arch/i386/kernel/e820.c

   1 #include <linux/kernel.h>
   2 #include <linux/types.h>
   3 #include <linux/init.h>
   4 #include <linux/bootmem.h>
   5 #include <linux/ioport.h>
   6 #include <linux/string.h>
   7 #include <linux/kexec.h>
   8 #include <linux/module.h>
   9 #include <linux/mm.h>
  10 #include <linux/efi.h>
  11 #include <linux/pfn.h>
  12
  13 #include <asm/pgtable.h>
  14 #include <asm/page.h>
  15 #include <asm/e820.h>
  16
  17 #ifdef CONFIG_EFI
  18 int efi_enabled = 0;
  19 EXPORT_SYMBOL(efi_enabled);
  20 #endif
  21
  22 struct e820map e820;
  23 struct change_member {
  24         struct e820entry *pbios; /* pointer to original bios entry */
  25         unsigned long long addr; /* address for this change point */
  26 };
  27 static struct change_member change_point_list[2*E820MAX] __initdata;
  28 static struct change_member *change_point[2*E820MAX] __initdata;
  29 static struct e820entry *overlap_list[E820MAX] __initdata;
  30 static struct e820entry new_bios[E820MAX] __initdata;
  31 /* For PCI or other memory-mapped resources */
  32 unsigned long pci_mem_start = 0x10000000;
  33 #ifdef CONFIG_PCI
  34 EXPORT_SYMBOL(pci_mem_start);
  35 #endif
  36 struct resource data_resource = {
  37         .name   = "Kernel data",
  38         .start  = 0,
  39         .end    = 0,
  40         .flags  = IORESOURCE_BUSY | IORESOURCE_MEM
  41 };
  42
  43 struct resource code_resource = {
  44         .name   = "Kernel code",
  45         .start  = 0,
  46         .end    = 0,
  47         .flags  = IORESOURCE_BUSY | IORESOURCE_MEM
  48 };
  49
  50 static struct resource system_rom_resource = {
  51         .name   = "System ROM",
  52         .start  = 0xf0000,
  53         .end    = 0xfffff,
  54         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
  55 };
  56
  57 static struct resource extension_rom_resource = {
  58         .name   = "Extension ROM",
  59         .start  = 0xe0000,
  60         .end    = 0xeffff,
  61         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
  62 };
  63
  64 static struct resource adapter_rom_resources[] = { {
  65         .name   = "Adapter ROM",
  66         .start  = 0xc8000,
  67         .end    = 0,
  68         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
  69 }, {
  70         .name   = "Adapter ROM",
  71         .start  = 0,
  72         .end    = 0,
  73         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
  74 }, {
  75         .name   = "Adapter ROM",
  76         .start  = 0,
  77         .end    = 0,
  78         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
  79 }, {
  80         .name   = "Adapter ROM",
  81         .start  = 0,
  82         .end    = 0,
  83         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
  84 }, {
  85         .name   = "Adapter ROM",
  86         .start  = 0,
  87         .end    = 0,
  88         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
  89 }, {
  90         .name   = "Adapter ROM",
  91         .start  = 0,
  92         .end    = 0,
  93         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
  94 } };
  95
  96 static struct resource video_rom_resource = {
  97         .name   = "Video ROM",
  98         .start  = 0xc0000,
  99         .end    = 0xc7fff,
 100         .flags  = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
 101 };
 102
 103 static struct resource video_ram_resource = {
 104         .name   = "Video RAM area",
 105         .start  = 0xa0000,
 106         .end    = 0xbffff,
 107         .flags  = IORESOURCE_BUSY | IORESOURCE_MEM
 108 };
 109
 110 static struct resource standard_io_resources[] = { {
 111         .name   = "dma1",
 112         .start  = 0x0000,
 113         .end    = 0x001f,
 114         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 115 }, {
 116         .name   = "pic1",
 117         .start  = 0x0020,
 118         .end    = 0x0021,
 119         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 120 }, {
 121         .name   = "timer0",
 122         .start  = 0x0040,
 123         .end    = 0x0043,
 124         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 125 }, {
 126         .name   = "timer1",
