ui/display/util/edid_parser.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "ui/display/util/edid_parser.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/hash.h"
  10 #include "base/strings/string_util.h"
  11 #include "base/sys_byteorder.h"
  12 #include "ui/gfx/geometry/size.h"
  13
  14 namespace ui {
  15
  16 namespace {
  17
  18 // Returns 64-bit persistent ID for the specified manufacturer's ID and
  19 // product_code_hash, and the index of the output it is connected to.
  20 // |output_index| is used to distinguish the displays of the same type. For
  21 // example, swapping two identical display between two outputs will not be
  22 // treated as swap. The 'serial number' field in EDID isn't used here because
  23 // it is not guaranteed to have unique number and it may have the same fixed
  24 // value (like 0).
  25 int64_t GetID(uint16_t manufacturer_id,
  26               uint32_t product_code_hash,
  27               uint8_t output_index) {
  28   return ((static_cast<int64_t>(manufacturer_id) << 40) |
  29           (static_cast<int64_t>(product_code_hash) << 8) | output_index);
  30 }
  31
  32 }  // namespace
  33
  34 bool GetDisplayIdFromEDID(const std::vector<uint8_t>& edid,
  35                           uint8_t output_index,
  36                           int64_t* display_id_out) {
  37   uint16_t manufacturer_id = 0;
  38   std::string product_name;
  39
  40   // ParseOutputDeviceData fails if it doesn't have product_name.
  41   ParseOutputDeviceData(edid, &manufacturer_id, &product_name, nullptr,
  42                         nullptr);
  43
  44   // Generates product specific value from product_name instead of product code.
  45   // See crbug.com/240341
  46   uint32_t product_code_hash = product_name.empty() ?
  47       0 : base::Hash(product_name);
  48   if (manufacturer_id != 0) {
  49     // An ID based on display's index will be assigned later if this call
  50     // fails.
  51     *display_id_out = GetID(
  52         manufacturer_id, product_code_hash, output_index);
  53     return true;
  54   }
  55   return false;
  56 }
  57
  58 bool ParseOutputDeviceData(const std::vector<uint8_t>& edid,
  59                            uint16_t* manufacturer_id,
  60                            std::string* human_readable_name,
  61                            gfx::Size* active_pixel_out,
  62                            gfx::Size* physical_display_size_out) {
  63   // See http://en.wikipedia.org/wiki/Extended_display_identification_data
  64   // for the details of EDID data format.  We use the following data:
  65   //   bytes 8-9: manufacturer EISA ID, in big-endian
  66   //   bytes 54-125: four descriptors (18-bytes each) which may contain
  67   //     the display name.
  68   const unsigned int kManufacturerOffset = 8;
  69   const unsigned int kManufacturerLength = 2;
  70   const unsigned int kDescriptorOffset = 54;
  71   const unsigned int kNumDescriptors = 4;
  72   const unsigned int kDescriptorLength = 18;
  73   // The specifier types.
  74   const unsigned char kMonitorNameDescriptor = 0xfc;
  75
  76   if (manufacturer_id) {
  77     if (edid.size() < kManufacturerOffset + kManufacturerLength) {
  78       LOG(ERROR) << "too short EDID data: manifacturer id";
  79       return false;
  80     }
  81
  82     *manufacturer_id =
  83         *reinterpret_cast<const uint16_t*>(&edid[kManufacturerOffset]);
  84 #if defined(ARCH_CPU_LITTLE_ENDIAN)
  85     *manufacturer_id = base::ByteSwap(*manufacturer_id);
  86 #endif
  87   }
  88
  89   if (human_readable_name)
  90     human_readable_name->clear();
  91
  92   for (unsigned int i = 0; i < kNumDescriptors; ++i) {
  93     if (edid.size() < kDescriptorOffset + (i + 1) * kDescriptorLength)
  94       break;
  95
  96     size_t offset = kDescriptorOffset + i * kDescriptorLength;
  97
  98     // Detailed Timing Descriptor:
  99     if (edid[offset] != 0 && edid[offset + 1] != 0) {
 100       const int kMaxResolution = 10080;  // 8k display.
 101
 102       if (active_pixel_out) {
 103         const int kHorizontalPixelLsbOffset = 2;
 104         const int kHorizontalPixelMsbOffset = 4;
 105         const int kVerticalPixelLsbOffset = 5;
 106         const int kVerticalPixelMsbOffset = 7;
 107
 108         int h_lsb = edid[offset + kHorizontalPixelLsbOffset];
 109         int h_msb = edid[offset + kHorizontalPixelMsbOffset];
 110         int h_pixel = std::min(h_lsb + ((h_msb & 0xF0) << 4), kMaxResolution);
 111
 112         int v_lsb = edid[offset + kVerticalPixelLsbOffset];
 113         int v_msb = edid[offset + kVerticalPixelMsbOffset];
 114         int v_pixel = std::min(v_lsb + ((v_msb & 0xF0) << 4), kMaxResolution);
 115
 116         active_pixel_out->SetSize(h_pixel, v_pixel);
 117         // EDID may contain multiple DTD. Use first one that
 118         // contains the highest resolution.
