[sensors] Ambient light sensor implementation for ChromeOS and Linux.

device/generic_sensor/ambient_light_reader_iio.cc

+// Copyright 2015 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 "device/generic_sensor/ambient_light_reader_iio.h"
+
+#include "base/files/file_enumerator.h"
+#include "base/files/file_util.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
+
+namespace device {
+
+namespace {
+
+// Base path where sensors are located.
+const base::FilePath::CharType kAmbientLightIioBasePath[] =
+    FILE_PATH_LITERAL("/sys/bus/iio/devices");
+
+}  // namespace
+
+AmbientLightSensorReaderIio::AmbientLightSensorReaderIio() = default;
+AmbientLightSensorReaderIio::~AmbientLightSensorReaderIio() = default;
+
+bool AmbientLightSensorReaderIio::ReadSensorLuxValue(double* lux) {
+  *lux = std::numeric_limits<double>::infinity();
+  std::string value;
+  if (!base::ReadFileToString(sensor_path_, &value))
+    return false;
+
+  base::TrimWhitespaceASCII(value, base::TRIM_ALL, &value);
+  if (!base::StringToDouble(value, lux))
+    return false;
+  return true;
+}
+
+bool AmbientLightSensorReaderIio::DetectLightSensor() {
+  // Search the iio/devices directory for a subdirectory (eg "device0" or
+  // "iio:device0") that contains the "[in_]illuminance[0]_{input|raw}" file.
+  base::FileEnumerator dir_enumerator(base::FilePath(kAmbientLightIioBasePath),
+                                      false, base::FileEnumerator::DIRECTORIES);
+  const char* input_names[] = {
+      "in_illuminance0_input", "in_illuminance_input", "in_illuminance0_raw",
+      "in_illuminance_raw",    "illuminance0_input",
+  };
+
+  for (base::FilePath check_path = dir_enumerator.Next(); !check_path.empty();
+       check_path = dir_enumerator.Next()) {
+    for (unsigned int i = 0; i < arraysize(input_names); i++) {
+      base::FilePath als_path = check_path.Append(input_names[i]);
+      if (base::PathExists(als_path)) {
+        sensor_path_ = als_path;
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+}  // namespace content