 127         .start  = 0x0050,
 128         .end    = 0x0053,
 129         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 130 }, {
 131         .name   = "keyboard",
 132         .start  = 0x0060,
 133         .end    = 0x006f,
 134         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 135 }, {
 136         .name   = "dma page reg",
 137         .start  = 0x0080,
 138         .end    = 0x008f,
 139         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 140 }, {
 141         .name   = "pic2",
 142         .start  = 0x00a0,
 143         .end    = 0x00a1,
 144         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 145 }, {
 146         .name   = "dma2",
 147         .start  = 0x00c0,
 148         .end    = 0x00df,
 149         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 150 }, {
 151         .name   = "fpu",
 152         .start  = 0x00f0,
 153         .end    = 0x00ff,
 154         .flags  = IORESOURCE_BUSY | IORESOURCE_IO
 155 } };
 156
 157 #define romsignature(x) (*(unsigned short *)(x) == 0xaa55)
 158
 159 static int __init romchecksum(unsigned char *rom, unsigned long length)
 160 {
 161         unsigned char *p, sum = 0;
 162
 163         for (p = rom; p < rom + length; p++)
 164                 sum += *p;
 165         return sum == 0;
 166 }
 167
 168 static void __init probe_roms(void)
 169 {
 170         unsigned long start, length, upper;
 171         unsigned char *rom;
 172         int           i;
 173
 174         /* video rom */
 175         upper = adapter_rom_resources[0].start;
 176         for (start = video_rom_resource.start; start < upper; start += 2048) {
 177                 rom = isa_bus_to_virt(start);
 178                 if (!romsignature(rom))
 179                         continue;
 180
 181                 video_rom_resource.start = start;
 182
 183                 /* 0 < length <= 0x7f * 512, historically */
 184                 length = rom[2] * 512;
 185
 186                 /* if checksum okay, trust length byte */
 187                 if (length && romchecksum(rom, length))
 188                         video_rom_resource.end = start + length - 1;
 189
 190                 request_resource(&iomem_resource, &video_rom_resource);
 191                 break;
 192         }
 193
 194         start = (video_rom_resource.end + 1 + 2047) & ~2047UL;
 195         if (start < upper)
 196                 start = upper;
 197
 198         /* system rom */
 199         request_resource(&iomem_resource, &system_rom_resource);
 200         upper = system_rom_resource.start;
 201
 202         /* check for extension rom (ignore length byte!) */
 203         rom = isa_bus_to_virt(extension_rom_resource.start);
 204         if (romsignature(rom)) {
 205                 length = extension_rom_resource.end - extension_rom_resource.start + 1;
 206                 if (romchecksum(rom, length)) {
 207                         request_resource(&iomem_resource, &extension_rom_resource);
 208                         upper = extension_rom_resource.start;
 209                 }
 210         }
 211
 212         /* check for adapter roms on 2k boundaries */
 213         for (i = 0; i < ARRAY_SIZE(adapter_rom_resources) && start < upper; start += 2048) {
 214                 rom = isa_bus_to_virt(start);
 215                 if (!romsignature(rom))
 216                         continue;
 217
 218                 /* 0 < length <= 0x7f * 512, historically */
 219                 length = rom[2] * 512;
 220
 221                 /* but accept any length that fits if checksum okay */
 222                 if (!length || start + length > upper || !romchecksum(rom, length))
 223                         continue;
 224
 225                 adapter_rom_resources[i].start = start;
 226                 adapter_rom_resources[i].end = start + length - 1;
 227                 request_resource(&iomem_resource, &adapter_rom_resources[i]);
 228
 229                 start = adapter_rom_resources[i++].end & ~2047UL;
 230         }
 231 }
 232
 233 /*
 234  * Request address space for all standard RAM and ROM resources
 235  * and also for regions reported as reserved by the e820.
