ArmVirtPkg/VirtFdtDxe/VirtFdtDxe.c

   1 /** @file
   2 *  Device tree enumeration DXE driver for ARM Virtual Machines
   3 *
   4 *  Copyright (c) 2014, Linaro Ltd. All rights reserved.<BR>
   5 *
   6 *  This program and the accompanying materials are
   7 *  licensed and made available under the terms and conditions of the BSD License
   8 *  which accompanies this distribution.  The full text of the license may be found at
   9 *  http://opensource.org/licenses/bsd-license.php
  10 *
  11 *  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  12 *  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  13 *
  14 **/
  15
  16 #include <Library/BaseLib.h>
  17 #include <Library/DebugLib.h>
  18 #include <Library/UefiLib.h>
  19 #include <Library/BaseMemoryLib.h>
  20 #include <Library/UefiDriverEntryPoint.h>
  21 #include <Library/MemoryAllocationLib.h>
  22 #include <Library/UefiBootServicesTableLib.h>
  23 #include <Library/VirtioMmioDeviceLib.h>
  24 #include <Library/DevicePathLib.h>
  25 #include <Library/PcdLib.h>
  26 #include <Library/DxeServicesLib.h>
  27 #include <Library/HobLib.h>
  28 #include <libfdt.h>
  29 #include <Library/XenIoMmioLib.h>
  30
  31 #include <Guid/Fdt.h>
  32 #include <Guid/VirtioMmioTransport.h>
  33 #include <Guid/FdtHob.h>
  34
  35 #pragma pack (1)
  36 typedef struct {
  37   VENDOR_DEVICE_PATH                  Vendor;
  38   UINT64                              PhysBase;
  39   EFI_DEVICE_PATH_PROTOCOL            End;
  40 } VIRTIO_TRANSPORT_DEVICE_PATH;
  41 #pragma pack ()
  42
  43 typedef enum {
  44   PropertyTypeUnknown,
  45   PropertyTypeRtc,
  46   PropertyTypeVirtio,
  47   PropertyTypeUart,
  48   PropertyTypeTimer,
  49   PropertyTypeFwCfg,
  50   PropertyTypePciHost,
  51   PropertyTypeXen,
  52 } PROPERTY_TYPE;
  53
  54 typedef struct {
  55   PROPERTY_TYPE Type;
  56   CHAR8         Compatible[32];
  57 } PROPERTY;
  58
  59 STATIC CONST PROPERTY CompatibleProperties[] = {
  60   { PropertyTypeRtc,     "arm,pl031"             },
  61   { PropertyTypeVirtio,  "virtio,mmio"           },
  62   { PropertyTypeUart,    "arm,pl011"             },
  63   { PropertyTypeTimer,   "arm,armv7-timer"       },
  64   { PropertyTypeTimer,   "arm,armv8-timer"       },
  65   { PropertyTypeFwCfg,   "qemu,fw-cfg-mmio"      },
  66   { PropertyTypePciHost, "pci-host-ecam-generic" },
  67   { PropertyTypeXen,     "xen,xen"               },
  68   { PropertyTypeUnknown, ""                      }
  69 };
  70
  71 typedef struct {
  72   UINT32  Type;
  73   UINT32  Number;
  74   UINT32  Flags;
  75 } INTERRUPT_PROPERTY;
  76
  77 STATIC
  78 PROPERTY_TYPE
  79 GetTypeFromNode (
  80   IN CONST CHAR8 *NodeType,
  81   IN UINTN       Size
  82   )
  83 {
  84   CONST CHAR8    *Compatible;
  85   CONST PROPERTY *CompatibleProperty;
  86
  87   //
  88   // A 'compatible' node may contain a sequence of NULL terminated
  89   // compatible strings so check each one
  90   //
  91   for (Compatible = NodeType; Compatible < NodeType + Size && *Compatible;
  92        Compatible += 1 + AsciiStrLen (Compatible)) {
  93     for (CompatibleProperty = CompatibleProperties; CompatibleProperty->Compatible[0]; CompatibleProperty++) {
  94       if (AsciiStrCmp (CompatibleProperty->Compatible, Compatible) == 0) {
  95         return CompatibleProperty->Type;
  96       }
  97     }
  98   }
  99   return PropertyTypeUnknown;
 100 }
 101
 102 //
 103 // We expect the "ranges" property of "pci-host-ecam-generic" to consist of
 104 // records like this.