 119         active_pixel_out = nullptr;
 120       }
 121
 122       if (physical_display_size_out) {
 123         const int kHorizontalSizeLsbOffset = 12;
 124         const int kVerticalSizeLsbOffset = 13;
 125         const int kSizeMsbOffset = 14;
 126
 127         int h_lsb = edid[offset + kHorizontalSizeLsbOffset];
 128         int v_lsb = edid[offset + kVerticalSizeLsbOffset];
 129
 130         int msb = edid[offset + kSizeMsbOffset];
 131         int h_size = h_lsb + ((msb & 0xF0) << 4);
 132         int v_size = v_lsb + ((msb & 0x0F) << 8);
 133         physical_display_size_out->SetSize(h_size, v_size);
 134         physical_display_size_out = nullptr;
 135       }
 136       continue;
 137     }
 138
 139     // EDID Other Monitor Descriptors:
 140     // If the descriptor contains the display name, it has the following
 141     // structure:
 142     //   bytes 0-2, 4: \0
 143     //   byte 3: descriptor type, defined above.
 144     //   bytes 5-17: text data, ending with \r, padding with spaces
 145     // we should check bytes 0-2 and 4, since it may have other values in
 146     // case that the descriptor contains other type of data.
 147     if (edid[offset] == 0 && edid[offset + 1] == 0 && edid[offset + 2] == 0 &&
 148         edid[offset + 3] == kMonitorNameDescriptor && edid[offset + 4] == 0 &&
 149         human_readable_name) {
 150       std::string found_name(reinterpret_cast<const char*>(&edid[offset + 5]),
 151                              kDescriptorLength - 5);
 152       base::TrimWhitespaceASCII(
 153           found_name, base::TRIM_TRAILING, human_readable_name);
 154       continue;
 155     }
 156   }
 157
 158   // Verify if the |human_readable_name| consists of printable characters only.
 159   // TODO(oshima|muka): Consider replacing unprintable chars with white space.
 160   if (human_readable_name) {
 161     for (size_t i = 0; i < human_readable_name->size(); ++i) {
 162       char c = (*human_readable_name)[i];
 163       if (!isascii(c) || !isprint(c)) {
 164         human_readable_name->clear();
 165         LOG(ERROR) << "invalid EDID: human unreadable char in name";
 166         return false;
 167       }
 168     }
 169   }
 170
 171   return true;
 172 }
 173
 174 bool ParseOutputOverscanFlag(const std::vector<uint8_t>& edid,
 175                              bool* flag) {
 176   // See http://en.wikipedia.org/wiki/Extended_display_identification_data
 177   // for the extension format of EDID.  Also see EIA/CEA-861 spec for
 178   // the format of the extensions and how video capability is encoded.
 179   //  - byte 0: tag.  should be 02h.
 180   //  - byte 1: revision.  only cares revision 3 (03h).
 181   //  - byte 4-: data block.
 182   const unsigned int kExtensionBase = 128;
 183   const unsigned int kExtensionSize = 128;
 184   const unsigned int kNumExtensionsOffset = 126;
 185   const unsigned int kDataBlockOffset = 4;
 186   const unsigned char kCEAExtensionTag = '\x02';
 187   const unsigned char kExpectedExtensionRevision = '\x03';
 188   const unsigned char kExtendedTag = 7;
 189   const unsigned char kExtendedVideoCapabilityTag = 0;
 190   const unsigned int kPTOverscan = 4;
 191   const unsigned int kITOverscan = 2;
 192   const unsigned int kCEOverscan = 0;
 193
 194   if (edid.size() <= kNumExtensionsOffset)
 195     return false;
 196
 197   unsigned char num_extensions = edid[kNumExtensionsOffset];
 198
 199   for (size_t i = 0; i < num_extensions; ++i) {
 200     // Skip parsing the whole extension if size is not enough.
 201     if (edid.size() < kExtensionBase + (i + 1) * kExtensionSize)
 202       break;
 203
 204     size_t extension_offset = kExtensionBase + i * kExtensionSize;
 205     unsigned char tag = edid[extension_offset];
 206     unsigned char revision = edid[extension_offset + 1];
 207     if (tag != kCEAExtensionTag || revision != kExpectedExtensionRevision)
 208       continue;
 209
 210     unsigned char timing_descriptors_start = std::min(
 211         edid[extension_offset + 2], static_cast<unsigned char>(kExtensionSize));
 212
 213     for (size_t data_offset = extension_offset + kDataBlockOffset;
 214          data_offset < extension_offset + timing_descriptors_start;) {
 215       // A data block is encoded as:
 216       // - byte 1 high 3 bits: tag. '07' for extended tags.
 217       // - byte 1 remaining bits: the length of data block.
 218       // - byte 2: the extended tag.  '0' for video capability.
 219       // - byte 3: the capability.
 220       unsigned char tag = edid[data_offset] >> 5;
 221       unsigned char payload_length = edid[data_offset] & 0x1f;
 222       if (data_offset + payload_length > edid.size())
 223         break;
 224
 225       if (tag != kExtendedTag || payload_length < 2 ||
 226           edid[data_offset + 1] != kExtendedVideoCapabilityTag) {
 227         data_offset += payload_length + 1;
 228         continue;
 229       }
 230
 231       // The difference between preferred, IT, and CE video formats
 232       // doesn't matter. Sets |flag| to true if any of these flags are true.
 233       if ((edid[data_offset + 2] & (1 << kPTOverscan)) ||
 234           (edid[data_offset + 2] & (1 << kITOverscan)) ||
 235           (edid[data_offset + 2] & (1 << kCEOverscan))) {
 236         *flag = true;
 237       } else {
 238         *flag = false;
 239       }
 240       return true;
 241     }
 242   }
 243
 244   return false;
 245 }
 246
 247 }  // namespace ui