 236  */
 237 static void __init
 238 legacy_init_iomem_resources(struct resource *code_resource, struct resource *data_resource)
 239 {
 240         int i;
 241
 242         probe_roms();
 243         for (i = 0; i < e820.nr_map; i++) {
 244                 struct resource *res;
 245 #ifndef CONFIG_RESOURCES_64BIT
 246                 if (e820.map[i].addr + e820.map[i].size > 0x100000000ULL)
 247                         continue;
 248 #endif
 249                 res = kzalloc(sizeof(struct resource), GFP_ATOMIC);
 250                 switch (e820.map[i].type) {
 251                 case E820_RAM:  res->name = "System RAM"; break;
 252                 case E820_ACPI: res->name = "ACPI Tables"; break;
 253                 case E820_NVS:  res->name = "ACPI Non-volatile Storage"; break;
 254                 default:        res->name = "reserved";
 255                 }
 256                 res->start = e820.map[i].addr;
 257                 res->end = res->start + e820.map[i].size - 1;
 258                 res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
 259                 if (request_resource(&iomem_resource, res)) {
 260                         kfree(res);
 261                         continue;
 262                 }
 263                 if (e820.map[i].type == E820_RAM) {
 264                         /*
 265                          *  We don't know which RAM region contains kernel data,
 266                          *  so we try it repeatedly and let the resource manager
 267                          *  test it.
 268                          */
 269                         request_resource(res, code_resource);
 270                         request_resource(res, data_resource);
 271 #ifdef CONFIG_KEXEC
 272                         request_resource(res, &crashk_res);
 273 #endif
 274                 }
 275         }
 276 }
 277
 278 /*
 279  * Request address space for all standard resources
 280  *
 281  * This is called just before pcibios_init(), which is also a
 282  * subsys_initcall, but is linked in later (in arch/i386/pci/common.c).
 283  */
 284 static int __init request_standard_resources(void)
 285 {
 286         int i;
 287
 288         printk("Setting up standard PCI resources\n");
 289         if (efi_enabled)
 290                 efi_initialize_iomem_resources(&code_resource, &data_resource);
 291         else
 292                 legacy_init_iomem_resources(&code_resource, &data_resource);
 293
 294         /* EFI systems may still have VGA */
 295         request_resource(&iomem_resource, &video_ram_resource);
 296
 297         /* request I/O space for devices used on all i[345]86 PCs */
 298         for (i = 0; i < ARRAY_SIZE(standard_io_resources); i++)
 299                 request_resource(&ioport_resource, &standard_io_resources[i]);
 300         return 0;
 301 }
 302
 303 subsys_initcall(request_standard_resources);
 304
 305 void __init add_memory_region(unsigned long long start,
 306                               unsigned long long size, int type)
 307 {
 308         int x;
 309
 310         if (!efi_enabled) {
 311                 x = e820.nr_map;
 312
 313                 if (x == E820MAX) {
 314                     printk(KERN_ERR "Ooops! Too many entries in the memory map!\n");
 315                     return;
 316                 }
 317
 318                 e820.map[x].addr = start;
 319                 e820.map[x].size = size;
 320                 e820.map[x].type = type;
 321                 e820.nr_map++;
 322         }
 323 } /* add_memory_region */
 324
 325 /*
 326  * Sanitize the BIOS e820 map.
 327  *
 328  * Some e820 responses include overlapping entries.  The following
 329  * replaces the original e820 map with a new one, removing overlaps.
 330  *
 331  */
 332 int __init sanitize_e820_map(struct e820entry * biosmap, char * pnr_map)
 333 {
 334         struct change_member *change_tmp;
 335         unsigned long current_type, last_type;
 336         unsigned long long last_addr;
 337         int chgidx, still_changing;
 338         int overlap_entries;
 339         int new_bios_entry;
 340         int old_nr, new_nr, chg_nr;
 341         int i;