 105 //
 106 #pragma pack (1)
 107 typedef struct {
 108   UINT32 Type;
 109   UINT64 ChildBase;
 110   UINT64 CpuBase;
 111   UINT64 Size;
 112 } DTB_PCI_HOST_RANGE_RECORD;
 113 #pragma pack ()
 114
 115 #define DTB_PCI_HOST_RANGE_RELOCATABLE  BIT31
 116 #define DTB_PCI_HOST_RANGE_PREFETCHABLE BIT30
 117 #define DTB_PCI_HOST_RANGE_ALIASED      BIT29
 118 #define DTB_PCI_HOST_RANGE_MMIO32       BIT25
 119 #define DTB_PCI_HOST_RANGE_MMIO64       (BIT25 | BIT24)
 120 #define DTB_PCI_HOST_RANGE_IO           BIT24
 121 #define DTB_PCI_HOST_RANGE_TYPEMASK     (BIT31 | BIT30 | BIT29 | BIT25 | BIT24)
 122
 123 /**
 124   Process the device tree node describing the generic PCI host controller.
 125
 126   param[in] DeviceTreeBase  Pointer to the device tree.
 127
 128   param[in] Node            Offset of the device tree node whose "compatible"
 129                             property is "pci-host-ecam-generic".
 130
 131   param[in] RegProp         Pointer to the "reg" property of Node. The caller
 132                             is responsible for ensuring that the size of the
 133                             property is 4 UINT32 cells.
 134
 135   @retval EFI_SUCCESS         Parsing successful, properties parsed from Node
 136                               have been stored in dynamic PCDs.
 137
 138   @retval EFI_PROTOCOL_ERROR  Parsing failed. PCDs are left unchanged.
 139 **/
 140 STATIC
 141 EFI_STATUS
 142 EFIAPI
 143 ProcessPciHost (
 144   IN CONST VOID *DeviceTreeBase,
 145   IN INT32      Node,
 146   IN CONST VOID *RegProp
 147   )
 148 {
 149   UINT64     ConfigBase, ConfigSize;
 150   CONST VOID *Prop;
 151   INT32      Len;
 152   UINT32     BusMin, BusMax;
 153   UINT32     RecordIdx;
 154   UINT64     IoBase, IoSize, IoTranslation;
 155   UINT64     MmioBase, MmioSize, MmioTranslation;
 156
 157   //
 158   // Fetch the ECAM window.
 159   //
 160   ConfigBase = fdt64_to_cpu (((CONST UINT64 *)RegProp)[0]);
 161   ConfigSize = fdt64_to_cpu (((CONST UINT64 *)RegProp)[1]);
 162
 163   //
 164   // Fetch the bus range (note: inclusive).
 165   //
 166   Prop = fdt_getprop (DeviceTreeBase, Node, "bus-range", &Len);
 167   if (Prop == NULL || Len != 2 * sizeof(UINT32)) {
 168     DEBUG ((EFI_D_ERROR, "%a: 'bus-range' not found or invalid\n",
 169       __FUNCTION__));
 170     return EFI_PROTOCOL_ERROR;
 171   }
 172   BusMin = fdt32_to_cpu (((CONST UINT32 *)Prop)[0]);
 173   BusMax = fdt32_to_cpu (((CONST UINT32 *)Prop)[1]);
 174
 175   //
 176   // Sanity check: the config space must accommodate all 4K register bytes of
 177   // all 8 functions of all 32 devices of all buses.
 178   //
 179   if (BusMax < BusMin || BusMax - BusMin == MAX_UINT32 ||
 180       DivU64x32 (ConfigSize, SIZE_4KB * 8 * 32) < BusMax - BusMin + 1) {
 181     DEBUG ((EFI_D_ERROR, "%a: invalid 'bus-range' and/or 'reg'\n",
 182       __FUNCTION__));
 183     return EFI_PROTOCOL_ERROR;
 184   }
 185
 186   //
 187   // Iterate over "ranges".
 188   //
 189   Prop = fdt_getprop (DeviceTreeBase, Node, "ranges", &Len);
 190   if (Prop == NULL || Len == 0 ||
 191       Len % sizeof (DTB_PCI_HOST_RANGE_RECORD) != 0) {
 192     DEBUG ((EFI_D_ERROR, "%a: 'ranges' not found or invalid\n", __FUNCTION__));
 193     return EFI_PROTOCOL_ERROR;
 194   }
 195
 196   //
 197   // IoBase, IoTranslation, MmioBase and MmioTranslation are initialized only
 198   // in order to suppress '-Werror=maybe-uninitialized' warnings *incorrectly*
 199   // emitted by some gcc versions.
