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 13 namespace ui { 14 15 namespace { 16 17 // Returns 64-bit persistent ID for the specified manufacturer's ID and 18 // product_code_hash, and the index of the output it is connected to. 19 // |output_index| is used to distinguish the displays of the same type. For 20 // example, swapping two identical display between two outputs will not be 21 // treated as swap. The 'serial number' field in EDID isn't used here because 22 // it is not guaranteed to have unique number and it may have the same fixed 23 // value (like 0). 24 int64_t GetID(uint16_t manufacturer_id, 25 uint32_t product_code_hash, 26 uint8_t output_index) { 27 return ((static_cast<int64_t>(manufacturer_id) << 40) | 28 (static_cast<int64_t>(product_code_hash) << 8) | output_index); 29 } 30 31 } // namespace 32 33 bool GetDisplayIdFromEDID(const std::vector<uint8_t>& edid, 34 uint8_t output_index, 35 int64_t* display_id_out) { 36 uint16_t manufacturer_id = 0; 37 std::string product_name; 38 39 // ParseOutputDeviceData fails if it doesn't have product_name. 40 ParseOutputDeviceData(edid, &manufacturer_id, &product_name); 41 42 // Generates product specific value from product_name instead of product code. 43 // See crbug.com/240341 44 uint32_t product_code_hash = product_name.empty() ? 45 0 : base::Hash(product_name); 46 if (manufacturer_id != 0) { 47 // An ID based on display's index will be assigned later if this call 48 // fails. 49 *display_id_out = GetID( 50 manufacturer_id, product_code_hash, output_index); 51 return true; 52 } 53 return false; 54 } 55 56 bool ParseOutputDeviceData(const std::vector<uint8_t>& edid, 57 uint16_t* manufacturer_id, 58 std::string* human_readable_name) { 59 // See http://en.wikipedia.org/wiki/Extended_display_identification_data 60 // for the details of EDID data format. We use the following data: 61 // bytes 8-9: manufacturer EISA ID, in big-endian 62 // bytes 54-125: four descriptors (18-bytes each) which may contain 63 // the display name. 64 const unsigned int kManufacturerOffset = 8; 65 const unsigned int kManufacturerLength = 2; 66 const unsigned int kDescriptorOffset = 54; 67 const unsigned int kNumDescriptors = 4; 68 const unsigned int kDescriptorLength = 18; 69 // The specifier types. 70 const unsigned char kMonitorNameDescriptor = 0xfc; 71 72 if (manufacturer_id) { 73 if (edid.size() < kManufacturerOffset + kManufacturerLength) { 74 LOG(ERROR) << "too short EDID data: manifacturer id"; 75 return false; 76 } 77 78 *manufacturer_id = 79 *reinterpret_cast<const uint16_t*>(&edid[kManufacturerOffset]); 80 #if defined(ARCH_CPU_LITTLE_ENDIAN) 81 *manufacturer_id = base::ByteSwap(*manufacturer_id); 82 #endif 83 } 84 85 if (!human_readable_name) 86 return true; 87 88 human_readable_name->clear(); 89 for (unsigned int i = 0; i < kNumDescriptors; ++i) { 90 if (edid.size() < kDescriptorOffset + (i + 1) * kDescriptorLength) 91 break; 92 93 size_t offset = kDescriptorOffset + i * kDescriptorLength; 94 // If the descriptor contains the display name, it has the following 95 // structure: 96 // bytes 0-2, 4: \0 97 // byte 3: descriptor type, defined above. 