 342
 343         /*
 344                 Visually we're performing the following (1,2,3,4 = memory types)...
 345
 346                 Sample memory map (w/overlaps):
 347                    ____22__________________
 348                    ______________________4_
 349                    ____1111________________
 350                    _44_____________________
 351                    11111111________________
 352                    ____________________33__
 353                    ___________44___________
 354                    __________33333_________
 355                    ______________22________
 356                    ___________________2222_
 357                    _________111111111______
 358                    _____________________11_
 359                    _________________4______
 360
 361                 Sanitized equivalent (no overlap):
 362                    1_______________________
 363                    _44_____________________
 364                    ___1____________________
 365                    ____22__________________
 366                    ______11________________
 367                    _________1______________
 368                    __________3_____________
 369                    ___________44___________
 370                    _____________33_________
 371                    _______________2________
 372                    ________________1_______
 373                    _________________4______
 374                    ___________________2____
 375                    ____________________33__
 376                    ______________________4_
 377         */
 378         printk("sanitize start\n");
 379         /* if there's only one memory region, don't bother */
 380         if (*pnr_map < 2) {
 381                 printk("sanitize bail 0\n");
 382                 return -1;
 383         }
 384
 385         old_nr = *pnr_map;
 386
 387         /* bail out if we find any unreasonable addresses in bios map */
 388         for (i=0; i<old_nr; i++)
 389                 if (biosmap[i].addr + biosmap[i].size < biosmap[i].addr) {
 390                         printk("sanitize bail 1\n");
 391                         return -1;
 392                 }
 393
 394         /* create pointers for initial change-point information (for sorting) */
 395         for (i=0; i < 2*old_nr; i++)
 396                 change_point[i] = &change_point_list[i];
 397
 398         /* record all known change-points (starting and ending addresses),
 399            omitting those that are for empty memory regions */
 400         chgidx = 0;
 401         for (i=0; i < old_nr; i++)      {
 402                 if (biosmap[i].size != 0) {
 403                         change_point[chgidx]->addr = biosmap[i].addr;
 404                         change_point[chgidx++]->pbios = &biosmap[i];
 405                         change_point[chgidx]->addr = biosmap[i].addr + biosmap[i].size;
 406                         change_point[chgidx++]->pbios = &biosmap[i];
 407                 }
 408         }
 409         chg_nr = chgidx;        /* true number of change-points */
 410
 411         /* sort change-point list by memory addresses (low -> high) */
 412         still_changing = 1;
 413         while (still_changing)  {
 414                 still_changing = 0;
 415                 for (i=1; i < chg_nr; i++)  {
 416                         /* if <current_addr> > <last_addr>, swap */
 417                         /* or, if current=<start_addr> & last=<end_addr>, swap */
 418                         if ((change_point[i]->addr < change_point[i-1]->addr) ||
 419                                 ((change_point[i]->addr == change_point[i-1]->addr) &&
 420                                  (change_point[i]->addr == change_point[i]->pbios->addr) &&
 421                                  (change_point[i-1]->addr != change_point[i-1]->pbios->addr))
 422                            )
 423                         {
 424                                 change_tmp = change_point[i];
 425                                 change_point[i] = change_point[i-1];
 426                                 change_point[i-1] = change_tmp;
 427                                 still_changing=1;
 428                         }
 429                 }
 430         }
 431
 432         /* create a new bios memory map, removing overlaps */
 433         overlap_entries=0;       /* number of entries in the overlap table */
 434         new_bios_entry=0;        /* index for creating new bios map entries */
 435         last_type = 0;           /* start with undefined memory type */
 436         last_addr = 0;           /* start with 0 as last starting address */
 437         /* loop through change-points, determining affect on the new bios map */
 438         for (chgidx=0; chgidx < chg_nr; chgidx++)
 439         {
 440                 /* keep track of all overlapping bios entries */
 441                 if (change_point[chgidx]->addr == change_point[chgidx]->pbios->addr)
 442                 {
 443                         /* add map entry to overlap list (> 1 entry implies an overlap) */
 444                         overlap_list[overlap_entries++]=change_point[chgidx]->pbios;
 445                 }
 446                 else
 447                 {
 448                         /* remove entry from list (order independent, so swap with last) */
 449                         for (i=0; i<overlap_entries; i++)
 450                         {
 451                                 if (overlap_list[i] == change_point[chgidx]->pbios)
 452                                         overlap_list[i] = overlap_list[overlap_entries-1];
 453                         }
 454                         overlap_entries--;
 455                 }
 456                 /* if there are overlapping entries, decide which "type" to use */
 457                 /* (larger value takes precedence -- 1=usable, 2,3,4,4+=unusable) */
 458                 current_type = 0;
 459                 for (i=0; i<overlap_entries; i++)
 460                         if (overlap_list[i]->type > current_type)
 461                                 current_type = overlap_list[i]->type;
 462                 /* continue building up new bios map based on this information */
 463                 if (current_type != last_type)  {
 464                         if (last_type != 0)      {
 465                                 new_bios[new_bios_entry].size =
 466                                         change_point[chgidx]->addr - last_addr;
 467                                 /* move forward only if the new size was non-zero */
 468                                 if (new_bios[new_bios_entry].size != 0)
 469                                         if (++new_bios_entry >= E820MAX)
 470                                                 break;  /* no more space left for new bios entries */
 471                         }
 472                         if (current_type != 0)  {
 473                                 new_bios[new_bios_entry].addr = change_point[chgidx]->addr;
 474                                 new_bios[new_bios_entry].type = current_type;
 475                                 last_addr=change_point[chgidx]->addr;
 476                         }
 477                         last_type = current_type;
 478                 }
 479         }
 480         new_nr = new_bios_entry;   /* retain count for new bios entries */
 481
 482         /* copy new bios mapping into original location */
 483         memcpy(biosmap, new_bios, new_nr*sizeof(struct e820entry));
 484         *pnr_map = new_nr;
 485
 486         printk("sanitize end\n");
 487         return 0;
 488 }
 489
 490 /*
 491  * Copy the BIOS e820 map into a safe place.