 200   //
 201   IoBase = 0;
 202   IoTranslation = 0;
 203   MmioBase = 0;
 204   MmioTranslation = 0;
 205
 206   //
 207   // IoSize and MmioSize are initialized to zero because the logic below
 208   // requires it.
 209   //
 210   IoSize = 0;
 211   MmioSize = 0;
 212   for (RecordIdx = 0; RecordIdx < Len / sizeof (DTB_PCI_HOST_RANGE_RECORD);
 213        ++RecordIdx) {
 214     CONST DTB_PCI_HOST_RANGE_RECORD *Record;
 215
 216     Record = (CONST DTB_PCI_HOST_RANGE_RECORD *)Prop + RecordIdx;
 217     switch (fdt32_to_cpu (Record->Type) & DTB_PCI_HOST_RANGE_TYPEMASK) {
 218     case DTB_PCI_HOST_RANGE_IO:
 219       IoBase = fdt64_to_cpu (Record->ChildBase);
 220       IoSize = fdt64_to_cpu (Record->Size);
 221       IoTranslation = fdt64_to_cpu (Record->CpuBase) - IoBase;
 222       break;
 223
 224     case DTB_PCI_HOST_RANGE_MMIO32:
 225       MmioBase = fdt64_to_cpu (Record->ChildBase);
 226       MmioSize = fdt64_to_cpu (Record->Size);
 227       MmioTranslation = fdt64_to_cpu (Record->CpuBase) - MmioBase;
 228
 229       if (MmioBase > MAX_UINT32 || MmioSize > MAX_UINT32 ||
 230           MmioBase + MmioSize > SIZE_4GB) {
 231         DEBUG ((EFI_D_ERROR, "%a: MMIO32 space invalid\n", __FUNCTION__));
 232         return EFI_PROTOCOL_ERROR;
 233       }
 234
 235       if (MmioTranslation != 0) {
 236         DEBUG ((EFI_D_ERROR, "%a: unsupported nonzero MMIO32 translation "
 237           "0x%Lx\n", __FUNCTION__, MmioTranslation));
 238         return EFI_UNSUPPORTED;
 239       }
 240
 241       break;
 242     }
 243   }
 244   if (IoSize == 0 || MmioSize == 0) {
 245     DEBUG ((EFI_D_ERROR, "%a: %a space empty\n", __FUNCTION__,
 246       (IoSize == 0) ? "IO" : "MMIO32"));
 247     return EFI_PROTOCOL_ERROR;
 248   }
 249
 250   PcdSet64 (PcdPciExpressBaseAddress, ConfigBase);
 251
 252   PcdSet32 (PcdPciBusMin, BusMin);
 253   PcdSet32 (PcdPciBusMax, BusMax);
 254
 255   PcdSet64 (PcdPciIoBase,        IoBase);
 256   PcdSet64 (PcdPciIoSize,        IoSize);
 257   PcdSet64 (PcdPciIoTranslation, IoTranslation);
 258
 259   PcdSet32 (PcdPciMmio32Base, (UINT32)MmioBase);
 260   PcdSet32 (PcdPciMmio32Size, (UINT32)MmioSize);
 261
 262   PcdSetBool (PcdPciDisableBusEnumeration, FALSE);
 263
 264   DEBUG ((EFI_D_INFO, "%a: Config[0x%Lx+0x%Lx) Bus[0x%x..0x%x] "
 265     "Io[0x%Lx+0x%Lx)@0x%Lx Mem[0x%Lx+0x%Lx)@0x%Lx\n", __FUNCTION__, ConfigBase,
 266     ConfigSize, BusMin, BusMax, IoBase, IoSize, IoTranslation, MmioBase,
 267     MmioSize, MmioTranslation));
 268   return EFI_SUCCESS;
 269 }
 270
 271
 272 EFI_STATUS
 273 EFIAPI
 274 InitializeVirtFdtDxe (
 275   IN EFI_HANDLE           ImageHandle,
 276   IN EFI_SYSTEM_TABLE     *SystemTable
 277   )
 278 {
 279   VOID                           *Hob;
 280   VOID                           *DeviceTreeBase;
 281   INT32                          Node, Prev;
 282   INT32                          RtcNode;
 283   EFI_STATUS                     Status;
 284   CONST CHAR8                    *Type;
 285   INT32                          Len;
 286   PROPERTY_TYPE                  PropType;
 287   CONST VOID                     *RegProp;
