev, dma_addr));
 584 }
 585
 586 /**
 587  * dma_direct_set_offset - Assign scalar offset for a single DMA range.
 588  * @dev:        device pointer; needed to "own" the alloced memory.
 589  * @cpu_start:  beginning of memory region covered by this offset.
 590  * @dma_start:  beginning of DMA/PCI region covered by this offset.
 591  * @size:       size of the region.
 592  *
 593  * This is for the simple case of a uniform offset which cannot
 594  * be discovered by "dma-ranges".
 595  *
 596  * It returns -ENOMEM if out of memory, -EINVAL if a map
 597  * already exists, 0 otherwise.
 598  *
 599  * Note: any call to this from a driver is a bug.  The mapping needs
 600  * to be described by the device tree or other firmware interfaces.
 601  */
 602 int dma_direct_set_offset(struct device *dev, phys_addr_t cpu_start,
 603                          dma_addr_t dma_start, u64 size)
 604 {
 605         struct bus_dma_region *map;
 606         u64 offset = (u64)cpu_start - (u64)dma_start;
 607
 608         if (dev->dma_range_map) {
 609                 dev_err(dev, "attempt to add DMA range to existing map\n");
 610                 return -EINVAL;
 611         }
 612
 613         if (!offset)
 614                 return 0;
 615
 616         map = kcalloc(2, sizeof(*map), GFP_KERNEL);
 617         if (!map)
 618                 return -ENOMEM;
 619         map[0].cpu_start = cpu_start;
 620         map[0].dma_start = dma_start;
 621         map[0].offset = offset;
 622         map[0].size = size;
 623         dev->dma_range_map = map;
 624         return 0;
 625 }