OvmfPkg/PlatformDxe/PlatformConfig.c

   1 /** @file
   2
   3   Utility functions for serializing (persistently storing) and deserializing
   4   OVMF's platform configuration.
   5
   6   Copyright (C) 2014, Red Hat, Inc.
   7
   8   This program and the accompanying materials are licensed and made available
   9   under the terms and conditions of the BSD License which accompanies this
  10   distribution. The full text of the license may be found at
  11   http://opensource.org/licenses/bsd-license.php
  12
  13   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
  14   WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  15
  16 **/
  17
  18 #include <Library/BaseMemoryLib.h>
  19 #include <Library/DebugLib.h>
  20 #include <Library/MemoryAllocationLib.h>
  21 #include <Library/UefiLib.h>
  22 #include <Library/UefiRuntimeServicesTableLib.h>
  23 #include <Guid/OvmfPlatformConfig.h>
  24
  25 #include "PlatformConfig.h"
  26
  27 //
  28 // Name of the UEFI variable that we use for persistent storage.
  29 //
  30 STATIC CHAR16 mVariableName[] = L"PlatformConfig";
  31
  32
  33 /**
  34   Serialize and persistently save platform configuration.
  35
  36   @param[in] PlatformConfig  The platform configuration to serialize and save.
  37
  38   @return  Status codes returned by gRT->SetVariable().
  39 **/
  40 EFI_STATUS
  41 EFIAPI
  42 PlatformConfigSave (
  43   IN PLATFORM_CONFIG *PlatformConfig
  44   )
  45 {
  46   EFI_STATUS Status;
  47
  48   //
  49   // We could implement any kind of translation here, as part of serialization.
  50   // For example, we could expose the platform configuration in separate
  51   // variables with human-readable contents, allowing other tools to access
  52   // them more easily. For now, just save a binary dump.
  53   //
  54   Status = gRT->SetVariable (mVariableName, &gOvmfPlatformConfigGuid,
  55                   EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS |
  56                     EFI_VARIABLE_RUNTIME_ACCESS,
  57                   sizeof *PlatformConfig, PlatformConfig);
  58   return Status;
  59 }
  60
  61
  62 /**
  63   Load and deserialize platform configuration.
  64
  65   When the function fails, output parameters are indeterminate.
  66
  67   @param[out] PlatformConfig    The platform configuration to receive the
  68                                 loaded data.
  69
  70   @param[out] OptionalElements  This bitmap describes the presence of optional
  71                                 configuration elements that have been loaded.
  72                                 PLATFORM_CONFIG_F_DOWNGRADE means that some
  73                                 unknown elements, present in the wire format,
  74                                 have been ignored.
  75
  76   @retval  EFI_SUCCESS         Loading & deserialization successful.
  77   @return                      Error codes returned by GetVariable2().
  78 **/
  79 EFI_STATUS
  80 EFIAPI
  81 PlatformConfigLoad (
  82   OUT PLATFORM_CONFIG *PlatformConfig,
  83   OUT UINT64          *OptionalElements
  84   )
  85 {
  86   VOID       *Data;
  87   UINTN      DataSize;
  88   EFI_STATUS Status;
  89
  90   //
  91   // Any translation done in PlatformConfigSave() would have to be mirrored
  92   // here. For now, just load the binary dump.
  93   //
  94   // Versioning of the binary wire format is implemented based on size
  95   // (only incremental changes, ie. new fields), and on GUID.
  96   // (Incompatible changes require a GUID change.)
  97   //
  98   Status = GetVariable2 (mVariableName, &gOvmfPlatformConfigGuid, &Data,
  99              &DataSize);
 100   if (EFI_ERROR (Status)) {
 101     return Status;
 102   }
 103
 104   *OptionalElements = 0;
 105   if (DataSize > sizeof *PlatformConfig) {
 106     //
 107     // Handle firmware downgrade -- keep only leading part.
 108     //
 109     CopyMem (PlatformConfig, Data, sizeof *PlatformConfig);
 110     *OptionalElements |= PLATFORM_CONFIG_F_DOWNGRADE;
 111   } else {
 112     CopyMem (PlatformConfig, Data, DataSize);
 113
 114     //
 115     // Handle firmware upgrade -- zero out missing fields.
 116     //
 117     ZeroMem ((UINT8 *)PlatformConfig + DataSize,
 118       sizeof *PlatformConfig - DataSize);
 119   }
 120
 121   //
 122   // Based on DataSize, report the optional features that we recognize.
 123   //
 124   if (DataSize >= (OFFSET_OF (PLATFORM_CONFIG, VerticalResolution) +
 125                    sizeof PlatformConfig->VerticalResolution)) {
 126     *OptionalElements |= PLATFORM_CONFIG_F_GRAPHICS_RESOLUTION;
 127   }
 128
 129   FreePool (Data);
 130   return EFI_SUCCESS;
 131 }