 288   VIRTIO_TRANSPORT_DEVICE_PATH   *DevicePath;
 289   EFI_HANDLE                     Handle;
 290   UINT64                         RegBase;
 291   CONST INTERRUPT_PROPERTY       *InterruptProp;
 292   INT32                          SecIntrNum, IntrNum, VirtIntrNum, HypIntrNum;
 293   UINT64                         FwCfgSelectorAddress;
 294   UINT64                         FwCfgSelectorSize;
 295   UINT64                         FwCfgDataAddress;
 296   UINT64                         FwCfgDataSize;
 297   UINT64                         FwCfgDmaAddress;
 298   UINT64                         FwCfgDmaSize;
 299   BOOLEAN                        HavePci;
 300
 301   Hob = GetFirstGuidHob(&gFdtHobGuid);
 302   if (Hob == NULL || GET_GUID_HOB_DATA_SIZE (Hob) != sizeof (UINT64)) {
 303     return EFI_NOT_FOUND;
 304   }
 305   DeviceTreeBase = (VOID *)(UINTN)*(UINT64 *)GET_GUID_HOB_DATA (Hob);
 306
 307   if (fdt_check_header (DeviceTreeBase) != 0) {
 308     DEBUG ((EFI_D_ERROR, "%a: No DTB found @ 0x%p\n", __FUNCTION__, DeviceTreeBase));
 309     return EFI_NOT_FOUND;
 310   }
 311
 312   DEBUG ((EFI_D_INFO, "%a: DTB @ 0x%p\n", __FUNCTION__, DeviceTreeBase));
 313
 314   RtcNode = -1;
 315   HavePci = FALSE;
 316   //
 317   // Now enumerate the nodes and install peripherals that we are interested in,
 318   // i.e., GIC, RTC and virtio MMIO nodes
 319   //
 320   for (Prev = 0;; Prev = Node) {
 321     Node = fdt_next_node (DeviceTreeBase, Prev, NULL);
 322     if (Node < 0) {
 323       break;
 324     }
 325
 326     Type = fdt_getprop (DeviceTreeBase, Node, "compatible", &Len);
 327     if (Type == NULL) {
 328       continue;
 329     }
 330
 331     PropType = GetTypeFromNode (Type, Len);
 332     if (PropType == PropertyTypeUnknown) {
 333       continue;
 334     }
 335
 336     //
 337     // Get the 'reg' property of this node. For now, we will assume
 338     // 8 byte quantities for base and size, respectively.
 339     // TODO use #cells root properties instead
 340     //
 341     RegProp = fdt_getprop (DeviceTreeBase, Node, "reg", &Len);
 342     ASSERT ((RegProp != NULL) || (PropType == PropertyTypeTimer));
 343
 344     switch (PropType) {
 345     case PropertyTypePciHost:
 346       ASSERT (Len == 2 * sizeof (UINT64));
 347       Status = ProcessPciHost (DeviceTreeBase, Node, RegProp);
 348       ASSERT_EFI_ERROR (Status);
 349       HavePci = TRUE;
 350       break;
 351
 352     case PropertyTypeFwCfg:
 353       ASSERT (Len == 2 * sizeof (UINT64));
 354
 355       FwCfgDataAddress     = fdt64_to_cpu (((UINT64 *)RegProp)[0]);
 356       FwCfgDataSize        = 8;
 357       FwCfgSelectorAddress = FwCfgDataAddress + FwCfgDataSize;
 358       FwCfgSelectorSize    = 2;
 359
 360       //
 361       // The following ASSERT()s express
 362       //
 363       //   Address + Size - 1 <= MAX_UINTN
 364       //
 365       // for both registers, that is, that the last byte in each MMIO range is
 366       // expressible as a MAX_UINTN. The form below is mathematically
 367       // equivalent, and it also prevents any unsigned overflow before the
 368       // comparison.