 492  *
 493  * Sanity-check it while we're at it..
 494  *
 495  * If we're lucky and live on a modern system, the setup code
 496  * will have given us a memory map that we can use to properly
 497  * set up memory.  If we aren't, we'll fake a memory map.
 498  *
 499  * We check to see that the memory map contains at least 2 elements
 500  * before we'll use it, because the detection code in setup.S may
 501  * not be perfect and most every PC known to man has two memory
 502  * regions: one from 0 to 640k, and one from 1mb up.  (The IBM
 503  * thinkpad 560x, for example, does not cooperate with the memory
 504  * detection code.)
 505  */
 506 int __init copy_e820_map(struct e820entry * biosmap, int nr_map)
 507 {
 508         /* Only one memory region (or negative)? Ignore it */
 509         if (nr_map < 2)
 510                 return -1;
 511
 512         do {
 513                 unsigned long long start = biosmap->addr;
 514                 unsigned long long size = biosmap->size;
 515                 unsigned long long end = start + size;
 516                 unsigned long type = biosmap->type;
 517                 printk("copy_e820_map() start: %016Lx size: %016Lx end: %016Lx type: %ld\n", start, size, end, type);
 518
 519                 /* Overflow in 64 bits? Ignore the memory map. */
 520                 if (start > end)
 521                         return -1;
 522
 523                 /*
 524                  * Some BIOSes claim RAM in the 640k - 1M region.
 525                  * Not right. Fix it up.
 526                  */
 527                 if (type == E820_RAM) {
 528                         printk("copy_e820_map() type is E820_RAM\n");
 529                         if (start < 0x100000ULL && end > 0xA0000ULL) {
 530                                 printk("copy_e820_map() lies in range...\n");
 531                                 if (start < 0xA0000ULL) {
 532                                         printk("copy_e820_map() start < 0xA0000ULL\n");
 533                                         add_memory_region(start, 0xA0000ULL-start, type);
 534                                 }
 535                                 if (end <= 0x100000ULL) {
 536                                         printk("copy_e820_map() end <= 0x100000ULL\n");
 537                                         continue;
 538                                 }
 539                                 start = 0x100000ULL;
 540                                 size = end - start;
 541                         }
 542                 }
 543                 add_memory_region(start, size, type);
 544         } while (biosmap++,--nr_map);
 545         return 0;
 546 }
 547
 548 /*
 549  * Callback for efi_memory_walk.