98 // bytes 5-17: text data, ending with \r, padding with spaces 99 // we should check bytes 0-2 and 4, since it may have other values in 100 // case that the descriptor contains other type of data. 101 if (edid[offset] == 0 && edid[offset + 1] == 0 && edid[offset + 2] == 0 && 102 edid[offset + 3] == kMonitorNameDescriptor && edid[offset + 4] == 0) { 103 std::string found_name(reinterpret_cast<const char*>(&edid[offset + 5]), 104 kDescriptorLength - 5); 105 base::TrimWhitespaceASCII( 106 found_name, base::TRIM_TRAILING, human_readable_name); 107 break; 108 } 109 } 110 111 // Verify if the |human_readable_name| consists of printable characters only. 112 for (size_t i = 0; i < human_readable_name->size(); ++i) { 113 char c = (*human_readable_name)[i]; 114 if (!isascii(c) || !isprint(c)) { 115 human_readable_name->clear(); 116 LOG(ERROR) << "invalid EDID: human unreadable char in name"; 117 return false; 118 } 119 } 120 121 return true; 122 } 123 124 bool ParseOutputOverscanFlag(const std::vector<uint8_t>& edid, 125 bool* flag) { 126 // See http://en.wikipedia.org/wiki/Extended_display_identification_data 127 // for the extension format of EDID. Also see EIA/CEA-861 spec for 128 // the format of the extensions and how video capability is encoded. 129 // - byte 0: tag. should be 02h. 130 // - byte 1: revision. only cares revision 3 (03h). 131 // - byte 4-: data block. 132 const unsigned int kExtensionBase = 128; 133 const unsigned int kExtensionSize = 128; 134 const unsigned int kNumExtensionsOffset = 126; 135 const unsigned int kDataBlockOffset = 4; 136 const unsigned char kCEAExtensionTag = '\x02'; 137 const unsigned char kExpectedExtensionRevision = '\x03'; 138 const unsigned char kExtendedTag = 7; 139 const unsigned char kExtendedVideoCapabilityTag = 0; 140 const unsigned int kPTOverscan = 4; 141 const unsigned int kITOverscan = 2; 142 const unsigned int kCEOverscan = 0; 143 144 if (edid.size() <= kNumExtensionsOffset) 145 return false; 146 147 unsigned char num_extensions = edid[kNumExtensionsOffset]; 148 149 for (size_t i = 0; i < num_extensions; ++i) { 150 // Skip parsing the whole extension if size is not enough. 151 if (edid.size() < kExtensionBase + (i + 1) * kExtensionSize) 152 break; 153 154 size_t extension_offset = kExtensionBase + i * kExtensionSize; 155 unsigned char tag = edid[extension_offset]; 156 unsigned char revision = edid[extension_offset + 1]; 157 if (tag != kCEAExtensionTag || revision != kExpectedExtensionRevision) 158 continue; 159 160 unsigned char timing_descriptors_start = std::min( 161 edid[extension_offset + 2], static_cast<unsigned char>(kExtensionSize)); 162 163 for (size_t data_offset = extension_offset + kDataBlockOffset; 164 data_offset < extension_offset + timing_descriptors_start;) { 165 // A data block is encoded as: 166 // - byte 1 high 3 bits: tag. '07' for extended tags. 167 // - byte 1 remaining bits: the length of data block. 168 // - byte 2: the extended tag. '0' for video capability. 169 // - byte 3: the capability. 170 unsigned char tag = edid[data_offset] >> 5; 171 unsigned char payload_length = edid[data_offset] & 0x1f; 172 if (data_offset + payload_length > edid.size()) 173 break; 174 175 if (tag != kExtendedTag || payload_length < 2 || 176 edid[data_offset + 1] != kExtendedVideoCapabilityTag) { 177 data_offset += payload_length + 1; 178 continue; 179 } 180 181 // The difference between preferred, IT, and CE video formats 182 // doesn't matter. Sets |flag| to true if any of these flags are true. 183 if ((edid[data_offset + 2] & (1 << kPTOverscan)) || 184 (edid[data_offset + 2] & (1 << kITOverscan)) || 185 (edid[data_offset + 2] & (1 << kCEOverscan))) { 186 *flag = true; 187 } else { 188 *flag = false; 189 } 190 return true; 191 } 192 } 193 194 return false; 195 } 196 197 } // namespace ui 198