 369       //
 370       ASSERT (FwCfgSelectorAddress <= MAX_UINTN - FwCfgSelectorSize + 1);
 371       ASSERT (FwCfgDataAddress     <= MAX_UINTN - FwCfgDataSize     + 1);
 372
 373       PcdSet64 (PcdFwCfgSelectorAddress, FwCfgSelectorAddress);
 374       PcdSet64 (PcdFwCfgDataAddress,     FwCfgDataAddress);
 375
 376       DEBUG ((EFI_D_INFO, "Found FwCfg @ 0x%Lx/0x%Lx\n", FwCfgSelectorAddress,
 377         FwCfgDataAddress));
 378
 379       if (fdt64_to_cpu (((UINT64 *)RegProp)[1]) >= 0x18) {
 380         FwCfgDmaAddress = FwCfgDataAddress + 0x10;
 381         FwCfgDmaSize    = 0x08;
 382
 383         //
 384         // See explanation above.
 385         //
 386         ASSERT (FwCfgDmaAddress <= MAX_UINTN - FwCfgDmaSize + 1);
 387
 388         PcdSet64 (PcdFwCfgDmaAddress, FwCfgDmaAddress);
 389         DEBUG ((EFI_D_INFO, "Found FwCfg DMA @ 0x%Lx\n", FwCfgDmaAddress));
 390       }
 391       break;
 392
 393     case PropertyTypeVirtio:
 394       ASSERT (Len == 16);
 395       //
 396       // Create a unique device path for this transport on the fly
 397       //
 398       RegBase = fdt64_to_cpu (((UINT64 *)RegProp)[0]);
 399       DevicePath = (VIRTIO_TRANSPORT_DEVICE_PATH *)CreateDeviceNode (
 400                                     HARDWARE_DEVICE_PATH,
 401                                     HW_VENDOR_DP,
 402                                     sizeof (VIRTIO_TRANSPORT_DEVICE_PATH));
 403       if (DevicePath == NULL) {
 404         DEBUG ((EFI_D_ERROR, "%a: Out of memory\n", __FUNCTION__));
 405         break;
 406       }
 407
 408       CopyMem (&DevicePath->Vendor.Guid, &gVirtioMmioTransportGuid,
 409         sizeof (EFI_GUID));
 410       DevicePath->PhysBase = RegBase;
 411       SetDevicePathNodeLength (&DevicePath->Vendor,
 412                                sizeof (*DevicePath) - sizeof (DevicePath->End));
 413       SetDevicePathEndNode (&DevicePath->End);
 414
 415       Handle = NULL;
 416       Status = gBS->InstallProtocolInterface (&Handle,
 417                      &gEfiDevicePathProtocolGuid, EFI_NATIVE_INTERFACE,
 418                      DevicePath);
 419       if (EFI_ERROR (Status)) {
 420         DEBUG ((EFI_D_ERROR, "%a: Failed to install the EFI_DEVICE_PATH "
 421           "protocol on a new handle (Status == %r)\n",
 422           __FUNCTION__, Status));
 423         FreePool (DevicePath);
 424         break;
 425       }
 426
 427       Status = VirtioMmioInstallDevice (RegBase, Handle);
 428       if (EFI_ERROR (Status)) {
 429         DEBUG ((EFI_D_ERROR, "%a: Failed to install VirtIO transport @ 0x%Lx "
 430           "on handle %p (Status == %r)\n", __FUNCTION__, RegBase,
 431           Handle, Status));
 432
 433         Status = gBS->UninstallProtocolInterface (Handle,
 434                         &gEfiDevicePathProtocolGuid, DevicePath);
 435         ASSERT_EFI_ERROR (Status);
 436         FreePool (DevicePath);
 437       }
 438       break;
 439
 440     case PropertyTypeRtc:
 441       ASSERT (Len == 16);
 442
 443       RegBase = fdt64_to_cpu (((UINT64 *)RegProp)[0]);
 444       ASSERT (RegBase < MAX_UINT32);
 445
 446       PcdSet32 (PcdPL031RtcBase, (UINT32)RegBase);
 447
 448       DEBUG ((EFI_D_INFO, "Found PL031 RTC @ 0x%Lx\n", RegBase));
 449       RtcNode = Node;
 450       break;
 451
 452     case PropertyTypeTimer:
 453       //
 454       // - interrupts : Interrupt list for secure, non-secure, virtual and
 455       //  hypervisor timers, in that order.