 550  */
 551 static int __init
 552 efi_find_max_pfn(unsigned long start, unsigned long end, void *arg)
 553 {
 554         unsigned long *max_pfn = arg, pfn;
 555
 556         if (start < end) {
 557                 pfn = PFN_UP(end -1);
 558                 if (pfn > *max_pfn)
 559                         *max_pfn = pfn;
 560         }
 561         return 0;
 562 }
 563
 564 static int __init
 565 efi_memory_present_wrapper(unsigned long start, unsigned long end, void *arg)
 566 {
 567         memory_present(0, PFN_UP(start), PFN_DOWN(end));
 568         return 0;
 569 }
 570
 571 /*
 572  * Find the highest page frame number we have available
 573  */
 574 void __init find_max_pfn(void)
 575 {
 576         int i;
 577
 578         max_pfn = 0;
 579         if (efi_enabled) {
 580                 efi_memmap_walk(efi_find_max_pfn, &max_pfn);
 581                 efi_memmap_walk(efi_memory_present_wrapper, NULL);
 582                 return;
 583         }
 584
 585         for (i = 0; i < e820.nr_map; i++) {
 586                 unsigned long start, end;
 587                 /* RAM? */
 588                 if (e820.map[i].type != E820_RAM)
 589                         continue;
 590                 start = PFN_UP(e820.map[i].addr);
 591                 end = PFN_DOWN(e820.map[i].addr + e820.map[i].size);
 592                 if (start >= end)
 593                         continue;
 594                 if (end > max_pfn)
 595                         max_pfn = end;
 596                 memory_present(0, start, end);
 597         }
 598 }
 599
 600 /*
 601  * Free all available memory for boot time allocation.  Used
 602  * as a callback function by efi_memory_walk()
 603  */
 604
 605 static int __init
 606 free_available_memory(unsigned long start, unsigned long end, void *arg)
 607 {
 608         /* check max_low_pfn */
 609         if (start >= (max_low_pfn << PAGE_SHIFT))
 610                 return 0;
 611         if (end >= (max_low_pfn << PAGE_SHIFT))
 612                 end = max_low_pfn << PAGE_SHIFT;
 613         if (start < end)
 614                 free_bootmem(start, end - start);
 615
 616         return 0;
 617 }
 618 /*
 619  * Register fully available low RAM pages with the bootmem allocator.
 620  */
 621 void __init register_bootmem_low_pages(unsigned long max_low_pfn)
 622 {
 623         int i;
 624
 625         if (efi_enabled) {
 626                 efi_memmap_walk(free_available_memory, NULL);
 627                 return;
 628         }
 629         for (i = 0; i < e820.nr_map; i++) {
 630                 unsigned long curr_pfn, last_pfn, size;
 631                 /*
 632                  * Reserve usable low memory
 633                  */
 634                 if (e820.map[i].type != E820_RAM)
 635                         continue;
 636                 /*
 637                  * We are rounding up the start address of usable memory:
 638                  */
 639                 curr_pfn = PFN_UP(e820.map[i].addr);
 640                 if (curr_pfn >= max_low_pfn)
 641                         continue;
 642                 /*
 643                  * ... and at the end of the usable range downwards:
 644                  */
 645                 last_pfn = PFN_DOWN(e820.map[i].addr + e820.map[i].size);
 646
 647                 if (last_pfn > max_low_pfn)
 648                         last_pfn = max_low_pfn;
 649
 650                 /*
 651                  * .. finally, did all the rounding and playing
 652                  * around just make the area go away?
 653                  */
 654                 if (last_pfn <= curr_pfn)
 655                         continue;
 656
 657                 size = last_pfn - curr_pfn;
 658                 free_bootmem(PFN_PHYS(curr_pfn), PFN_PHYS(size));
 659         }
 660 }
 661
 662 void __init register_memory(void)
 663 {
 664         unsigned long gapstart, gapsize, round;
 665         unsigned long long last;
 666         int i;
 667
 668         /*
 669          * Search for the bigest gap in the low 32 bits of the e820
 670          * memory space.
 671          */
 672         last = 0x100000000ull;
 673         gapstart = 0x10000000;
 674         gapsize = 0x400000;
 675         i = e820.nr_map;
 676         while (--i >= 0) {
 677                 unsigned long long start = e820.map[i].addr;
 678                 unsigned long long end = start + e820.map[i].size;
 679
 680                 /*
 681                  * Since "last" is at most 4GB, we know we'll
 682                  * fit in 32 bits if this condition is true
 683                  */
 684                 if (last > end) {
 685                         unsigned long gap = last - end;
 686
 687                         if (gap > gapsize) {
 688                                 gapsize = gap;
 689                                 gapstart = end;
 690                         }
 691                 }
 692                 if (start < last)
 693                         last = start;
 694         }
 695
 696         /*
 697          * See how much we want to round up: start off with
 698          * rounding to the next 1MB area.
 699          */
 700         round = 0x100000;
 701         while ((gapsize >> 4) > round)
 702                 round += round;
 703         /* Fun with two's complement */
 704         pci_mem_start = (gapstart + round) & -round;
 705
 706         printk("Allocating PCI resources starting at %08lx (gap: %08lx:%08lx)\n",
 707                 pci_mem_start, gapstart, gapsize);
 708 }