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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "ui/display/util/edid_parser.h"
#include <algorithm>
#include "base/hash.h"
#include "base/strings/string_util.h"
#include "base/sys_byteorder.h"
namespace ui {
namespace {
// Returns 64-bit persistent ID for the specified manufacturer's ID and
// product_code_hash, and the index of the output it is connected to.
// |output_index| is used to distinguish the displays of the same type. For
// example, swapping two identical display between two outputs will not be
// treated as swap. The 'serial number' field in EDID isn't used here because
// it is not guaranteed to have unique number and it may have the same fixed
// value (like 0).
int64_t GetID(uint16_t manufacturer_id,
uint32_t product_code_hash,
uint8_t output_index) {
return ((static_cast<int64_t>(manufacturer_id) << 40) |
(static_cast<int64_t>(product_code_hash) << 8) | output_index);
}
} // namespace
bool GetDisplayIdFromEDID(const std::vector<uint8_t>& edid,
uint8_t output_index,
int64_t* display_id_out) {
uint16_t manufacturer_id = 0;
std::string product_name;
// ParseOutputDeviceData fails if it doesn't have product_name.
ParseOutputDeviceData(edid, &manufacturer_id, &product_name);
// Generates product specific value from product_name instead of product code.
// See crbug.com/240341
uint32_t product_code_hash = product_name.empty() ?
0 : base::Hash(product_name);
if (manufacturer_id != 0) {
// An ID based on display's index will be assigned later if this call
// fails.
*display_id_out = GetID(
manufacturer_id, product_code_hash, output_index);
return true;
}
return false;
}
bool ParseOutputDeviceData(const std::vector<uint8_t>& edid,
uint16_t* manufacturer_id,
std::string* human_readable_name) {
// See http://en.wikipedia.org/wiki/Extended_display_identification_data
// for the details of EDID data format. We use the following data:
// bytes 8-9: manufacturer EISA ID, in big-endian
// bytes 54-125: four descriptors (18-bytes each) which may contain
// the display name.
const unsigned int kManufacturerOffset = 8;
const unsigned int kManufacturerLength = 2;
const unsigned int kDescriptorOffset = 54;
const unsigned int kNumDescriptors = 4;
const unsigned int kDescriptorLength = 18;
// The specifier types.
const unsigned char kMonitorNameDescriptor = 0xfc;
if (manufacturer_id) {
if (edid.size() < kManufacturerOffset + kManufacturerLength) {
LOG(ERROR) << "too short EDID data: manifacturer id";
return false;
}
*manufacturer_id =
*reinterpret_cast<const uint16_t*>(&edid[kManufacturerOffset]);
#if defined(ARCH_CPU_LITTLE_ENDIAN)
*manufacturer_id = base::ByteSwap(*manufacturer_id);
#endif
}
if (!human_readable_name)
return true;
human_readable_name->clear();
for (unsigned int i = 0; i < kNumDescriptors; ++i) {
if (edid.size() < kDescriptorOffset + (i + 1) * kDescriptorLength)
break;
size_t offset = kDescriptorOffset + i * kDescriptorLength;
// If the descriptor contains the display name, it has the following
// structure:
// bytes 0-2, 4: \0
// byte 3: descriptor type, defined above.
// bytes 5-17: text data, ending with \r, padding with spaces
// we should check bytes 0-2 and 4, since it may have other values in
// case that the descriptor contains other type of data.
if (edid[offset] == 0 && edid[offset + 1] == 0 && edid[offset + 2] == 0 &&
edid[offset + 3] == kMonitorNameDescriptor && edid[offset + 4] == 0) {
std::string found_name(reinterpret_cast<const char*>(&edid[offset + 5]),
kDescriptorLength - 5);
base::TrimWhitespaceASCII(
found_name, base::TRIM_TRAILING, human_readable_name);
break;
}
}
// Verify if the |human_readable_name| consists of printable characters only.
for (size_t i = 0; i < human_readable_name->size(); ++i) {
char c = (*human_readable_name)[i];
if (!isascii(c) || !isprint(c)) {
human_readable_name->clear();
LOG(ERROR) << "invalid EDID: human unreadable char in name";
return false;
}
}
return true;
}
bool ParseOutputOverscanFlag(const std::vector<uint8_t>& edid,
bool* flag) {
// See http://en.wikipedia.org/wiki/Extended_display_identification_data
// for the extension format of EDID. Also see EIA/CEA-861 spec for
// the format of the extensions and how video capability is encoded.
// - byte 0: tag. should be 02h.
// - byte 1: revision. only cares revision 3 (03h).
// - byte 4-: data block.
const unsigned int kExtensionBase = 128;
const unsigned int kExtensionSize = 128;
const unsigned int kNumExtensionsOffset = 126;
const unsigned int kDataBlockOffset = 4;
const unsigned char kCEAExtensionTag = '\x02';
const unsigned char kExpectedExtensionRevision = '\x03';
const unsigned char kExtendedTag = 7;
const unsigned char kExtendedVideoCapabilityTag = 0;
const unsigned int kPTOverscan = 4;
const unsigned int kITOverscan = 2;
const unsigned int kCEOverscan = 0;
if (edid.size() <= kNumExtensionsOffset)
return false;
unsigned char num_extensions = edid[kNumExtensionsOffset];
for (size_t i = 0; i < num_extensions; ++i) {
// Skip parsing the whole extension if size is not enough.
if (edid.size() < kExtensionBase + (i + 1) * kExtensionSize)
break;
size_t extension_offset = kExtensionBase + i * kExtensionSize;
unsigned char tag = edid[extension_offset];
unsigned char revision = edid[extension_offset + 1];
if (tag != kCEAExtensionTag || revision != kExpectedExtensionRevision)
continue;
unsigned char timing_descriptors_start = std::min(
edid[extension_offset + 2], static_cast<unsigned char>(kExtensionSize));
for (size_t data_offset = extension_offset + kDataBlockOffset;
data_offset < extension_offset + timing_descriptors_start;) {
// A data block is encoded as:
// - byte 1 high 3 bits: tag. '07' for extended tags.
// - byte 1 remaining bits: the length of data block.
// - byte 2: the extended tag. '0' for video capability.
// - byte 3: the capability.
unsigned char tag = edid[data_offset] >> 5;
unsigned char payload_length = edid[data_offset] & 0x1f;
if (data_offset + payload_length > edid.size())
break;
if (tag != kExtendedTag || payload_length < 2 ||
edid[data_offset + 1] != kExtendedVideoCapabilityTag) {
data_offset += payload_length + 1;
continue;
}
// The difference between preferred, IT, and CE video formats
// doesn't matter. Sets |flag| to true if any of these flags are true.
if ((edid[data_offset + 2] & (1 << kPTOverscan)) ||
(edid[data_offset + 2] & (1 << kITOverscan)) ||
(edid[data_offset + 2] & (1 << kCEOverscan))) {
*flag = true;
} else {
*flag = false;
}
return true;
}
}
return false;
}
} // namespace ui
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