 456       //
 457       InterruptProp = fdt_getprop (DeviceTreeBase, Node, "interrupts", &Len);
 458       ASSERT (Len == 36 || Len == 48);
 459
 460       SecIntrNum = fdt32_to_cpu (InterruptProp[0].Number)
 461                    + (InterruptProp[0].Type ? 16 : 0);
 462       IntrNum = fdt32_to_cpu (InterruptProp[1].Number)
 463                 + (InterruptProp[1].Type ? 16 : 0);
 464       VirtIntrNum = fdt32_to_cpu (InterruptProp[2].Number)
 465                     + (InterruptProp[2].Type ? 16 : 0);
 466       HypIntrNum = Len < 48 ? 0 : fdt32_to_cpu (InterruptProp[3].Number)
 467                                   + (InterruptProp[3].Type ? 16 : 0);
 468
 469       DEBUG ((EFI_D_INFO, "Found Timer interrupts %d, %d, %d, %d\n",
 470         SecIntrNum, IntrNum, VirtIntrNum, HypIntrNum));
 471
 472       PcdSet32 (PcdArmArchTimerSecIntrNum, SecIntrNum);
 473       PcdSet32 (PcdArmArchTimerIntrNum, IntrNum);
 474       PcdSet32 (PcdArmArchTimerVirtIntrNum, VirtIntrNum);
 475       PcdSet32 (PcdArmArchTimerHypIntrNum, HypIntrNum);
 476       break;
 477
 478     case PropertyTypeXen:
 479       ASSERT (Len == 16);
 480
 481       //
 482       // Retrieve the reg base from this node and wire it up to the
 483       // MMIO flavor of the XenBus root device I/O protocol
 484       //
 485       RegBase = fdt64_to_cpu (((UINT64 *)RegProp)[0]);
 486       Handle = NULL;
 487       Status = XenIoMmioInstall (&Handle, RegBase);
 488       if (EFI_ERROR (Status)) {
 489         DEBUG ((EFI_D_ERROR, "%a: XenIoMmioInstall () failed on a new handle "
 490           "(Status == %r)\n", __FUNCTION__, Status));
 491         break;
 492       }
 493
 494       DEBUG ((EFI_D_INFO, "Found Xen node with Grant table @ 0x%Lx\n", RegBase));
 495
 496       break;
 497
 498     default:
 499       break;
 500     }
 501   }
 502
 503   if (!FeaturePcdGet (PcdPureAcpiBoot)) {
 504     //
 505     // Only install the FDT as a configuration table if we want to leave it up
 506     // to the OS to decide whether it prefers ACPI over DT.
 507     //
 508     Status = gBS->InstallConfigurationTable (&gFdtTableGuid, DeviceTreeBase);
 509     ASSERT_EFI_ERROR (Status);
 510
 511     //
 512     // UEFI takes ownership of the RTC hardware, and exposes its functionality
 513     // through the UEFI Runtime Services GetTime, SetTime, etc. This means we
 514     // need to disable it in the device tree to prevent the OS from attaching its
 515     // device driver as well.
 516     //
 517     if ((RtcNode != -1) &&
 518         fdt_setprop_string (DeviceTreeBase, RtcNode, "status",
 519           "disabled") != 0) {
 520       DEBUG ((EFI_D_WARN, "Failed to set PL031 status to 'disabled'\n"));
 521     }
 522
 523     if (HavePci) {
 524       //
 525       // Set the /chosen/linux,pci-probe-only property to 1, so that the PCI
 526       // setup we will perform in the firmware is honored by the Linux OS,
 527       // rather than torn down and done from scratch. This is generally a more
 528       // sensible approach, and aligns with what ACPI based OSes do in general.
 529       //
 530       // In case we are exposing an emulated VGA PCI device to the guest, which
 531       // may subsequently get exposed via the Graphics Output protocol and
 532       // driven as an efifb by Linux, we need this setting to prevent the
 533       // framebuffer from becoming unresponsive.
 534       //
 535       Node = fdt_path_offset (DeviceTreeBase, "/chosen");
 536       if (Node < 0) {
 537         Node = fdt_add_subnode (DeviceTreeBase, 0, "/chosen");
 538       }
 539       if (Node < 0 ||
 540           fdt_setprop_u32 (DeviceTreeBase, Node, "linux,pci-probe-only", 1) < 0) {
 541         DEBUG ((EFI_D_WARN, "Failed to set /chosen/linux,pci-probe-only property\n"));
 542       }
 543     }
 544   }
 545   return EFI_SUCCESS;
 546 }